-->

FOREWORD

"I thank Dr. Derek Sikes for his help in obtaining this translation of Pukowski's classic 1933 paper on Nicrophorus.

The text is thorough and very detailed and a link to a succinct summary
is to be found in the Table of Contents labelled 'SUMMARY'.

Note that the paper refers to the original genus name of Necrophorus.
Whereas current useage now refers to the genus as Nicrophorus."

A Dale,
http://www.bugsandweeds.co.uk


 

ENGLISH TRANSLATION OF PUKOWSKI'S 1933 NICROPHORUS PAPER

The following was translated from the German by Janet Christie and originally posted by Derek Sikes. Refer to the original document for literature cited, tables and figures, which are not included here. This reproduction is not to be used for any purpose other than private study, scholarship, or research.


Ecological Investigation of Necrophorus F.

-

by

Erna Pukowski

Zeitschrift fur Morphologie und Oekologie

der Tiere 27(3): 518-586. 1933.

 

 

TABLE OF CONTENTS

INTRODUCTION


RESULTS

A. General Life of the Adult

1. Occurrence -- frequency
2. Environment
3. Temporal occurence
4. Nutrition

B. Reproductive Biology

1. Relationship of beetles to one another

a. Attraction of females
b. The isolation of pairs from a large number of
individuals end the resulting conclusion
c. Ecology of the fight
d. Fight with strange species or races of
gravedigger
e. Course of the fight
f. Relations between partners of the pairs


2. Relations of the beetles to their offspring

a. Brood care
b. Burying of a body
c. Rounding of the body and completion of the
crypt
d. Egglaying
e. Moisture and digestion of the body
f. Male participation in brood care
g. The brood at the time of larval development
h. Feeding of the larvae
i. Ecology of feeding
j. Defense of the larvae and their food
k. Maintenance of the crypt
l. Defense of males at the nursing
m. Development of full-grown larvae to young beetles

SUMMARY



INTRODUCTION

The striking instinct of gravediggers (Necrophorus fabricuis) to bury small animals was first reported by Gleditsch (1752) with the help of experiments, in which development of beetles with different species of small animal corpses at their disposal was observed. Gleditsch succeeded in putting the burywork of the gravediggers in relation to their reproduction. On the suggestion of these chemists Melim from Bremer (1755) who independent of the mentioned report, followed the burial of a mole by the gravedigger and recognized in them the remarkable broodcare, which also occupied A. I. Rosel von Rosenhof (1761) with the remarkable life of the gravedigger. We find his result put down in the celebrated "In sektenbelustigung" equipped with coloured pictures of adults, larvae and pupae.

From the statement of Gleditsch (1752) that a gravedigger had brought a stick to undermining to collapse was fed on the body of a toad, Lacordaire concluded about the intelligence of this beetle. First the French researcher J. H. Fabre destroyed the fable of the intelligence of the gravedigger while he showed with the help of numerous carefully carried-out experiments that the actions of this animal are fixed within the setting of instinct, but not as was first interpreted a reasoned thought.

If the experiments of Fabre lead to greater clarity so too a new problem escaped his observations that researchers had perceived as such, but not been able to solve. This new problem lies in the fact that on the buried carrion there always remains a single pair of gravediggers, highly suitably, even if more beetles worked at it. The question of how this appearance is to be explained was discussed recently in terms of animal psychology and sociology (Renter 1913, Schroder 1929) however until now no satisfactory solution was found. On the suggestion of my highly revered lecturer, Herr Geheimen Regierungsratses (private administrator adviser) Prof. Dr. zur Strarsen, I put the solution of named problem to the test.

Fulfillment of the task required most precise knowledge of the whole digging event within which the isolation of pairs from a larger number of individuals must take place; this could only be achieved through extensive experiments preferably under natural conditions. For this reason I have investigated in depth the general ecology of the genus Necrophorus.

The experiments were carried out on the following species: Necrophorus germanicus L., humator B1., vesplllo L., vespilloides Herbst, investigator Zett, fossor Er. (interruptus Steph.) The species germanicus, was sent to me mostly from Danzig; I baited the other animals around Frankfurt a.M.

RESULTS


A. General Life of the Adult

1. Occurrence - frequency.

Although around Frankfurt not all species of the genus Necrophorus occur, humator, vespillo, vespilloides, fossor and investigator still occur with certainty. The first three species are found in large quantity, and investigator and fossor in smaller quantity. N. germanicus is scarce and N. vestigator even more so.


In order to catch the gravediggers, I arranged measures of bait in the following state: a pail, whose base was perforated for the draining of rainwater filled to 10-15 cm with earth. Inside a slightly decaying large piece of meat was laid and the entire pail was put so that it is not exposed to direct sunbeams, yet still breezy enough for the smell of the carrion to flow about unhindered. Beetles flying by are easily able to attain the body; but there they are caught for the narrow limit of space left them is too little for flying away and they are not able to clamber up the smooth and steep walls of the pail. Besides few make attempts to fly for there they find rich booty and the soil layer offers them the possibility of shelter. Every 10-14 days the traps were baited with inew meat, and were able to be used continuously in this way.

In order to give a rough impression of the frequency of the gravediggers, I have included 3 tables which give again the total yields of the baits. The catch was made after the meat had layed out for 3-4 days in warm weather. On baits M.S., M.E. and M.W. named beetle species in the following numbers were found. From this set up it is obvious that the gravediggers are by no means as rare as one accepted from chance finding.

2. Environment

The searching of numerous baits gave me the opportunity to study the occurrence of frequent species (humator, vespillo, vespilloides) around Frankfurt a.M. with regard to their environment and to confirm the winning conception with a systematically employed series of experiments. The traps were put out in different areas of the nearer and farther surroundings of Frankfurt, and the caught animals registered with time, numbers and species. Data in Table 1 are from a large series of arbitrary catches. The baits are labelled with the numbers I-VI. All catches given here were made at the same time of year, namely mid Mav 1931. M (bait) I and M II were in Tannus near Eppstein. Distant mixed woodland (Pinus and Fagus) is the near and far environment. M III and M IV were in meadows at Ginnheim and Rodelheim in Niddatal which stretches to the foot of Tannus. M V stood in the middle of a large, very dry confer wood area in Frankfurter Stadtwald. M VI lay in mixed woodland (Pinus, Picea, Fagus) in Walldorf and close to the woodedge not far from extensive meadowland. So M VI joined the environmental conditions of previously chosen places.

From Table I in mixed woodland from Eppstein at M I and II altogether 41 individuals of humator and 36 of vespilloides were found, but not a single example of vespillo. Forty-four examples of N. vespillo were found from meadows at Ginnheim and Rodelheim in M III and M IV. However M III and M IV show uniform vespillo- material. The yield in pine stock brings a new species picture. Here in M V the domination of N. vespilloides really comes to light. Only at M VI are the three N. species commonly found.

This proves that the findings of the single catching points at the same time of year concerning the species distribution are by no means all equal to each other. Rather it looks as though clearly there is a factor governing the occurrence in appearance: The habitat of N. vespillo is meadowland, while humator and vespilloides are indigenous to woodland. M VI supports as its surroundings are mixed woodland as well as meadow, the importance of control experiments. Correspondingly examples are found of humator and vespilloides which come from the adjoining meadow. Those in the mid-part of the table containing beetle numbers perhaps appear scarce. But the unquoted records of the same year (1931) as well as the records for 1929, 1930, and 1932, extend the total to 2357 examples, and corroborate the reported results, eliminating the probability that these patterns are due to chance alone.

Naturally, the membership of a species to a clearly defined environment from the records must be all the clearer, all any time a habitat and untroubled from strange intruders opposed to them. For the species vespillo it was possible to employ a trial experiment in a handy absolute territory. It was carried out in Freistaat Danzig at a place where there is no woodland for many kilometres in circumference. The experiment caught 64 examples of N. vespillo and one of N. vestigator. Trapping in Freistaat Danzig, on different ground confirmed the Frankfurt results. It was possible in Frankfurt in spite of little expansion of affiliated areas, to construct a correlation of species and environment showing a considerable environmental loyalty of the species. This applies particularly to N. humator and N. vespilloides, which in general were found not more than about 100 m distance from woodedge; while vespillo advanced a kilometer into the woods.

The results from M V in Table I indicate that N. vespilloides is found predominantly in stands of confer wood. Hence its occurrence in mixed wood was due to the presence of scattered pine stands while N. humator occurred particularly in deciduous woods. Although this hypothesis is supported by numerous results, isolated results still occur which directly contradict this. A moment on the ecology of Nicrophorus however helps to eliminate the apparent contradiction. Because the gravedigger buries small carrion as food for the descendants, they are dependent upon the condition of the ground which offers unequal resistance depending upon the material covering the ground. The conifer woods, which appear as pine woods in a large part of the Frankfurt area, stand here on predominantly very dry, sandy ground. The ground is almost free from rooted plants, covered with an even rough humus layer of needle litter which is interrupted here and there by small moss lawns (Hypnum, Polystichum species). Elsewhere the ground is damp,deciduous leaf woods, which in west Germany is mostly dark brown to black crumbling humus with a far higher moisture content than the sandy ground of pinewoods. Its covering with leaf-litter and loosely twisted roots of ground plants, is about average in resistance to mechanical destruction falling between the loose leaf litter of pinewood and the dense layer of roots of meadows. The ground of valley meadows (and only these are common here) is heavy and moist to wet. It bears an extremely dense root layer of its predominantly Gramineae covering.

The described soils differ so strongly from one another in their condition that it was understandable, when every N. species preferred for digging capability and behavior an adequate environment. There is also clay-sandy deciduous wood soil and moist to marshy pine wood soil. At such;places. the picture appears reversed exceptionally. In wet pinewood N.humator rules but in dry deciduous wood N. vespilloldes does thus accounting for the above contradiction. The exception offers the best proof that the ground is the primary habitat characteristic for the-gravedigger.


Extreme differences from the rules are rare in the Frankfurt area. More frequently one finds that the relative population between N.vespilloides and N.humator in mixed woodland shifts in favor of one or other sides only somewhat. according to whether the experiment was put in a dry, sandy or a more damp, humus mixed wood. For example the yield from M I and M II in mixed woodland of the Tannus in Table I shows the proportion 41:36 where N. humator forms the larger quantity. In mixed wood of sandy urban woods likewise both species are found, but in totally changed proportion (Results M.S. S.520), 7 N. humator and 69 N. vespilloides. The sample numbers of N. vespillo from adjacent meadowland were approached in the woods.

3. Temporal occurrence

The baits were visited during the warmer times of the year for Necrophorus species. The more or less early time appearance of beetles in the spring as with their disappearance in autumn is naturally dependent on favorable or unfavorable weather. In 1930, the spring was warm, and on 4 April the first gravedigger, N. humator, although the bait was on the edge of a small, damp deciduous wood in the middle of a further stretch of meadow equally favorable to N. vespillo. N. vespillo appeared for the first time that year 16 days later. Due to cold springs in 1931 and 1932 I cannot say what the average date of appearance is. In both cases the animals did not appear until May and they were caught at the same time. While N. humator, N. vespillo and N. vespilloides appear at approximately the same time and also disappear to hibernate at the same time. N. investigator and N. fossor (interruptus) make a striking exception. These species were not found until the end of June or beginning of July during all three summers of the study (1930, 1931, 1932). The late appearance of these species is connected with their individual cycles which are delayed for months in relation to the 3 other species, N. humator, N. vespillo, N. vespilloides. On particularly warm November days one finds here and there flying Necrophorus but as a rule, all species begin their hibernation around the beginning to middle of Octoher.

Although gravediggers were recorded as common animals, one rarely finds them without the aid of bait. This is based on their nocturnal life style. The gravedigger comes out of the ground in which he has been secreted for the day, around sunset. If one observes this happening, one sees as with a small shake of the ground two appearing antennae. Apparently the beetle examines the environment through his smelling organs. After that the animal leaves the sheltered province and climbs any blade of grass. In spite of his size and weight he brings this about with dexterity. If the grass bends to the ground under his weight, another blade is climbed. Apparently, the beetle operates by instinct, to raise himself somewhat above ground level. In this way he manages to contact initially the light scents from possible food and secondly he can lighten himself for take-off. There he remains sitting preening himself with antennae moving, ready to begin his flight in search of food.

The gravediggers are pronounced dusk and night animals when living in a well maintained terrarium of 50-60 beetles and only rarely does one appear in the daytime. If the environmental conditions are unfavorable for the beetles, e.g. strong sunlight, high temperature, extreme drought, narrowness of cage and lack of food, they are driven to the surface during the daytime. They then undertake rapid running around and continual attempts to escape in which they fly round wildly. These are however clear reactions to abnormal conditions.

In certain cases the Necrophorus can indeed be found also during the day in natural conditions. Every animal which has found carrion at night stays there during the day. There they hide on the underside or slide inside in some which contain cavities within, where they are able to devote themselves to undisturbed feeding. Often on windy but sunny spring or late autumn days, thus shortly before or after the winter hibernation of the animals, one sees flying Necrophorus. Probably they are driven to it by the hunger, and that at all times of the night it is too cold to search for food.

