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"A Nature Observer′s Scrapbook"

Galls Page 1
- galls found on trees and shrubs.

Dog Rose galls

So what is a gall? A general definition states that :-

"A gall is an abnormal growth produced by a plant or other host under the influence of another parasitic organism. It involves enlargement and/or proliferation of the host cells and provides both shelter and food or nutrients for the invading organism. The association between the causal agent and the host is usually quite specific."

....... which means that specific causers are very selective about the plant species they associate with.

The scientific name given to a gall very often reflects the name of the causer - whether that be bacteria, fungus, nematode, insect or mite.

Most galls forming on plant stems take on a hard woody form, the oak apple being a well known example.

Robins Pincushion Robins Pincushion

Robin's Pincushion or
.... the Bedeguar gall

Diplolepis rosae

This is a spectacular gall and quite commonly seen on Dog Rose hedging. Colouration can vary from green to brilliant scarlet and eventually degenerates to rusty brown. Even small, newly formed galls can be scarlet, and some old mature galls can remain green, so colouration would not appear to be linked to maturity. Perhaps the colouration is down to what part of the plant, or which cells, have been invaded.

Eventually, as autumn approaches and the host plant starts to die back, all the galls take on a rusty brown colour and those having developed on the stems and branches will remain very much in evidence (hedge trimming permitting) even after leaf fall - as evidenced by the lower image which was taken in March.

The 'causer' in this case is a gall wasp (Diplolepis rosae) which lays its eggs in either the leaves or stem of the dog rose. One gall may contain several grubs, each in an individual chamber.

Subsequently, other insects may invade the gall. Some may be innocent tenants (inquilines) simply taking advantage of the gall and subsequently causing enlargement of the structure. But, others may be be parasites of these inhabitants and others may be hyperparasites preying on the parasites. It has been estimated that as many as 14 different species may be found within Diplolepis rosae galls. All the gall grubs will overwinter inside the 'apparently' dead gall, to emerge next Spring.

15.06.2003All Hay Meadow hedgerows.
21.06.2004Present in PRV and haymeadow hedges but not as many as last year.
10.09.2004A late flurry of new sightings. How many will mature before hedge cutting is another matter.
20.03.2005An overwintered survivor found by Benniworth car park. No sign of exit holes.
04.04.20058 rusty brown galls with no exit holes found on dogrose in the Protected Roadside Verge at TF 3105 6598.
26.08.2005One solitary group of five galls clustered on one wild rose stem, east side of hay meadow..

Dog Rose Pea Gall Dog Rose Sputnik Pea Gall

Dog Rose Pea Gall

Diplolepis nervosa

This Pea gall comes in two forms. There is the smooth spherical form and the spiky 'sputnik' form. If shaded from the sun both forms will tend to remain pale but exposed galls will ripen to a colourful pink.

The smooth galls appear mainly on the leaf's smooth upper surface. The spiky galls, on the other hand, appear to predominate on the underside of the leaf close to veins where small thorns are found, or at leaf edges where sharp leaf serrations occur. I cannot recall ever seeing a spiky gall on the smooth upper surface of a leaf.

But, that observation is specific to this species and cannot be used as a generalisation. A Canadian viewer has advised me of a North American dog rose pea gall, with very long, dramatic, scarlet spikes - almost certainly caused by a different insect, which develops on the smooth upper surface of the leaf!

Each gall is, in effect, a hollow, fleshy nursery chamber for a small white grub, the larva of the Diplolepis nervosa gall wasp, which feeds on the chamber wall. The galls appear to detach from the leaves before leaf fall and will lie in the leaf litter until the grub pupates and emerges as the small adult wasp, only about 4mm long.

I suspect that there may be more than one generation a year.