Their life in the dark of night or the soil makes the gravedigger correspondingly sensitive to bright light, yet the degree of sensitivity varies with the individual. Most times they retire into the soil with sudden lighting with white light individual answers to a strong light attraction done with Thanabos. Others again are not disturbed in their occupation. In strongly softened light one can observe almost all individuals undisturbed. For this reason this sort of illumination was employed chiefly for observation.

4. Nutrition

In quick flights, thereby frequent and uninterrupted in varying direction, the gravediggers wander through woods and meadow till the wind carries to them the scent of carrion. At once the flight stops, flying round the source of the smell in narrow circles and finally land on it or in their near surroundings. In the last case one sees the beetle hurrying to his find with swinging antennae.

Although the Necrophorus lets himself be enticed to the scent of carrion, they are not exclusively carrion eaters, but predominantly predators. Already more than lOO years ago an English researcher, Bell, observed how gravediggers seized and consumed the fly larvae from a carcass. The description of this event, which was first published in 1873, has remained unnoticed and still long afterwards Necrophorus is reported as a typical carrion eater. Later Ch. U. Clark (1895) and W. T. Davis 1915 often have called attention to the predatory life style. Most recently F. Steele (1927) showed this in a perfect series of experiments on the North American gravediggers describing the facts of eating charmingly and vividly.

My experiments showing the preference for diptera larvae by European species is of value. It was especially pointed out that also N. vespilloides is no exception to the pattern of nutritional habits. The fact that this species was sometimes found in rotten woodland fungi, gave occasion to the statement (Chenu and Desmarest 1851), that N. vespilloides did not feed from carrion but only from fungi. But that is not true. Although these gravediggers were enticed through the smell to decomposing fungi, they were still only hunting for the living diptera larvae in the fungus. I saw a hungry male of this species consume 17 maggots in 35 minutes after which the meal was interrupted.

The predatory nature of the genus Necrophorus is clearest expressed in the species N. germanicus. In the night, this large, extremely agile animal hunts for Geotrupes unless fly maggots are within reach. Klungelhoffer (1843) and Schmidt (1883) always observed a fierce struggle between N. germanicus and Geotrupes (mutator) stercorarius and both concluded from that the predatory life style of N. germanicus. This conjecture I was able to confirm. I went along the following train of thought: If those observed cases from the above metioned authors are not chance records, particulary N. germanicus, rather instinctive hunting for Geotrupes it must be expected that it reacts to the smell of horse dung the typical habitat of their prey--as N. vespilloides reacts to the smell of fung. In order to prove this, the following experiment was set up.: In a round terrarium (lOOx94x58 cm) in which several N. germanicus were held, I brought some horse dung. The Necrophorus, which until this moment were wandering round apparently aimlessly in the cage, stopped with antennae beating keenly or others immediately began their direction of marching and hurried to the dung heap. This is possibly explained by the water or bacterial content in the fresh dung attracting the Necrophorus to approach. That however contradicts the behavior of the beetle when they have approached the source of the smell. None of them bite into the heap with their mandibles, rather all run as if searching it over and turn around now and again a large piece of dung with head and thorax. One cannot keep the false impression as these animals search the dung for its occupants. Single individuals withdraw, the majority however remain at the site and bury themselves superficially in the dung. One particularly lively female hid for example under a lump of dung. Only the head with perceiving antennae, was still to be seen. At this point I would like to take the opportunity to mention an observation of V. Lengearcken, who found a N. germanicus under a ball of horse dung lying in the wild. Animal and dung ball were already sunk somewhat into the ground. Undoubtedly it had to do with the same event which I was able to observe in the terrarium. There also I saw here and there how the dung was sunk somewhat into the earth through the agitation beneath the beetle.

So the beetles remain to a certain extent in ambush, only alternating now and then hastily leaving his place. This behaviour of the beetle then follows without there being any Geotrupes in the cage or in the vicinity! After a fresh dung pat is searched through for the Geotrupes by N. germanicus, they wait for the moment which enticed hy the smell of dung, happens with all probablity in a short time.

Now I placed about 60 Geotrupes into the terrarium. All belonged to the species G. sylvaticus, which I was able to collect most easily in the surroundings of Frankfurt. Nearly all the dung beetles groped about for a long time at the nearest way of the dung heap. Scarcely had the first reached their goal when those still inanimate predators became lively, appearing in masses. Everywhere the large predatory gravediggers claimed their prey which to begin with chirped loudly, but desperately, to defend themselves. Also the previously mentioned female left its place under the dungball and hurried smartly towards the near prey by the shortest route. N. germanicus attacked its prey not from ambush as one would presume from its initial behavior but hurried openly to his prey and seized it with legs and mandibles. Every caution appeared totally useless as the observer did not receive the impression that Geotrupes sylvaticus was able to recognize his enemy as such. One sees on the contrary the dung beetles marching on the Necrophorus and even in direct proximity no impression was noticeable.

That what took place now between the attacker and his prey can by no means be described as a struggle. For both animals are too unequal in strength and quickness. N. germanicus seized the weaker, G. sylvaticus with both legs and thereby threw itself on the back or the side. This pose was taken willingly as the eating of large fly maggots, so that more than half of the gravediggers can be found after a feed with these larvae, the prey held in front of them between first and second pairs of legs. Small fly larvae are nevertheless held free in the mandibles.

Through the extremely tight hold of predators, Geotrupes sylvaticus becomes pressed against the ventral side of its opponent and can be eaten conveniently. One hears loudly between the weakening chirping of the dung beetles cracking of the chitin armor under the strong mandibles of the gravediggers. At some point the outer skeleton becomes broken. In the majority of observed cases the prey was slit open on the ventral side of the area between pro- and meso-thorax. In other cases the predator succeeded in destroying the strongly chitinized (thorax) neck plate. Once the body is open, the organs are pulled out and eaten. In the course of half an hour I saw one N. germanicus male seize and consume five Geotrupes in the described way. The others who were no less lucky in their hunting so that the remainder of the Geotrupes lay around everywhere in the terrarium. The N. germanicus seizes the dung beetles so quickly when hungry, but they are indifferent to them in the satiated state, hurrying by without any attempted attacks on the Geotrupes.

The experiment was performed several times with the same results: N. germanicus habitually hunts for Geotrupes! To be sure, fly maggots and Geotrupes were offered to them at the same time and as a rule the fly maggots were preferred.

In spite of their preference for living prey Necrophorus show only a slight inclination for cannabalism. Healthy individuals did not cannabalize others when very hungry and under confined living conditions. An exception to this may arise in fresh, recently colored young beetles which at times consume uncolored individuals--usually brothers and sisters. This is seen only in rearing under artificial conditions,indicating environmental conditions as causative factors. While in nature the beetle immediately goes out in search of food after leaving the pupal stage, in the terrarium he is held back by enormously limited room. From deficiency in other food the animal seizes conspecifics which are convenient prey for him. This was easy to prevent; shortly before the hatching of the beetles some meat was put in the cage. Still in nature, cannabalism can occasionally be observed, when sick or hadly injured individuals are attacked and consumed.

Besides the predatory nutritional ways all here-mentioned, Necrophorus species are also carrion eaters. As Steele (1927) already mentioned for the North American species, he showed the little decayed food of the strongly decomposed. Largely independent of the type of meat, the Necrophorus accept every kind of carrion that is offered to them. Meat or internal organs of vertebrates such as sheep, pigs, beef, horse or even tiger and turtle soup whose bodies were placed at my disposal by chance served the gravediggers for food just as the bodies of small vertebrates or even many invertebrates like earthworms, slugs, and larger insects. When one puts a hungry animal on a piece of meat, it tests the food here and there with antennae and mouth appendages. In a somewhat damp and soaking place one sees it stick to and drive in its mandibles. The choice of place to eat corresponds to completely the preference of the gravedigger, on small vertebrate bodies firstly the body opening, eyes or possibly wounds as this also Steele (1927) was able to establish for those species which he had examined. Yet without having a visible ingredient cut off, the jaw becomes open again, in order to immediately grip to new dense area behind the place again, a match that is repeated so long with between the mandibles rises a weak border of ordered meat. One sees the mouth appendages working this border again and again. After a long time, often after an hour, the beetle turns to another place, without that, that border would have completely disappeared.

If one now disturbs the animal in some way, it vomits immediately a part of the food taken up, in which from microscopic examination are traced no formed ingredients. Therefore the meat is not devoured in small pieces, particularly rather milled through and pressed out by continual work of the mouth appendages to then take up the food in liquid form. The tough and hard tissue stays behind, as it also happens in the-consumption of a diptera larva whose cuticle stays behind--when also in young larvae till crushed to an unrecognisable state. Besides the mechanical work to gain liquid food, it would be possible that the material becomes liquified through the effect of a deposited extraintestinal gut secretions. Although the vomiting of a digestive secretion was not able to be explained up till now, certain observations and considerations make the surmised events probable: A fresh piece of insect from which a Necrophorus had eaten showed for a long time at the eating place distinct alteration. Brown color and jelly-like blurred contrasted the place clearly with almost unaltered surroundings. Further speaks the admitted factor, that disturbed gravediggers vomit intestine contents, respectively intestinal secretions for the operation of a preoral digestion during meals; to us this appearance is faced only in beetles with extraintestinal digestion. Further evidence for this species the food in-take by the nearest relations of the gravediggers, the Silphinae, is wide, as Heymons and V. Lengercken pointed out (1926-1932).

B. Reproductive Biology

1. Relationship of beetles to one another.

a) Attraction of females

In May the species N. vespillo, N. vespilloides, N. humator, and N. germanicus, in August the species N. investigator, N. fossor are already in reproduction. At this time the beetles begin with that activity to which their name gravedigger points: they bury small carrion in the soil in order to receive it as food for their descendants. Their gonads have developed immensely to a mature state, and both sexes happen now on the search for carrion that corresponds to the demand of their broodcare instincts, and describes at the same time the meeting-place for males and females. When a body is found and a pair are together then the preconditions for reproduction are fulfilled.

If only a male arrives at the carrion, one can make the following highly remarkable observation: the males which initially set about the digging work, break it off after a short time in an effort to reach a high point in the immediate vicinity of digging. The male climbs,a blade of grass, a stone or even a small heap of soil, for want of a high lying point. In all observed cases this is commonly a very surprising pose which

the male assumes. The animal orients itself so that the head is as low as possible but the abdomen stands as high as possible in space. The head is thereby bowed so low that the mandibles often rest on base, grass stalk, stone or soil. The whole body, which normally shows in every Necrophorus in front of as well as behind a distinct slope from the ventral aspect, becomes extended in a slope from behind causing a steep angle. The body weight thereby rests on fore and middle tarsi, while the hindlegs are only lightly placed or even held freely suspended. The hind end of the body is so strongly extended that the abdomen appears longer and more slender and the last segment which normally lies hidden in the body appears. In this position the male persists, refraining from short breaks without clearly visible alteration for more than an hour. Only the tip of the abdomen betrays slight swinging or rotating movement; the last segment stretches away from the others occasionally revealing the intersegmental membrane. I would like to describe this strange operation as the "Ventilation" of gravediggers.

What ecological meaning comes from the "ventilation" of male gravediggers? I was able to observe it 13 times, the results of which are summarized below.

1) The "ventilation" was regularly performed in the immediate vicinity of a carcass.

2) Ventilating animals were without exception males with ripe, plump full testes.

3) Never was a female observed in the vicinity.

4) Only on warm summer evenings (June, July, August) after sunset was ventilation able to be observed.

These facts suggest "ventilation" of male gravediggers involves the females. Presumably flowing from either the tip of the abdomen or the intersegmental membranes are sex or species specific scent to signal passing females and to guide their approach. This assumption is supported in that at times one sees both sexes coming to the carrion's scent. When the carrion is buried superficially by the male, thereby checking the enticing smells, the sex scent of the males was able to lure a female; a peculiar profit results for the prey is protected from any other carrion eaters, and remains reserved in all probability for the species.

The declared explanation also found experimental confirmation in degrees: after a series of failed experiments I succeeded finally in two cases in bringing to puberty males isolated on a carcass to "ventilate." That this experiment frequently failed, I believe goes back to the artificial environmental conditions. Out of the obvious assumption that the above mentioned points 1-4 are taken from, the size of the cage (my successful exp. were carried out in a cage of the dimensions of lOOx94x58 cm) and above all good ventilation are important in success.

So the term "ventilation" in the gravedigger ought to be authorized. Still it ought to be pointed out that a Necrophorus is not designed for a such extreme placement of the abdomen in ventilation. Although the movement of the hind body is not equal to that of Hymenoptera--a still striking apparent convergence finds the ventilation of gravediggers remaining like the termites. From Tollin (1862) a male termite that has found no partner through swarming who scarcely had begun digging work, stretched the abdomen in the air and stuck to it for many hours each day.

b. The isolation of pairs from a large number of individuals and the resulting conclusion.

When a male and female of the same species meet on a suitable body for broodcare (or the body has been found by an already paired female (vgl. S 539) the carrion is buried and serves the larvae as food, till they are full grown and move further into the soil for the pupation. At this time the store is consumed until from insignificant amount remaining, has sufficed even for the brood's parents. But what happens if the same quantity of food has to suffice for the brood of several females? Without doubt the development of all larvae would be greatly endangered through shortage of food. This danger is likely -for it happens often enough, that through the smell of the carrion several females are attracted with mature~ ovaries. How is the threatened danger averted?

J. H. Fabre (1899), as I have already mentioned in the introduction, made the striking statement that he never found several females on buried carcasses. Always he mentions only one pair there, even if beforehand more than two individuals had been working at the digging at the same time. My first task was to examine this declaration of Fabre for its accuracy. Fabre, known as a sophisticated observer, remains to be considered for this observational experiment on Necrophorus which was carried out in an aviary, therefore under artificial conditions, with only a limited number of beetles, namely 14 individuals. The question which I had to answer ran accordingly: is only one single pair really found on buried carrion in all cases, including under natural conditions?

All my experiments were made correspondingly in natural conditions--thus they were not successful. Through laying out suitable pieces of meat to attract the grave diggers, they were allowed to bury the prey undisturbed and after a known time the number of beetles remaining on the carrion was checked by digging it up. Digging up is too crude a method. Through the warning of shaking the ground, many beetles hide further into the soil and cannot be found and cautious digging is very time- consuming.

In order to avoid this disadvantage, 200 flower-pots (12 cm high, 14 cm diem. at top) were distributed in woods and meadows in the surroundings of Frankfurt. They were sunk in the soil to the upper edge and filled with dug material till full, after the base of the vessel was covered with a fine mesh wire net, to prevent the escape of beetles from beneath (Abb. 3). A small piece of meat about the size of a mouse was laid on the soil in the flower pot. On a small adjacent piece of wood a number was marked under which the results were entered in the records. The experimental site was visited several days in succession and observations made on them continuously registered. After the meat was sunk into the ground, through the work of grave diggers. I waited 2-3 days, then dug the flower pots from the ground and over turned them on a firm base. Its contents lay exposed in this experimental procedure and could be searched through without trouble, which is also of importance for later mentioned observations. Escape of beetles was excluded through this arrangement.

Although not all 200 experimental sites were in operation simultaneously (for the meat was eaten frequently by other animals or carried off by the gravediggers), I was still able to examine in the course of Summer 1930, 254 cases in the described way. An experiment was only counted then, when the carrion was found already in a subterranean hole, which Fabre called the crypt, there in the presence of this crypt for sole proof for the termination of digging work is recognized. The examination gave the following results.

In 197 of the mentioned cases a pair was found on the carrion or in the near vicinity within the flower-pot; in 53 cases, I was able only to find a female. In 4 cases I found in the near vicinity of the crypt 2 females (which by further investigation proved to be sexually mature). My experiment then proved perfectly that really only 1 female remains behind on the buried carrion and it has in the great majority of cases the male with it. The number of exceptions is so small that they may be neglected. Also it ought to be emphasized that the results were not being influenced substantially perhaps by the lack of competitors: in most cases more distant individuals were found in a small distance outside the flower pot in the soil.

If the initially asked question is answered in the affirmative, we are faced secondly with the problem of how the separation of a single pair is brought about from a large number of available candidates. This looks as if it involves animal psychology. But the apparently puzzling occurrence is clarified through broader consideration. The grave diggers dispute their right to possession of the carrion by fighting one another, and it is predominantly individuals of the same sex which fight.

The description of a typical start to an experiment comments on the cause of events in detail. In a spacious terrarium, 4 pairs of the species N. vespillo were introduced. Every female was marked with a color mark on the pronotum. All males received at the same time in the same color (white, light blue, light green and yellow) a mark on the elytra so one was able to recognize again at a glance the sex of the animal and at the same time the individual. The pairs were first confined to this experiment after they, separated from the others, had proved their sexual maturity through desire to dig.

On the day when the animals were committed resting onto the soil, I layed a dead mole on the soil surface in the middle of the cage. At sunset the first female (bright blue) appeared and hurried to the mole, climbed and clambered around on it, in order to disappear. Here & there the shaking of the dead body showed that the female was digging. Meanwhile the light green and yellow females also turned up. While the first ran here and there the corner of the cage, the yellow male marched smelling to the carrion. Arriving there it soon slipped under the body. While for several minutes nothing happened, till both animals, the bright blue female and the yellow male by chance at the same time came forth from under the mole, each at a different place. Now the female scent appears to come from the new comer (male). The female pauses visibly and runs directly to the male with quick steps, hesitates, reaches with the antennae the abdominal tip, that aggravates him, as the male has quickly hurried over by the approach of the female. Scarcely has the female succeeded in testing the hind end of male with tasting tips of the antennae, than it turns away. Then the male begins to follow the female. With a few, hasty skips it stops, a little shake with the antenna and with the loud chirping of both animals, mating takes place. After that the pair turn toward their work again.

In the corner of the terrarium, the second female appears level with the soil. It bears a white color on the neck plate and is already well known to me because of its strength and savageness. This beetle also goes to the carrion immediately and meets there with the female. Both go immediately one after another and both appear to recognize the smell of the hind end of the body of the sex of opponents. The movement of the grave digger at their work particularly on warm summer evenings was described already, and quickly mentioned, yet the aggressive savageness surprises so, with those in the situation the two females rushed at one another. The fight begins.

But, scarcely begun, it is already finished. The bright blue female, which at first had taken possession of the mole, left the place of the fight in a rush to escape. It searched the walls of cage and clambered at them, and as this did not succeed, it buried itself in the furthest corner. It was to be seen no more for the rest of the evening. The strong female with the white mark now crept under the mole where meanwhile the male was pursuing his work. The victorious female thus thrust aside the loser, and took possession of the prey itself. Soon it emerged again a few cm distance from the body. Close examination showed that it had created a passage, which began under the mole and ran to the surface here. One is reminded of passages which lead from the inside of old fortresses to freedom. In this security the female remains sitting till hidden to head and forelegs in the soil, and throws itself from here out onto every grave digger which wants to approach the carrion. First it is the light blue female that comes that way. Although after itself, the female has information about the sex of the approaching animal, it creeps under the carrion, and turns up there shortly again in the mouth of its subterranean passage. The newly arrived male occupies himself meanwhile with the digging work and has soon disappeared in the soil. An approaching female (yellow) is treated less peacefully. Scarcely had it shown its identity through its scent as such, than it was attacked savagely, and was driven away after a strong fight. The bright green female did not come off any differently. From this the white maintained its place. During the watch the guarding animal stayed directly in the soil. I sat the yellow, already once expelled female, with forceps on the mole. Then it had plenty of time to work, and was mated with the bright blue male. By accident the white female came into its vicinity, the fight was repeated, then again the yellow animal left. Now it was no longer possible, to bring the defeated female onto the mole and for it to remain there. I tried it so often, but these animals were good at escaping from these places. The strong female even set back the yellow, and then also attacked it, when I held it tightly with the forceps. Both layed into one another so quickly, that I was able to lift both fighters together without them separating. During these maneuvers a newly arrived male (white) succeeded in getting under the body unnoticed by the white female.

We see how well a female fared in the field of other females! How do the males behave among one another? The two worked during the whole duration of the experiment on the same carcass without mutually disturbing each other; the mole is sunk further into the soil through their common vehicles. Finally even a third male arrived. Suddenly, a loud chirping becomes audible and in a wild chase 2 males appear under the carrion, the third (white) close behind them. This comes (as in the females) at last usually to a fight, from which the white male comes off victorious and turns back to this work, while the fugitives appear to keep away from the mole now. After a further hour in which nothing more in particular happens and the mole is rapidly fully covered with soil, the observations were discontinued. On the following morning by digging it up, I found on the carrion the white pair alone, whose isolation had taken place in the described way.

If the described events are valid as typical, then they also show certain peculiarities. For example, the sort and manner as the victorious female creates an ambush in the form of a subterranean passage, do not describe the rule, although this was also observed in other females now and again. Frequently the female briefly undertook trips radiating out from the carrion but always returning to the body. I would like to interpret this behavior of the female as a species watch (guard) service, during this the close vicinity of possessions at risk is searched for strange females and prevents an unnoticed intruder going by. Further the experiment demonstrates that the second female was superior to all remaining in strength and drive to attack. If this were not the case, then the carrion could be conquered still by the third or even fourth female and so several times change owners.

The experimental description has shown in which way the fight between grave diggers of the same sex brings about the peculiarity of a single pair from a large number of individuals. It is true that the described mechanism is not absolutely clear, but still works with greater certainty except with a very small number of exceptions (4 out of 254 cases) in which two females were found on one and themselves buried the carrion.

But how is it, that 53 times only females were found. So far it is not a matter of cases in which a female mated elsewhere had layed out the burrow; this is the result of one female changing instinct after completing the passage digging. The female that puts up with a digging male, however, attacks after completion of the crypt of the partner and drives him away. Most of the females enter the change in behavior shortly after egg laying, yet can before; after this time the male can be expelled from the brood chamber. Under these circumstances, different sexes of the same species of grave diggers alone fight. I was never able to observe, under the same conditions, fighting between different sexes of individuals in N. vespilloides.

The fighting instinct of males and females has a certain distinction. The female behaves during the time of passage digging in a vigilant, and limiting manner and neglects the digging work more or less. The male however turns exclusively to the work. First if they by chance meet at their work, the fighting instinct is aroused. Then their fight does not differ from that of the female.

The circumstance that temporarily several males are able to be found digging at once on the same carcass, is naturally very conspicuous in the biology and has given occasion to far-reaching, theoretical remarks. One remark by Fabre says that the researcher saw, on average, more males to use the help of pairs, often also the effect of social instinct. "Un couple etait-il dans l'embarras, avertus par le fumet, des aides surviennent, servants des dames, qui se glissent sons la piece, la travaillent de l'echine et de la patte, l'enterrent, puis s'en vont en laisent a leurs joies les maitres de caens". Quite similarly Renkev (1913) interpreted this appearance as "the first germ of an altruistic instinct", while Schroder (1929) in his even wanted to recognize a " particular case of the use of strange foreign expediency".

Alverdes (1925) expressed the presumption the opposite way, that the assembly of several grave diggers at carrion suitable for broodcare showed only "association", in a sociological respect, whose origin lead back to environmental factors, not the existence of social instincts. This explanation neglects the crucial point of the problem, namely the question of what causes the surplus individuals to leave the carrion. So far, however, only the carrion work of the males from my results confirms Alverdes' prediction.

For inspite of the common work which in truth is only based on the chance adding up of single results, in fact no relationship exists between the digging males. Every male works for himself alone and for himself personally. His advantage lies in the chance to reproduce successfully and this possibility is never abandoned without a fight in favor of a competitor. Every male looses much more than every female, first then his place and if it is forced to do that by a mate of the same sex, which is superior to him in strength and skill. Through this therefore, the prediction of Renkers' (1913), as also the explanation of Schroder's 1929, is without foundation.

c. Ecology of the fight.


The main value of the fight between gravediggers of the same sex is frequently that a single pair remains behind at the carrion and their descendants find sufficient food. The existence of the instinct to fight is already sufficiently motivated through this.

But it appears to me that this fighting still raises a further use: An effective choice within the species. This opposes us more clearly in the fights of females. Any female which is in possession of a body has to prove, as it were, before a new approaching female by way of a fight its strength, skill and the normal functioning of certain instincts. Then the carrion passes into possession of the superior animal and so that the possibility of egg laying on the piece of carrion in question remains only for the better equipped female, and obviously encourages the propagation of the stronger and healthier female. While one is allowed to accept that this stronger selection puts the reproduction of weaker or even genotypically retarded females in question.

The translation of these results in the fighting of males with one another however meets with difficulties. While with the driving away of female animals also these germ-cells become distant, when any female first proceeds to egg-laying after the burying of the carrion and these long winded preparations, the numerous males are chased away often first because of the small desire to fight off male animals after they have already mated with healthy females of the same carrion. In such cases their violent removal becomes meaningless as a means of eliminating inferior quality. A cause of selection, through fighting, therefore can be found in the males only in one case, in which the chased male did not succeed in mating. The possible drawback in this for the species made up for through the gain would result from the adding up the work performance of present male at the same time.

This remark "natural breeding choice", which is recognized in the fighting between gravediggers of the same sex appears suitable from consideration to permit a classification in the narrower conception of "sexual breeding choice". Although those fights, at least by the females, determine the permission of participation of individuals in reproduction, nevertheless the lack of connection of fighting animals to the representatives of the different sexes excludes the sexual breeding choice. The fighting of gravediggers is for possession of the carrion, not for possession of females, and males respectively. Any Necrophorus fights only in the direct vicinity of a suitable body for the broodcare. At meetings of the sexes under other conditions, for example of large carcasses, mating pairs are frequently found without observations of hostile attitudes or fights between individuals of the same sex.

d. Fight with strange species or races of gravedigger

Gravediggers are sometimes also ready to defend the stores of food committed to the brood against representatives of strange Necrophorus species. Naturally it gives in easily for in districts with mixed environmental characters several species are attracted to a carcass. Yet fights do not always result from this meeting; the weaker species usually hastily retreats before interacting with a larger species. This is established particularly frequently in N. vespillo and N. humator. A N. vespillo female leaves the prey it has fiercely defended against females of its own species, when approached by N. humator of either sex. Even strong N. vespillo females, which in size are scarcely smaller than weak example of N. humator, retreat, leaving the carrion to a N. humator. Occasionally particularly aggressive individuals of N. vespillo fight against an enemy of a strange species with variable results, as I observed in eight cases. The fight developed then as between the same species, however it went ahead independent of the sex of the two participants. More males and females attack representatives of the weaker species, for example N. vespillo or N. vespilloides, without any hesitation provided that these do not avoid the attack through hurried escape.

A remarkable observation is inserted here. In the surroundings of Frankfurt the species, N. vespilloides shows considerable variation concerning elytral markings. The black crossband which normally goes through the elytra unbroken, slightly behind the middle and often extends so far that the distally lying red yellow crossband, is reduced to two almost round spots, is displaced and in several examples is so strongly reduced that only a row of small black dots or a long line remains between which both red yellow marks come together. There the existing various different kinds of elytral marking show all transitions, missing any possibility which separates stronglv differing forms with the help of named characteristics as hereditary race of the species N. vespilloides

The investigation offered me the opportunity to establish whether really only one pair from a large number remained behind on a buried carcass. I observed that females with strong elytral markings either always paired alone or with a male differing from the norm by the same degree. This observation is based on twelve recorded cases which were all positive. I never observed a negative case, and I can rely on several more positive but not recorded observations. If one considers the relative scarcity of this extreme observation, it appears that it could not be due to chance; one explanation is that the abnormally marked females fight or drive away the normal males and only leave males similar to themselves unmolested. This supposition assumes a physiological difference of those females from the normal which can only be based on hereditary mutation. Then would mention the possibility for it that the weaker differences of all degree is considered genotypical without being isolated physiologically from the stem type. The extremely different form had the value of a beginning species.

e. Course of the fight

After establishing which individuals fight each other we now move towards the kind of fight. The typical fight of a gravedigger happens with such speed that it is impossible at the first observation to grasp in this confusion fast moving legs of individual actions. Repeated observations of the incident supported by instantaneous photographs finally allowed recognition of the real stages of the fight. How quickly the movements were carried out comes from special difficulty of the photographic technique. At first, when the exposure time was reduced to under 1/100 sec the picture received sharp contours. Most were therefore taken with an explosive of 1/250 sec. I operated with "Agfa instant flashes." It offers the advantage that at the moment of the brightest illumination which lasts for the duration of 1/250 sec., the adjusted shutter of the camera was released electronically. The duration of the fight amounted to the quickness of movement corresponding to a few seconds. Only rarely for example with very fatigued animals did it take a longer time.

The beetles usually simultaneously came upon the lip of the abdomen of others scent, began the fight in opposite positions. Next the opponent throws himself at the side and seizes the opposite side of the head and thorax. In this attitude one sees how each of the fighters works the abdomen of the adversary with its mandibles. The closed jaws slide repeatedly from distal to proximal part and bite, where they push off the hindrance as at times on the segmental boundary. To this point the fight still remains undecided. Soon the firm hold of the beetles appears to loosen. Each individual tries to move his adversary with his legs, for this the longitudinal axis is put across its own. If one of the fighters succeeds in this, the fight is soon decided. The beetle which at first squeezes his opponent with his legs, now has an easy match. He presses his victim together many times with such strength that one hears the chitin cracking. The animal which is stuck under the firm grip of the legs in a living vice is unable to offer resistance while the limbs are shackled to him. Fig. 5 shows this phase of the fight with which its end is reached. Again free, the defeated gravedigger takes to flight immediately.

The fight takes another start, if one of the escaping animals, which ought to be withdrawn or a young beetle appeases his hunger on the carrion intended for the brood. In both cases the persecutor tries to seize with his forelegs from behind the last or second last pair of his opponents and these pulled close with a jerk. Here the animals soon lie against one another on their sides. In contrast to the above situation they have an equal tendency to be righted as Fig. 6b illustrates. The rest of its course follows as described above.

Finally still the result of the fight remains to be considered from the individual concerned. The weapons of the gravediggers which are employed in the fight are above all the legs, in particular the last pair, the mandibles being of secondary importance. Although the fight advances on strength and wildness one hears at times loud cracking of the chitin. I have never seen a beetle emerging hurt from it. Conspicuously indeed the comparatively high percentage of mutilated individuals remains, which one comes across at the time of reproduction. Mostly it concerns missing tarsi, sometimes also missing tibiae or antennae. It is also possible that these animals have lost these parts of the body through their difficult digging work; I nevertheless incline towards the assumption that also during the fight, injuries can originate. On the one hand, the observations speak for this interpretation for I repeatedly found injured individuals full ovaries with mature eggs. This suggests that the animals in question probably still had not even dug. Also, the mutilated animals are particularly aggressive; they are more frequently willing to fight the others, especially strange species and perhaps stronger individuals.

A recurring effect of fighting is the speedy escape of the weaker animal which as result of receiving attraction a clear change of behavior can be observed. The digging instinct which rules the beetle up to his defeat, becomes displaced by the flight instinct. In by far the majority of cases the escaping beetles collected in the nearest vicinity in the earth without venturing a new attack during the following hours. On the contrary one sees them either clearly avoiding the body or in their search for a hiding place not giving it more consideration than an indifferent hindrance. Still, the duration of this happening appears to be dependent on the intensity of the sustained defeat.

Undoubtedly the escape instinct supports, so far as it concerns fights between individuals of the same species, the fighting instinct with regard to its biological significance in most favorable ways. Then firstly from the cooperation both results in every advantage for the species which were already reviewed in the last chapter.

f. Relations between partners of the pairs.

That the relationships between male and female during digging are extremely loose has already been said. The fight between beetles of the same sex round the carrion can in effect bring about a change in the pair without releasing a visible reaction to the fight by the indifferent remaining partner . Only the presence of the body holds both sexes together at this time. If the carrion is removed the animals then leave the digging place and furthermore take no notice of one another.

Nevertheless, the following observation allows one to assume an association between male and female: the distinctly audible chirping that the male as well as the female produces with the help of shell organs--most irregularly--arouses an impression now and then, that as if the partners mutually answer one another. In most cases the chirping proceeds in the way that the verse of the animal which is composed of several shrill noises of the same kind start the verse of the partner; schematically it can be represented in the following way at which the number of the quoted shrill noises added is of no importance:

Male ------------------------

Female -------------------------

While this incident in the male is already over after several seconds and repeated first after a considerable length of time, I was able in three cases which were observed completely in the wild, to overhear the loud utterances of the gravediggers which really differ from the first type described. It is a matter of a continuous common chirping of males and females which lasts minutes long and sounds very strange. The unusual sound picture arises that each alternates a chirp of one animal with that of the other, schematically expressed:

Male - - - - - - - - - - - -

Female - - - - - - - - - - - - -

Whether a firm task falls to the chirping of the gravedigger at the digging and which it is, I cannot say with certainty. In all probability the partners influence (perziperen) their mutual chirping in some way. Copulation took place regularly in the course of digging, suggesting that the mutual chirping is an expression of sexual excitement. Moreover the possibility exists that the chirping operates as a warning noise and serves to frighten away related species or genera. The common minutes-long chirping of males and females especially give this impression. It was strengthened owing to a pair chirping in this way being constantly in regular activity: while the male digs one frequently sees the female radiating from the prey, going out investigating.

As soon as the digging work is thriving over the first start, the mating happens above ground. The male climbs the female in a manner that in normal important relations his foretarsi get a grip of the corners of the shoulders of the female and the middle tarsi grip round roughly the epipleurons. During the actual union of both beetles the male performs a brushing movement with his foretarsi which appears broadening in relation to the female. At the end of 3-4 seconds copulation is terminated. That same pair can however still proceed to renewed mating before the conclusion of the digging work.

2. Relations of the beetles to their offspring.

a) Brood care

Examination of the food selected for the brood. As the gravediggers are not choosy concerning their own food, they are also satisfied with any carrion for the provision of the brood. Indeed the size sets the upper and lower limit. Beetles are not able to bury large pieces and small ones do not supply a sufficient quantity of food for the numerous hungry larvae. However, between those there remains considerable latitude. If we disregard the strongest member of the genus, N. germanicus (this species is rare in the surroundings of Frankfurt and so therefore too small for experimentation) carrion from the size of three day old kittens to pieces of meat 1 cc were buried. They were usually distributed such that N. humator naturally found the largest, N. vespilloides the smallest pieces.



Unable to detach pieces from large carrion, the beetles are directed in their care for the offspring predominantly to the bodies of small vertebrates. When a sexually mature gravedigger has located a carcass, he first reacts in a wholly determined way. The dead body is climbed, the mandibles beat here and there loosely in the carrion with the maxillary palps clearly shaking, the antennae moving in a swinging motion. At least twice the beetle steps in nearly vertically one upon another, standing directly on the body. Thereupon the beetle slips under the carrion and its activity can only be guessed. He raises the prey a little from the ground.

The single phases 1. Examination of the find with mouth parts and antennae. 2. Inspection of length and breadth. 3. Lifting of the carrion, take place in succession, being constantly observed before the beetle begins the real digging work. One gets the impression that the animal deals with the act of examination of his find in this capacity. It is conceivable that initially after the find through each constantly recurring action the chemical condition, size and shiftability are examined, thus first from the determined combination of doses of excitement, the digging instinct is released. A confirmation of this presumption is seen in the fact that a Necrophorus not once attempted bury carrion whose size exceeded his capacity.

b. Burying of a body

Naturally the direct observation of the digging activity was impaired to a large measure because the largest part was carried out in the soil and therefore remained invisible to the observer. This circumstance explains why the analysis of the digging technique of the burying beetle is still outstanding. In order to be able to follow the occurrence without a break the investigation must be completed in the wild as such under known artificial conditions. To this end, sexually mature beetles were brought pairwise into narrow terraria to dig so that a direct observation of the activity was possible through the glass walls.

The terraria (24 cm long, 18 cm high, 2.5 cm broad) have wood borders on the narrow side-walls which are cut crossway square (2.5 cm x 2.5 cm). On this wood border is screwed, from below the soil on the long side, a right angled aluminum strip. The long walls consist of glass. Each glass plate leans on the right as well as the left woodborder so that every time

they are attached through one of the outer sides of the wood border and held by the right angled aluminum strip underneath the glass plate on the ground is a prop. Both long walls are held so tightly only by the metal strip that they try to slide slightly here and there as in a rabbet. This is implicitly required in order to be able to change the glass plates during the observation without strong shock. That often proved to be necessary against the work of the beetle held together dirt through small soil particles or carrion. The vessel top was closed with wire gauze.

However, under these conditions which differ strongly from the natural, some of the beetles did not set about digging, but rather exhausted themselves through continuous attempts to escape. In order to be able to use these animals for experimental purposes, I attempted a further trick. A box of zinc plate was made of the size that therein holds the glass vessels put against one another, tightly. All single cages were filled full with soil and above that still a 2 cm thick layer of earth spread out. It originated in this way a roomy surface under which the glass terraria lay hidden. At the start the beetles were in no way confined to their work. In due course they came across the glass wall in the soil, but this hindrance meant no more then a stone or a hard root in the wild which the animals are able to avoid.

Actually all gravediggers went nearly immediately to the work. They fall on the way in the depth with their prey necessarily in one of the glass boxes which then with help from the earth surface over-topping is raised out and the observations made. The glass cage being used was replaced immediately by another, and consequently the described experimental order is ready for use so long as it does not lack sexually mature beetles.

If a beetle found a carrion which proved after complete examination to be suitable then the digging work began. Next the beetle scraped more soil out from under the body. The gravedigger thereby proceeds so that he carries soil particles from behind with forelegs which is further given to the second pair and then reaches the last. From there the strong hind legs shove out the mass from under the body. Though frequent repetition of the activity arises the already mentioned small earth wall of Fabre (1899). However the dead body is not ring-like, but only grasped round partly. Correspondingly, only a part of the carrion is also only dug under.

More frequently than on bare, soft ground the gravedigger finds the carrion on hard leaf. This is especially true for the the meadow-inhabiting N. vespillo. Under these conditions are experienced the application of the already well known (Fabre 1899) ability of the beetles to cut through grass and roots with their mandibles. If one perhaps removes the small animal body an hour after work begins, one sees an approximately round place on which the grass stalks are pressed on the sides and are bitten through the base so that from the small area all sort of roots still travel through, laying free in the soil. The size of the prepared place always is dependent on but, importantly, smaller than the object to be buried. Therefore, also in this case the whole body is not dug under.

From this stage onwards the digging work is continued independent of the existence of a ground covering always in the same way. Even after the

number of hindrances which it rescues from the ground in the shape of roots or small stones, it merely fluctuates the working hours. The beetles push out more and more soil from under the carrion and thereby deepen the already started hole without broadening it at the same time. The part of the body which is dug under begins to sink under its own weight (Fig. 8a).

Up to this time one is able to follow the work of the Necrophorus from the shaking of the body, then suddenly this ceases and remains completely motionless for a long time. Through that the observer receives the impression that the animal has ceased its activity, but in reality the work goes ahead briskly and is continued in another way. The working animal has begun from the hitherto cultivated, shallow depression to dig out a passage sloping from beneath in the soil. There the diameter of the hole behind the original cavity falls behind with its increasing length more and more so an automatic after sinking of the body does not come into question (Fig. 8b). By this it appears that it is able to arrive during the work of the beetle with no shaking of the body. As tools for the digging of the pit, the animal is served principally by legs, which forward the soil in the already described species and manner. Now and again one also sees the gravedigger push large lumps of soil with their neck plates.

The newly excavated cavity reached finally a length of 3-4 cm, with very small carrion from about 2 cm, so begin again a new phase of digging activity. The carrion now becomes forced into the prepared hole. This represents an important achievement for the beetles. For the body must be brought to a small volume, otherwise it does not manage to pass along the narrow passage. The start of this working phase the beetle orients itself under the carrion so that its back is turned towards the underground, the abdomen tip towards the newly excavated, funnel-shaped hole. The animal now grips the body with the tarsi and hauls it in with accurate movements of the legs from behind and like-minded movements from the head and thorax over itself off deeper into the hole. In most cases, the gravedigger grasps the carrion in the middle, and pulls it into the passage while the LAST SENTENCE CUT OFF WHEN XEROXING! this way, out of it the advantage results that the carrion is pressed together in a very much concentrated mass. This is the first step in the rounding of the body which is experienced later in the crypt. The more the carrion squeezes itself in the slope in the cavity leading to the funnel, the more effective the effort of the working beetles which in order are firmly it refutes gains on the funnel wall.

How successful this working method is, is shown by a chance observation. A N. humator female buried a piece of horse meat some 6-8 cm in a sunk flower pot filled to the higher edge with earth. By aiming at the base of the vessel, the female pressed its find through holes in the base of the flowerpot which were big enough to allow through the N. humator female a small example. By digging up the pot, the meat was held tightly only still with a small point, while the remaining part had already passed the narrow opening. Only with difficulty did I succeed in pulling back the meat the same way with forceps which is able to give an idea of the working capacity of the beetle.

Still before the carrion has arrived at the end of the prepared passage it is extended in the beginning successful way. Fig. 8d. Scarcely does this happen round a tiny piece, so the animal shoves itself along between carrion and soil and walks round the prey and in doing so gives it the advantage of a smooth body shape. In this way all parts of the body become dragged here which still stick out of the main lump as for example tail and legs. Thereby the whole carcass is stuck together more and more. Fig. 8e. Both activities, gradual lengthening of the passage and hauling back the body with rounding off at the same time, alternates at length with one another till the carrion has reached a certain depth. The thrown out material is, as already Fabre (1899) observed, in the meantime thrown together. Only a small soil accumulation free of plant growth betrays the activity of the gravediggers.

From the given description one presumes understandably that the carrion is not vertically under the small hillock. Moreover, one regularly finds several centimeters laterally from the small heap, loose earth distant in the soil (Fig Bb), an establishment, which again allows a conclusion about the working method of the gravedigger that through digging under the prey alone would hardly succeed in this place.

In the same way as N. vespillo goes about its work. so too does N. humator, N. germanicus, N. investigator and N. fossor; N. vespilloides is an apparent exception. This inhabitor of drier woods buries his finds only under mosslawns, leaf or needle litter which puts plenty of living room at his disposal. His performance confines him thereupon to carrying the body through the often several cm high ground covering till the carrion is put on free earth. If one finds such a buried carcass, one can be certain to have the work of a N. vespilloides, Fig. 9. The instinct of this species is so well adapted to the normal conditions of his environment that N. vespilloides in a cage without ground covering is very rarely brought to reproduction as I was able to experience with my experimental animals. However as soon as one puts plenty of moss or needle litter in the rearing cages, they are no longer opposed to the natural course. Thereby showing that the different phases of the digging event, which were observed in the work of the other species in the essentials are also the same in N. vespilloides, only on account of the loose condition of his materials differing in appearance.

A proof that the above described manner of digging is not confined alone to the named native species, is given in an observation of Osten-Sacken (1862). According to him, N. americanus ought to produce a long sloping in the soil leading to a pit in which he slips in the carcass. There this beetle ought to be instructed in the main point of snake carrion, Osten-Sacken considered this as he believed from that of other species, differing in digging method as adaption to the shape of prey animals. However this assumption was invalidated for other Necrophorus species proceed independent of the shape of the body likewise. Then the extension of the prepared hollow with increasing size of the buried object takes root, becomes understandable if the long passages which are manufactured as a rule in N. americanus to the taking up of snakes, is seen, while they were able to ignore decidedly shorter cavities in the native gravediggers average for small carcasses.

The depth up to which the gravediggers bury their finds, varies with the species. In some 60 cases the distance of the soil surface vertically to the roof of the crypt was measured. Thereby proving that N. germanicus digs the deepest. This species was only observed in captivity however, in which the animal moved the carrion without exception to the hottom of the cage which was 20 cm deep; it is possible that this animal reaches greater depths in the wild. A buried carcass of N. humator was found normally at 7.4 cm depth; the highest measured value for this species amounted to some 13 cm. In the smaller interval from the soil surface one finds the brood holes of the remaining species.

The time which the burying of the carcass requires is dependent on the size of the object, on the condition of the ground of the physiologica competence and finally the number of working beetles. The following observations which refer to a female N. vespillo give an idea. The animal had carried a mouse in loose garden soil, with peat mixed through to a typical depth for the species N. vespillo in 3 hours. In natural conditions in which a turf is penetrated through, roots and stones are dealt with; this work takes up 8-10 hours in the above described narrow glass terraria the beetles required likewise a whole night during which several long rest pauses were observed. If several gravediggers take part in the work, so the working time shortens in proportion to their number.

c .Rounding of the body and completion of the crypt.

One finds clumsily formed balls of carrion after the finish of the digging activity in the ground. Fig lOa-f. show carrion taken from the crypt. From all forms shows the instinct of the beetle to adjust the carrion as far as possible to a ball shape. The skeleton of vertebrate animals frequently resists the rounding; from figures lOb and c this problem is obvious with a bisected frog. Boneless pieces of meat which can be shaped anyway by the beetles keep a perfect ball shape well. The expediency of this round form is obvious: with the smallest surface area the ball protects the largest volume and therefore is particularly favorable to preserve the food from desiccation.



Rounding of the carrion and building the crypt are closely connected in their origin, and arise as a result of one and the same activity. For hours on end the beetle wanders round the buried prey step by step in all possible ways. With its feet on the body and its back against the surrounding earth, he lifts the mass continuously through stretching of its strong bent legs away from itself. Through the counter pressure of the soil which opposes the back of the beetle as well as the opposite lying side of the body, the carrion is strongly pressed together and obtains the ball shape from the constant repeated kicking on all sides unless the strong skeleton resists it. Necessarily through the constant pressure of the surrounding soil, a cavity arises with hard walls in which the fully rounded animal body rests. It is the crypt. The diameter is dependent on the size of buried object as well as that of the working beetles.

As was recognized already by Fabre (1899), one finds the small mammal's bodies hairless, the bodies of birds featherless also without tail or steering feathers in the crypt. How this appearance ought to be explained, as though the results of wind decay or as the result of active work of the beetle, Fabre left open. However, none of these possibilities alone give the truth; first through the interlocking of both factors arise several admitted results. Through the ungentle treatment which the body receives during the digging activities in the passages of the narrow cavity on the one hand the sedimentary hairs or feathers which are only still loose in the skin of the body, fall out without direct action of the beetles; on the other hand the animals subscribe directly to their removal: after rounding the body and at the same time completing the crypt, the beetle continues to walk round over the carrion, however with renewed activity. Like a spatula its head now stretches with slightly open mandibles over the surface of the ball and free the food provisions of particles for the larvae and also still attached hair or feathers. For hours on end, only broken by short rest pauses, one sees the beetle performing these movements which are brought about through bending in of the initial thrusting out of the head. In this way every square millimeter is cleared stepwise--apart from direct observations--as is recognized from an enormous quantity of tiny points which were left behind by the mandibles in the soft substrate and which by now cover the whole carrion ball. The falling away--be it hairs or feathers--gather on the base of the hole and there become pressed against the walls of the brood rooms by the gravedigger so that he covers them with a carpet similar to the base of the crypt. This was observed at its most perfect on carrion which were buried in soft peat, free from all hindrance. Under the conditions which in the wild are most frequent, one finds traces of hair or of feather which have been lost for the large part already on the way through the firm soil.

d. Egglaying

When the carrion is rounded, cleaned and resting with a smooth surface in a firm-walled crypt (which to reach this portion of necessary activities requires in total between 12-48 hours) the female proceeds to egglaying while the male repeats from time to time the above quoted work.

As first Hain (1927) and V. Lengerken (1928) have stated independently the eggs of the gravedigger are not layed on the carrion or in the carrion, but individually in the soil, as I likewise confirmed. Unexceptionally I found in more than 100 cases, the eggs of included species, singly in small earthholes which show a striking arrangement. They lie, as I was able to observe in the species N. vespillo (76 cases) in some 6-10 mm intervals to both sides of a round shaped, smooth-walled against shock, indeed little resistant passage which the mother animal has dug from the crypt out into the soil. It is analogous to the parent gallery of the barkbeetles, a space is quite big enough to let the female move through it unhindered. The passage runs horizontal with weak bends to the crypt in the soil (fig. 11 and 12). Its length depends on the number of its flanking eggs, whic in N. vespillo can fluctuate between 1-24, but averages about 14-15 eggs(Table 3.)

The small chambers in which the eggs lie, are built in all probability through the activity of the extended laying apparatus of the female, which releases frothy drops of secretion at the same time the small hole receives an egg. The barrel shaped eggs are white and shining. The size directly after egglaying, an average of 2.958 x 1.836 mm, a result which was calculated from the following values (table 4).


e. Moisture and digestion of the body

After egglaying the female hurries back again to the crypt and moves the pile of earth from building the mother passage to the side while it wanders round the carrion in the explained way and presses the loose earth to the wall. This as all previous earth working of the gravedigger requires for success a certain moisture of the ground which the animals find in the wild at their living places and which is carefully supplied in the terrarium.

After the hole is tidied up, the female begins with a remarkable activity: at the highest point of the carrion ball the animal digs a circular hole which on average measures 1/2 cm in diameter. First the surface of the body is bitten to pieces with the mandibles then the fore tarsi grip extended into the gaping split. With help from head and forelegs which represent, with the strong tibial spurs, excellent instruments, the cutting circle is pulled apart as with hooks so the opening enlarges to a small crater. In this hollow the beetle lowers its head and begins to eat, as is concluded from the movement of the mouthparts. It is the first meal taken from the buried body. This was certainly not remarkable for an eating place and was found repeatedly at the corresponding point of every carrion ball and at the same time. The place was at that where later the young sliding larvae gather. At the end of about 1/2 hour the beetle appeared satiated. Still she never moved away without shutting the hole and finally smoothing the surface for a long time with the underside of the head. In fact this precinct in no way differs from her later surroundings. The excrement of the beetle, after completion of this work, was distributed now on the upper half of the ball. The animal which put the anal opening of the carrion surface to this purpose, proceeded slowly over it then while the abdomen carried out a sideways pendulum movement in this way the liquid excrement succeeded in making a snake-like track on the carrion which is recognizably shining with moisture and first disappears after some time through blending.

In the change with hours of peace which the animal spends pressing tight the meatball, this work fills up the period in which the brood passes through embryological development.



The question of whether this instinctive action is of use for the descendants ought perhaps to be answered in the affirmative. The smearing of the liquid excrement on the ball of carrion doubtless serves the use on the one hand that the food provisions, already protected against the danger of drying out to a certain degree by their shape, remain moist with greater probability as this then also found, always independent of the weather, moisture glittering in the crypt. On the other hand, for this reason, it is possible for the carrion ball to become dried through with the scent of animals which, is demonstrated in return for our ability to smell the gravedigger in the excrement. Be it that the Necrophorus scent acts to scare away other likers of carrion or also the attraction of the small larvae which emerge from the egg scattered in the neighboring soil, which would also conceivably be an advantage in this respect.

But also the taking up of food of females represents an action of broodcare. Presumably, if the already previously mentioned supposition of a preoral digestion of the gravedigger is right, the food begins to decay with the feeding activity of parental animals sharing digestive enzymes with the environment. Thereby, the crater becomes deeper and deeper with the passing of time on the inside of the ball of carrion and the female renews the deposition of fresh secretion which accelerates the otherwise slowly advancing process.

That it is a matter of the disclosed consideration, not pure speculation is proved by the behaviors of the female several hours before the brood emerges. At this time the up to now calm movements of the animal become hasty--nearly abrupt as at the end clockwork. The ball of carrion hurriedly climbed on and the eaten area opened with impetuous movements of the head, which allow the onlooker to suspect rapid destruction of work. Without turn, as hitherto again to close the beetle now walks through, in many cases softly chirping, the mothering passage from which it turns back to the crypt after several minutes. After the beetle has walked through the whole subterranean cavity one soon finds her sitting and eating again on the ball of carrion at the crater thereupon arranging the opening in a regular circle. This activity of the female which coincides roughly with the end of embryonic development in the brood, is closely connected with the appearance of the descendants. The fact that the crater is opened at this time and is no longer shut, proves that external digested food is intended for the larvae. The walking through the mother passage which is repeated several times in the course of 20-30 minutes is suitable for facilitating the hatching larvae in the soil in finding the carrion. On the one hand the scent of the female makes it possible for the larvae to orient better, on the other hand the beetle roams out in the space of passages, throwing pieces of earth. Thereby the young larvae opened a way in which they are successful in obtaining a quick and certain food source.

f.Male participation in brood care

Brood care is independent of the sex in sexually mature gravedigger. Every male just as every female, is able to bury carrion as experiments in which the sexes were isolated have shown. Observations in the wild are however in contradiction to this result. Males which set about the digging work without the presence of a female stop their work after a short time in order to attract a female through "ventilation". If there is no result, the carrion remains uncovered or buried only shallowly. This indicates the dependence of the male on the presence of the female. We verify this supposition with an observation occurring when a female was removed after termination of the digging activity and the male was left alone. In this case the body remained unaltered, a fact whose meaning is unmistakable. A mistake by the female affecting the brood and long preparation of the body would cause a significant loss of time. The pair remains together so that the male participates in all the females work. However, in the majority of observed cases the male left the crypt in the interval between egg-laying and the hatching of the descendants--either of its own free will or in the face of a hostile attitude from the female. Only exceptionally is the male still found together with the young brood, perhaps because the female is not always successful in driving the male away. However, N. vespilloides males are the exception to the rule because males are found with broods in nearly half the cases.


Fabre (1899) supposed that after preparation of the body for the brood the pairs left the crypt. The majority of obtained observation in the wild oppose this (Table 5.) In the woods and meadows in the surroundings of Frankfurt suitable carrion was laid out for burying. Roughly 48 hours later I visited the same place and noted which carcasses were buried by the gravediggers which was recognized by the slight but typical alteration in the ground. After a further 7-9 days during which the building of the crypt, the preparation of the carrion is completed the larval development must be more or less advanced, the broodrooms were cautiously opened and the finds resulted as follows--table 5.

After the combination the larvae from I to III are to be found and the last stage nearly always in the company of a pair or single female in the crypt. The moderate number of exceptions (4 out of 59) lost most meaning when one thinks how easily the results could be negatively influenced by digging.

Also Fabre once found by opening a crypt of a Necrophorus pair together with the larvae. This observation which contradicts his acceptance that the parents shall leave the crypt before the hatching of the brood, he explains in the following way: "La periode de la parse est maintenant fise, et la victuaille est copieuse. N'ayant pas aube chose a faire, les romanicus se sort attables a cote des noumsaous" Fabre (1899). The view arrived at in this quotation that at the end of the brood period many parents stay with the larvae on the carrion merely to satisfy their own feeding requirements has till today prevailed. Through my establishment that the parents, above all the female, are found regularly and during the whole breeding period in the company of the larvae, this is refuted. But this presentation becomes entirely valid, if itself restricted a close relationship between the female and her descendants is disclosed over the care of the brood. Was the species already as the mother attracted the scarcely hatched larvae, already unusual in the beetle order, thus excelling in the activity, which happens in crypt between the female and her brood all that one knows up to now in this respect about indigenous beetles.

The following observations were described using the cage in Fig. 7, a glass cage which made insight into the crypt possible. After completion of digging activity the cage was brought from its vertical position to a side position, so that the beetle was given the necessary room in the horizontal to build the crypt. The larval nest was drawn from the natural brood room and brought together with the pursuing female into a small flower pot, which was shut from above by a damp cloth. During the observation in softened light this was removed or replaced by a glass disc so as not to disturb the female. Before I was able to turn towards the mentioned activity the brood must be accurately taken into consideration.

g. The brood at the time of larval development.

In the extraordinarily small time interval of 7 days for the development of beetle larvae, the necessary weight and size increase of Necrophorus larvae to form the adult occurs. The speed with which the development proceeds becomes more astonishing if one takes into consideration the achieved performance of growth in this time. While the increase in length which normally is in no way exceeded (the N. vespillo larvae grow an average from 0.5 to 2.8 cm), the increase in weight is in proportion to developmental time. The enclosed curve Fig. 14, whose values were obtained through daily weighing of the larvae with the help of a Sarbornis weighting analyzer, gives an insight into the weight increase of three N. vespillo larvae during the 7 day developmental period. On the X-axis is the age of larvae - calculated from the moment of hatching-stated in hours. The Y-axis bears the weight in mgs. The first weighing was carried out immediately after the hatching and before the first feeding and was for larva I 0.0035 g. After 7 hours the starting weight had doubled. The last weighing took place shortly after the wandering of the larvae from the remains of the food carrion, and showed for larva I 0.3037 g, where afterward the total increase in weight was roughly 100 times the initial weight.

Disregarding the statement of absolute values, the graphical representation gives us information about the rate of increase of weight of age stages. Two rapid molts H1 and H2, separate the three larval stages I, II & III from one another (Fig. 15 for N. germanicus.) Larval stage III not only takes up the longest time in the larval life of Necrophorus, explaining why one encounters mostly larvae of this age in the wild but also has the greatest rate of increase in weight, which probably during the first 48 hours was somewhat held back through the energy consumption in the ,short interval following moulting. The drop in the curve towards its end (from L1 from 0.3573 - O.3037 g) has a double cause. Firstly, the larvae cease feeding shortly before leaving the crypt and more importantly they empty their previously full guts.

The three larval stages, which do not significantly differ with regard to morphology, can be recognized through certain clear differences in their behaviors. At the end of embryonic development, which takes 5 days, the larvae of the grave digger hatch from the egg. In order to free the sticking egg cover from part of their body, the animals try with intaking movements of their longitudinal axis, in which they succeed in about 1 min. Thereafter the egg chamber is left immediately and the larvae walk to the stored up food. The newly hatched larvae are white, very agile creatures, which with the help of six legs and their hind segments which function to push behind, move away smartly and restlessly with antennae held upwards. The majority break through the earth-layer which separates the egg chamber from the mother passage following the leveled path of the female and reach the crypt in this way in a comparatively short time, where they are attracted to the scent of the carrion and that of the female. Single individuals also try to succeed directly through the soil by the shortest route to the provisions of food where they likewise succeed. Indeed then the small larvae require 2-3 hours to cover a stretch of 4-5 cm which it does in constant motion, only stopping for a few short rests. Every small stone poses an obstacle to advance and must be gone round, till finally the animal falls into the subterranean crypt by shoving through the crypt wall. At once it climbs the ball of carrion to the highest point and there enters into the crater together with its brothers and sisters, which follow the same instinct to the same place.

That the freshly hatched larvae, in fact react chemotactically to the smell of the carrion which forces its way through the mother passage and the soil to them, is shown by the following experiment. A wall of carrion taken from one of the crypts was laid on a piece of filter paper and the center formed a circle of 25 cm radius from the periphery in regular formation were distributed 10 N. vespillo larva of the first stadium. Each larva was covered with a small glass dish under which they were free to move and could be put in any course. The experiment was carried out in a room in which no noticeable air current was recognized. The illumination of the otherwise dark room was done with a lamp with strongly diverted light. After lifting off the glass dish all 10 larvae wandered in roughly circular courses to the ball of carrion. Thereby with the exception of 6 larvae, all experimental animals appeared at the carrion after short searching movements in the direction, which on the whole were detained. Only 6 larvae initially moved themselves in the opposite direction in order to later hurry to the carrion in nearly straight movement. In the immediate vicinity of the carrion they met several larvae. These came to the residence shortly, whilst these move round one another, making their separate ways without exception to the source of the smell. The required times for the ten are given in the following table.

The experiment was unsuccessful when repeated with larvae III. Then their movement resembled a random walk in various directions which took the larvae away from the carrion, as well as toward it. Often the smell of the carrion was not received by these larvae over large distances, although when in the immediate vicinity these animals appear to be able to perceive the carrion and walk into it.

The aimless wandering around, which restricted the experiment involving older larvae, caused the animals to meet frequently. Contrary to the behavior of larvae I, larvae III remained closed to one another when they came into contact; frequently they were attracted by their own smell of carrion. This behavior gives rise to a cluster of larvae, which is in constant motion through the circling around one another of the larvae and as a whole rolls slowly from the place. Fig. 16 shows one of these groups of larvae which originated in this way. Although in this experiment the food is only 9 cm distance from the larvae heap, the animals remain crowded together, till after an hour the carrion was put back 2 cm distance. First in this moment the closely pressed group loosened and the animals clambered singly onto the carrion. This observation shows for the first time that the old larvae are attracted to the smell of carrion only from a short distance, in striking contrast to larval I stage.

With increasing age of larvae, weakness of the ability to smell can occur in connection with the altering condition of the larval environment. Thus the needs of the larvae correspond throughout but the problem of finding carrion from greater distances falls to the young larvae; larvae II and III suffice with the kind of attraction which holds them together in close combination with the food.

The portion of the ball of carrion from which the attraction radiates is the higher pole, prepared by the parents, with intestinal secretion to form the crater. Here the young larvae appear and the old larvae remain. From here the consumption of the carrion starts. How this takes place is again remarkable. While the brood are in stage I and II they contribute, through their feeding, to the broadening of the crater in which the young larvae lie horizontal in the casing with their heads pointing outwards. Soon the larvae advance to their second moult inside the body. They rummage about and feed themselves deeper and deeper into the carrion. As long as there is no lack of food during the 7 day development, instinct allows the larvae to leave the outside of the ball of carrion undamaged -indifferent to conditions - so that they finally rest in a nest with both shelter and food. In the wild in which the grave digger directs in his brood care on small bodies, the center layer is formed from the skin of the corpse giving mechanical protection against advancing robbers. The rounding of the ball therefore retains also the shape first bestowed on him. presentation is given in Fig. 17 of how the larvae are able to disappear into th depth of the body. If the provision of food for the brood is less plentiful than in the quoted example, the larvae are not able to completely conceal themselves. They then put only the front of the body in the carrion, while the hind end remains visible (Fig. 18).

The larvae II stage is also found if the ball of carrion was big enough for them to allow a scattering of the larvae inside its mass, nestled uniformly crowded with one another. It is true the appearance was able simply to be gone back on, that the larvae from a close undescribed precinct from the crater in which they lie close together, begun the advance into the ball of carrion. The following observations however give us the right to perceive in every appearance the utterance of a particular instinct.

It appears namely that larvae III are qualified for the pursuing of oral drips : if one lays a larvae in a cupped hand, they leave every where small brown drops where they touch their closest surroundings, tasting with the head. That allows conclusion of extra intestinal digestion. It appears that the quantity of preorally digested food I suppose is used for the young larvae not for the older brood. If however the larvae III really digest preorally then it is able to be of help to the animals, if they press together with their heads in a small circle to feed. Why?

We start from the condition of an isolated single larva. The deposited digestive secretion from it is pressed constantly in all ways loses very soon with distance from outlet point the required concentration for effectiveness, through a certain part of the digestive secretion going for the conversion of food. Otherwise by some sense pressing together of the brood. Now the resulting fall in concentration from the oral drops of each larva overlaps with the original fall in concentration around the quantity of secretion of the neighboring larvae. At the place of overlap however much too small quantity of enzymes reach effective concentration to be able to contribute in this way to the quick formation of the food.

This presentation finds yet further support in the fact that one finds also other extraintestinal digesting insect larvae in the same group. Larvae of Miastor metraloas were found to lie radially, the head reaching from the middle of the circle, by Springer (1917) who showed the above mentioned advantage in their position.

If, however, the habit of remaining bundled together of older burying-beetle larvae is an advantageous instinct, it is doubtful through which kinds of attraction they would intervene. It maybe a matter of mutual thigmotaxis of the larvae. It is possible that the ball on the

outside of the carrion ball happens in older larvae is not explained merely as a reaction to the outgoing attracting smell, but from mutual attractive contact playing a part. The thigmotactic attraction of the larvae prevent in a suitable way any dispersion of the animals. Actually it is extremely rare to observe a larva leaving the nest prematurely. Only from time to time one can surprise the larvae as they hang their hind ends far out from the crater edge, Fig. 19. This is the attitude which the older larvae maintain for defecation. The emerging pellet of excrement falls off on the outside of the ball of carrion containing a mixture of food and excrement and with that prevents a reduction in the nutritive value of the carrion and at the same time strong soiling of the larvae is avoided.

Further, a most remarkable instinct of the larvae should now be mentioned in the next chapter in connection with certain instincts of the mother and the parents respectively.

h. Feeding of the larvae.

Soon after the first larvae hatch and have appeared in the crypt the female employs the attraction of the brood from the mother passage and makes for the ball of carrion in which the larvae lie thickly pressed in the crater-like cavity. In permanent motion they crawl over and through one another. Their mouthparts touch the carrion - but only tasting. They never eat from there; the transparent gut remains empty. One gets the impression that the lengthily prepared substrate will be in no way be the searched for food of the brood.

Immediately however the observer presents himself with an unexpected scene. Scarcely has the female approached the crater when all larvae lift up the front of their bodies steeply, so that their legs grasp in space. The beetle remains standing directly over the brood and waves her forelegs with shaking movement on the carrion or sometimes on the larvae, which flock round her head. Now the female closes her mandibles and rapidly lays the head of a larva between the jaws itself pressing closely to the mouth opening of the female. If allowed the chance, then one sees a tiny drop of brown liquid on the mouth of the mother in which the larva infringes. But already after a few seconds the female turns and immediately tries to reach another larva with his mouth held high. Without doubt, the brood is fed by the female. Correspondingly the initially white, almost see-through larvae after contact with the mouth of the mother become dirty brown, a change which gradually progresses from the front right to the hind end of the larvae.

However, with what does the female feed the brood? Is the food source the gut or a specialized gland. Specialized glands, which are rare in beetles, was not found, the feeding juice is derived from the gut. The administered substance is also-gut contents presumably a mixture of food and gut secretions. In fact, the female takes several feeds of carrion at the crater shortly before the appearance of the brood. The quantity of food taken up must be exhausted with time both from feeding the larvae and from feeding the beetle itself. To continue the activity of feeding for several days, the female is compelled to fill the foregut anew. With increasing age of the larvae, the female fed with increasing frequency immediately before passing food at the crater, an activity which claimed up to 1/4 hour.

The feeding can be observed during the first 48 hours of larval development, but is seldom repeated later when the brood gradually are made independent. The young larvae beg impetuously for the food juice of the female. Three to four larvae often reach her at the same time crowded before her mouth and dispute their right against each other to this place. Fig. 2, which allows a glance into the inside of the crypt, shows directly the feeding of highly erect larvae. A second is attacking to drive away the first. Larvae which by chance find the hind end of the beetle, climb about carelessly as if searching for the mouth. Most however, immediately set out for the head of the female. Either the larvae leave the crater to this purpose, in order to lay back outside themselves hurriedly the prey or they make their way along on the ventral side of the female. Here by the larvae showed themselves, lying on their backs, forward under the beetles and more likely did not rest till their mouths had found the provision of food. Fig. 21 shows this frequent performance. Rarely and only in the Larvae I stage one catches sight of an initial attempt to reach the mouth of the mother, namely from those forelegs held out. However, what I saw never led to the result: The small animals clambered with great skill onto the tibia, and lifted themselves with their sucker - like after segment onto the femur. Stretched forward, one then sees the larvae searching for the mouth of the mother.

Fowlers declaration (1912), which characterized the larvae of the grave digger as inactive maggots, is then in no way correct for the young larvae. However, larvae were not constantly attentitive to females. Moreover, a pattern of use and disuse develops in relation to the molting pattern.

Newly hatched larvae are apparently completely dependent on the female for food. They beg extremely impatiently and follow the female for short distances over the carrion with great dexterity and ability. When the young brood scatter themselves even more often over the upper surface part of the ball of carrion, they gather again in an even shorter time in the crater as soon as the female turns back there. At the age of 5-6 hours the larvae then begin to feed independently. With heads turned outwards They lie close to one another in the crater. Their mandibles, whose points have meanwhile colored light brown, beat continuously in the carrion. These larvae are still ready in the vicinity of the female to receive food, and will act as in the first hours of life. Yet they rarely attempt to follow the mother in her walks around the carrion; rather they use her absence in order to eat independently. Also they stay permanently on the inside of the boarder of the crater until the first moult.

Rarely is this executed so the larvae arrange themselves again searching upwards, without also only undertaking an attempt to take up food independently so behaving just as in the first hours of life. After the first moult there is a second period of greater dependence on the female followed, 2-3 hours later, as in larva I, by greater independence. After the second and last moult the larvae is directed in feeding by the parent, in order to quickly complete female care, and finally to grow completely independent.

Conditions during the feeding time, which stretches roughly over the first 60-72 hours of larval development, are summarized in Fig. 28. The ordinate shows the changing dependence of the larvae on the female for food. On the abscissa is marked the moment of hatching, the first and second moults, and the end of the feeding period. Three peaks show that the time span is distributed over three periods in which the brood taxes the female for food: after hatching, and after their first and second moults. Between periods of greatest dependence on the female the larvae feed independently. The female accomplishes certain typical repeated instinctive actions during the entire feeding time in the interval of 10-30 mins. she appears at the crater. The female usually starts feeding, by moving her first pair of legs, comparable to a running on the spot. It appears similar to (The "Mittern") an alarm signal as a sign for the brood to begin feeding. If this hypothesis is correct, the Mittern ought particularly to be for the older brood, hidden deep in the carrion, can be attracted through quick shock waves. In fact the larvae III which are of no further interest to the female also appear at the food after the Mittern, if they have not already outgrown motherly care in this respect.

 
After the brood is alarmed the female proceeds immediately to feeding. The most remarkable of the activities has already been revealed, only a little still remains to be supplemented. The female's pose during feeding, varies, depending upon the most favorable height for the begging brood. While she bends deeply to young larvae, her head and neck plate show a strong inclination downward, the long axis of the body climbs forward moving around to feed the higher reaching older larvae. The weight of the female rests in this position on the last pair of legs. The forelegs are either free and used to ward off obstructive larvae or grip the tails of larvae being fed (Fig. 20). That the female holds tight to the larvae on this occasion shows in the following chance observation. An N. germanicus larvae III was successful in begging for the food juice of the female at the edge of the nest. During the feeding they fell down. The female, continued to feed the larva which was lying on its back held tightly between the female's tarsi. Indeed, this pose of N. germanicus is nothing exceptional; they often take up other poses in the consumption of fly maggots.

The length of each feed to a larva, which was measured by the period in which the head of the larva rested between the mandibles of the female, is small. In N. germanicus the feeding of older larvae can claim up to 18 seconds; but for all Necrophorus species including N. germanicus, feeding times are generally 2-4 seconds and not longer than 7 seconds. Feeding is terminated by a scarcely visible sideways movement of the female's head. The mouth of the female consequently slips from the larva and becomes free for another larva. Five to six individuals are fed in immediate succession. After a break the female again begins feeding exactly the same way. The larvae of a nest are provided with roughly the same amount of food juice from the female. This is the suitable succession of a typical feeding method. Everytime the beetle turns away after a short feed the equal distribution of food to a normal sized number of individuals is favored. Yet the instinct concerning this is rigid and she allows herself to be converted easily into useless activity by the experimentor, who reduced the number of larvae. Nevertheless, the female acts in completely the same way. Mittern feeding and again turning away following one another at typical rates at which then the beetle often enough holds her open mandibles in space, and just turns away in the moment in which one of the larvae approaches.
i. Ecology of Feeding.

Now the question is raised of what importance for the brood is feeding by the females. For the larvae, is it a matter of an activity necessary for living or of more secondary importance? This question can be decided very easily experimentally. If the female is removed before the first larval feeding, and if the larvae are completely dependent on the female, death of the entire brood must result. It appears that such a radical result does not happen. Most of the larvae grow up as if fed by the female.

The other hand points to two facts that the absence of the female in any case operates disadvantageously. Whilst in 8 rearings, which together included 89 larvae, under the care of females all individuals completed the 7 day development. From 147 orphaned larvae which were distributed over 14 nests, 16 animals in stages I & II died, so that in each rearing one dead larva was found on average. It is almost certain that the early death of particular larvae is connected with the absence of females, primarily pointing to the loss of food. Secondly it appears that without the female grown up larvae are able to pupate but very rarely do young beetles hatch from the pupae; from 33 such controlled pupae only one hatched. Under the unfavorable conditions of artificial rearing, the brood perishes in the pupal stage in roughly half of all cases even though fed by the female. The very much higher death rate of the brood raised without the female is certainly attributed to absence of parental care. Therefore it appears that the larvae are able to develop normally without the help of a parent animal, but that through feeding they are favored or protected.

Is what exists now an impairment from deficiency of food? Next comes the idea of something qualitative. The feeding female was able to supply the larvae some substance - if only a small quantity - which is important for development. This assumption was not refuted but it was unpredictable. It is assumed, that the deficiency of a specific substance in the course of development represents here completely expressed and believed to itself more serious aftermath if this is in fact the case in orphaned larvae; then still the larvae are able to complete their development to adult without the food of the female. Moreover it is not very probable, as p.570 showed, that the quality of food differs from that which the female has prepared in the area of the crater: presumably both show the same kind of mixture of carrion and gut secretion.

More likely the impairment is quantitative. Possibly the quantity of food which the female has already mixed through with gut secretion before the appearance of the larvae, does not suffice for the brood and must therefore be supplemented through feeding by the female. However, the feeding of the brood begins immediately after the appearance of the larvae when a deficiency cannot yet exist in the predigested food.

A second more distant possibility exists, why a sufficient quantity of food was missing for the larvae in the female's absence. The gravedigger used only small carrion as provisions of food for the brood. This specialization brings two-fold advantage: firstly, small carrion is more numerous than large: secondly. the beetles are only able to bury and work bodies of a small size.With these advantages however must be taken a distinct disadvantage: the rapid transiency of small carrion. The decaying process which proceeds from the surface towards the inside as oxidation events are tied to the equivalent of oxygen, in small carrion it leads in time to complete destruction, which would not be the case in large bodies. That only small carrion are used has been proved; this assumes that the development of larvae is highly accelerated. In fact the development time of Necrophorus larvae is strikingly short; a 7 day development with more than one year of each beetle larva subject to quality food material. Even the carrion and meat eating larvae of closely related Oecoploma thoracica took an average 34 days for their development (Heymons). This larva, unlike the Necrophorus larvae is not solely a carrion feeder, but can always breed on new food when freely moving around. Thus, the 7 day development period of Necrophorus larvae depends not perhaps on quality or quantity of food, but is fixed genotypically so that with or without the female, development takes 7 days.

The necessary and obligatory shortness of the available time to develop however requires complete exploitation. Just how are hatched or freshly moulted Necrophorus larvae unable to independently take up food because of the soft cuticle of their mouth parts. Through this condition repeated failure in the supply of food was effected, for the quantity of food which the larvae can take up in the time allowed in their condition, sinks below the optimum. It is as Fig. 22 shows, just the named development phase in which the brood is fed exclusively by the female. Therefore it is apparent that the female prevents through the feeding a break in the supply of food. The benefit lying therein is by no means insignificant. During the 60-72 hours feeding period the larvae are fed copiously by the female half the time. We see also that all appearances after the feeding instinct of the female serve the purpose, to secure for the larvae the necessary quantity of food for their development despite the--offered of other ground--shortness of their development time.

The short development time results in yet a further use for the species. The carrion which the grave digger must visit to feed to maturity and reproduce are distributed sparsely in distant parts. The problem of finding carrion becomes all the greater the longer time placed at the beetles disposal to visit the body; this time however becomes extended through an acceleration of development. Above all the short duration of development is of use for any species, such as N. vespillo or N. vespilloides which rears two generations in a year. The beetles of the second brood, which in N. vespillo hatch in the middle to the end of September, still find at this time favorable conditions to feed to maturity, which would become absent for them with later hatching, so that they would have to overwinter without feeding to maturity.

j. Defense of the larvae and their food.

Also in the period between feedings or after the conclusion of the entire feeding period one sees the nursing female sitting mostly over the crater (Fig. 23). Very conspicuous are the sudden movements with which the female turns here and there as the single entrance to the larvae might be protected by the towering female in all ways against possible enemies. However what are the enemies of Necrophorus larvae? Above all the male is mentioned. The male is already drawn attention to by Soffel (1904) as an occasional carrion eater. Although I was never able to catch him red-handed, no doubt the male ate up carrion and larvae in very many cases of my experimental nests. From an area of about 1 hectare he had expelled outright, after robbing in 3 days not less than 36 buried carcasses which had fallen victim, as was gathered from the existence and development of typical male tunnels.

Naturally what happens when this superior enemy comes face to face with a defense of the brood does not need to be questioned. This is still of value for the hostile insects which either as predators hunt after the Necrophorus larvae themselves or as carrion-eaters were able to impair the closely measured food for the brood.

One of the predators is the large Staphylinus olens Mull. It was found in 6 cases in experimental nests of N. vespilloides, among them 2 times in 2 examples. In all cases the nest, in which I had established a normal number of young larvae (I & II) only a few hours before, was found empty and with no trace of the larvae in the near surroundings. On the other hand in two of these cases elytra and legs lying around gave away the fact that females had also fallen victim to the superior enemy. Therefore the successful defense of the brood against this enemy in the event does not arise.

To the predators is further counted the Staphylinid Philonthus whose determination Herr. Prof. Dr. van Ender undertook in a loving way. Necrophorus eggs in the immediate vicinity of an N. vespillo nest in the soil were brought up together with the Necrophorus eggs but without the presence of Necrophorus females. They hatched out extremely lively Philonthus larvae clambered onto the ball of carrion, seized and consumed any Necrophorus larvae which had already arrived there. After 2-3 hours pause, in which the predator concealed itself in a hiding place, further attacks on N. larvae were observed. In 24 hours the whole N. brood was destroyed. A further look about by the visibly growing Philonthus larvae at this time failed as any suitable food was absent. Carrion and pieces of meat were scorned as were as older fly maggots. Suitable food, especially Necrophorus larvae, were unfortunately not at that moment at my disposal. Finally the restless, hunting Philonthus larvae died with wide open mandibles. However by this time the establishment of the species was frustrated so a possibility to determine the species of the larvae of the genus Philonthus did not exist at the time.

Philonthus eggs were found later several more times in the vicinity of freshly laid Necrophorus vespillo nests, in total 17 times. The danger to the Necrophorus brood through predatory Philonthus larvae cannot be totally averted through the vigilant female, but still substantially reduced. For in the wild I saw repeatedly, as the beetle succeeded now and again. she seized and killed the visible predator.


The female had further success in defending her brood against the hostile carrion-eaters than against predators. Additionally, one is justly allowed to mention all those insects which feed themselves or their descendants on carrion. From such were used the following species for experiment:


Necrophorus vespillo in 32 experiments

Necrophorus vespilloides in 32 experiments

Geotrupes sylvaticus 18

Oeceophoma thoracica 2

Silpha obscure 1

Lucilia caesar 1

In a weakly lit room a ball of carrion taken from a crypt, in whose insides were N. vespillo larvae of stage III together with the attendant female were put in the middle on the floor of an uncovered glass terrarium (52 x 40 x 27 cm) whose floor was covered up to a height of 1.5 cm with earth. The experimental arrangement allowed the hostile insect to be brought into the vicinity of the nest without the nursing female being disturbed through other than from the new arrival attraction.

All experimental results agree that a reaction of the female first becomes perceptible if the enemy was or even had climbed in the immediate vicinity of the ball of carrion. With their particular generic name the defending female made without exception the usual way with Necroporhus in the fight. From this same species were the dung beetles (G. sylvaticus) driven away, while Oeceophoma thoracica and Silpha obscura were driven away only several times in all cases and for this reason finally expelled. Only Lucilia caesar did not let itself be finally expelled. Although the Necrophorus female repeatedly rushed on the fly with quick movements, and frightened it away for moments, they always moved back again, till it finally succeeded in laying some eggs on the carrion ball. These were sometimes eaten later by the female as also fly maggots which developed in the ball of carrion are consumed by the female. How effective in fact must be the warding off of enemies of this species for in the Frankfurt woods are found almost on any free-lying carrion Geotrupes, Silphidae and often insects among them not rarely also feeding Necrophorus. As soon as digging Necrophorus are present, the remaining visitors disappear. So have I then, never during the whole time of my observations been able to discover any intruder within an intact crypt. This observation which covers also the very shallowly buried carrion of N. vespilloides, is all the more remarkable as Geotrupes was also found on the carrion, that I had covered several cm deep with earth and leaves.

 
k. Maintenance of the crypt.

The necessary opening of the crypt in the wild for observation led to the establishment of a remarkable regulatory instinct of the grave digger. The animal repairs the disturbed brood room. The following experimental descriptions serve to show the below surface observed activities.

A larval nest which belong to N. investigator becomes laid free through cautious removal of the crypt roof. The female which in the first moment was escaping, soon appears again, hurries round about the carrion, clambers up on it and tastes with the antennae the edge of the crater. Then it suddenly leaves the ball of carrion, climbs the crypt wall sidewaysand advances into the adjoining soil. Already the grave digger is half hidden in it, then she pauses and with stronger and from backwards directed movements of the hind legs hurls back loose earth. At the same time also the upper half of the beetle falls back into the lying soil. Then the female pauses, turns back to the crater and tastes alternately with the antennae the freshly raised material and the still partially uncovered crater. Then still once again begins the described spectacle at another place. Now is also plain to been seen, that the working animal through raising and lowering her thorax shakes the earth mass lying over her and through that, brings it sliding off. Soon the ball of carrion is completely covered with earth. The female ceases working and disappears under the spilled material. Once more opening the brood hole at the end of 4 hours shows that the crypt is again completely made: the ball of carrion lies in a cavity with smooth walls as before the disturbance.

The typically expedient behaviour of the grave diggers remains throughout in the frame of demands which in the wild are put on the animal. That the Necrophorus sank carrion only a few cm in the earth, may have occurred frequently enough that from the natural reasons, perhaps through the step of a grazing animal or a heavy downpour, the crypt fell together and the brood often lay there abandoned from damaging weather and hostile persecution.

It is unknown which kind of attraction caused the repair instinct. Three different kinds of attraction which singly or in combination were able to work, lie in the realm of possibility.

1. With the disturbance of the crypt often a sudden lighting of an entirely dark brood room occurs, consequently the possible attraction to an attractive light exists.

2.The stagnant air in the crypt over-ladened with waste products, for example CO2 and H2O, would essentially entirely change through the inflow of fresh outside air. The causal attraction would in this instance be primarily chemical.

3. A crypt can be sunk without connection with the outside world, thus offering another kind of attraction. As a result of the original kind of crypt the nursing female fits in the space between the ball of carrion and surrounding earth, touching the crypt wall only lightly with the back. By collapse of the hole, the light on the back of the beetle either suddenly intensifies or is completely lost. Any intensive change of this kind is able to be the cause of attraction.

Occasional support that, for the mentioned attractions of contact for the activation of the repairing instinct are of decisive meaning. A final difference however falls requires thorough experiments which ought to be made in the coming summer.

1. Defense of males at the nursing.

Although the males in the majority of cases were no longer found together with the larvae in the nest (Table 5), N. vespilloides and N. germanicus were observed feeding, and presumably males of the remaining species do so as well. The fact that male grave diggers are also equipped with a broodcare instinct, is not surprising as the participation of the male in the broodcare in beetles is a known occurrence. One is reminded of the group of coprophagous lamellicomier amongst whose representative are found numerous genera with highly differentiated broodcare in which the male of many species participates. I]hy, inspite of the qualification of male grave diggers for broodcare, was contribution of the male only observed in exceptional cases. Two explanations are possible:

1. The male was able after fulfillment of his task, which on the one hand in the capacity of working to bury the body, on the other making the female to fly away in search of another carcass and through renewed ingression of task be useful at another place.

2. Certain signs suggest that broodcare instinct of the male is less pronounced than that of the females. It is conspicuous that feeding male offers his food juices to the brood at greater intervals than the nursing female. While the young beetles groomed themselves often and leaning of the nursing grave diggers was confined to the cleaning of eggs and antennae. When the larvae leave the nest, one sees the female respectively the pair completely dirty (Fig. 23) and often with mites sitting dotted in the rest of the body. Without feeding or cleaning the parent animals spend for 2-3 hours of the carrion, till they finally remove themselves from the crypt and return no longer.

 
m. Development of full grown larvae to young beetles.

Shortly before the conclusion of the 7 day period of development the brood ceases to take up food. Up to this point the near white looking larvae are colored yellowish and at the same time become broader and flatter. The animal, which at this stage can also be described as "prepupal", shows a different behavior from the larvae III stage. The continuous massing together of the larvae under one another ceases. The animals bore through the outer layer of the ball of carrion and advance singly into the soil to pupate. Fig. 25 illustrates an abandonded carrion which remains behind hollowed out and with a hole through it. Over the depth as far as to the dug in Necrophorus-larvae, Xambeu (1892) Chenn and Desinarest (1851) have already made statements. According to Xambeu (1892) the N. fossor pupae are found in 15 cm depth, from Chenn and Desinarest N. humator in 60 cm. My results differ from the named works: the depth, up to which the larvae were able to advance to pupate is dependent naturally on the respective depths of the crypt. From the brood cavity the pupae move predominantly in the horizontal plane up to 30 cm from the nest and in doing so only bore themselves a little deeper. So one finds for example the pupae of N. vespilloides 1-5 cm under the earth surface, however in a particular case directly under the most respectively raw humus layer. But also for the deeper digging species N. humator the estimated values of Chenn and Desinarest are, at least for the individuals living in the surroundings of Frankfurt, regarded as clearly too high. At the end of their wanderings the prepupal stage pauses to build the pupal cradle which originates through long hours of rotation of the larva on its long axis, as already shown by Fabre.

Four of the mentioned Necrophorus species, namely N. germanicus, N. humator, N. vespillo and N. vespilloides pupate after a pause for rest of 12-17 days and complete their development still in the same years. N. fossor and N. investigator are different. There the newly emerged adults _ of these species appear in the surroundings of Frankfurt all at the end of June at the earliest, so the young generation also run through the larva and development mostly first in September. After that the animal enters a standstill in development: the prepupal stage overwinters in the pupal cradle. Xambeu (1892) had already stated this for N. fossor and Main (1927) also noticed that at least one species overwinters as a larva. That the break in development is not a direct result of environmental factors for example low temperature, but view as fixed genotypical development rhythm, is shown in the following experiment. The wandering larvae of both these species were put at the beginning of October 1930 in their rearing cage in a greenhouse in which the temperature of 19_C , prevaded. Although under the same experimental conditions other ~ Necrophorus species had already developed up to the pupa, the larvae of N. fossor and N. investigator remained standing at the pre-pupal stage and died off gradually during the winter. Control animals taken from the same nest put in the smallest_flower pots, filled with earth, shut above with wire gauze, buried a ~ w cm deep in the Botanical Gardens of the University of Frankfurt and the~_oil-there covered with a layer of leaves. In April of the following year (1931) these animals were found in strong health in the prepupal stage, pupated at the end of May and emerged at the conclusion of the pupal rest to adult.


The pupal rest of the grave digger lasts 14-15 days. The pupa rests only on the strongest bristles which are found on the eyes and the pseudocerci and the ventral side turned downwards, in the small subterranean cavity. At the irritation of touching the abdomen the bristles beat or make circular movements. Two days before the hatching of the young beetles, the initially white pupa becomes brownish. The young beetle which frees itself from the pupal covering, already has gold/brown extremities and a likewise colored thorax and scutellum. The elytra, are white/yellowish, are only indistinctly marked. Under normal conditions, the animal remains in the protection of his subterranean room. until 4 days after the casting of the pupal skin when the complete coloring and hardening of the chitinous skeleton occurs. First then the young beetle breaks through the wall of his pupal cradle and works his way through to the surface of the earth. The light color and the silk smoothness of this armor betrays the young beetle, which goes off without delay in search of food. After a maturing feed, which is completed in 10-14 days in N. vespillo and N. vespilloides, the young beetle is ready to reproduce and qualified for the combined performance.

SUMMARY

The investigation extended to the species: Necrophorus germanicus, L., N. humator, A., N. vespillo L., N. vespilloides Herbst, N. fossor Er., N.investigator Zett.

1. N. vespillo is native in meadows. N. humator and N. vespilloides are confined to wood areas. N. humator is found predominantly in humid deciduous woods, N. vespilloides in dry coniferous woods.

2. All species feed themselves on carrion and diptera larvae; N germanicus also eats Geotrupes.

3. Extra intestinal digestion of the adult is probable.

4. Before the burial every carcass is examined for chemical condition, size and ease with which it can be shifted.

5. Sexually mature males, which find themselves alone at the burial of a suitable body' attract the female of their species through "Ventilation".

6. The isolation of a single pair from a large number of commonly burying individuals is based not on social instinct (Fabre 1988, Reuter 1913, Schroder 1929) but on fighting.

7.The burying does not advance alone through digging under the body. This is rather conveyed in the course of the digging activity in a slanting hole leading into the depths at whose base lies the ball shaped brood chamber (crypt - Fabre 1~899).

8. Simultaneously with the construction of the crypt, the rounding and cleaning of the buried body advances.

9. The eggs are laid singly on both sides of a horizontal outgoing passage from the crypt into the soil, the mothering passage.

10. In the majority of cases the males which shared broodcare with the female are driven away out of the crypt after completion of egg-laying.

11. After egg-laying the ball of carrion is damped with excrement from the female and on its upper pole mixed through with gut secretions.

12. At this point, which is deepened by the female into a circular crater shortly before the appearance of the descendants, gather the hatched larvae at the end of 5 days embryonic development, which distinguish themselves in the first stage through good ability to smell.

13. The larvae go through two moults and are fully grown in 7
days.

14. A female is regularly found by the brood in the crypt, rarely a pair. The grave digger practices highly developed broodcare:

a) The brood is fed by the female with gut contents. The time of feeding extends over the first 60-72 hrs. of larval development.

b) The brood is defended against enemies.

c) The crypt is repaired after destruction.

Males which are not expelled by the female, participate in broodcare.

15. At the end of a 7 day period of development the larvae leave the carrion and predominantly withdraw from the brood room in a horizontal plane.

16. The species N. germanicus, N. humator, N. vespillo and N . vespilloides overwinter as adults, N. fossor and N. investigator in the prepual stage.

17. The pupal stage lasts 14-15 days.



......... transcript ends.

Please use your browser 'Back' button to return to previous page.