03.08.2003All Hay Meadow hedges.
20.07.2004First galls seen but not nearly as common as in 2003. All were spiked galls and on the underside of leaves.
03.09.2004A late, but small, flurry of new sightings - all smooth. One pair, at 8mm diam, were the biggest I have seen.
August 2005New galls are very few and far between this year - and no spiky ones.
14.07.2006First group of new galls seen in eastern hedge of meadow - and most were spiky.
13.08.2008First groups of new galls seen in E and SW hedges of meadow - and most were smooth!

Folded leaf rose gall folded leaf rose gall larvae

'Folded leaf' rose gall

Wachtliella rosarum or
..... Cecidomyia rosarum or
.......Dasineura rosarum

This gall is found on various species of rose and the characteristic tight folding of the rose leaflets is easily spotted. It is widespread and common throughout the UK.

As the gall develops, the swelling along the mid rib becomes discoloured making the gall even more noticeable.

Most folded leaf 'deformities' are held together with silk or some other adhesive device but in this case the internal leaf structure is changed to hinge the leaf surfaces together forming a tight closure that can be difficult to separate.

Within the fold can be found several small larvae upto 2mm long. In their early stages they will be creamy white, as seen in the lower image, but as they develop they go through a yellow, orange, red colour change prior to pupating.

The emergent adult is a midge of the large Cecidomyiidae family, known as Dasineura rosaria.

15.08.2008 Larve found in the disorted leaves of Dog Rose growing through a mixed Hawthorn hedge.

Phragmidium Spp Phragmidium Spp

Orange Rose rust

Phragmidium tuberculatum - or

Phragmidium mucronatum

Galls can be induced in plants by bacteria, fungi, other plants, nematodes and, most commonly, insects. As the common name of this one implies, this is a fungal induced gall.

Very little definitive information has been gathered regarding rusts on roses. Only detailed microscopic examination of the rust spores can differentiate between the specific causal agents and in the absence of that, the safest identification would be Phragmidium spp.

As can be seen, as the gall ages it becomes progressively darker and eventually becomes sooty black in appearance.

03.08.2003Hay Meadow, eastern hedge.
04.06.2004Two instances seen close together in Hay meadow hedge, SW corner.

Diastrophus rubi Diastrophus rubi

Bramble stem gall

Diastrophus rubi

The Bramble stem gall is characterised by a longitudinal hard swelling of the stem, roughly the thickness of ones little finger, say 10 to 15mm in diameter. They can vary in length from 2 to 15 cms.

The upper image shows a gall prior to the emergence of the adult gall wasps but because old galls can remain on the stem for several years, one is more likely to come across old galls riddled with the exit holes, similar to wood worm, of earlier years emergent adults (lower image).

A large gall could contain as many as 200 grub like larvae. The causer is the small black gall wasp Hymenoptera: Cynipidae: Diastrophus rubi.

In 2008 a large group of 34 new galls was found within the space of 5 metres on the spindly stems of three leaved bramble thought to be of the Rubus caesius agg group. This was an exceptional find in my experience, having previously only seen these galls as sparcely separated individuals.

diastrophus rubi wasp

Being confronted with such a large number of galls, I felt it 'reasonable' to harvest one early in 2009 and in April 2009 I was able to see some 40 plus tiny gall wasps emerge. Being only 2mm long I am sure that I would not have recognised them as wasps had I not seen them emerge. Initially they were covered in a fine pale creamy 'dust' from the residue of their individual gall chambers and that required significant grooming to wipe off.

It is only with the benefit of photographic enlargement that the characteristic 'wasp waisted' body feature and the wing venation can be seen.

December 2003Hay Meadow, western hedge.
April 2004Hay Meadow, eastern hedge.
04.04.2005One unhatched gall and 19 old galls found in a 8m stretch of the Protected Roadside Verge hedge at TF 3105 6598.
29.08.2005 One new example seen on eastern side of hay meadow.
08.08.2007 One new example seen on eastern side of hay meadow.
04.08.2008 Three old and 34(!) new galls found in low growing brambles on ditch bank.
05.04.2009 In excess of 40 tiny wasps were seen to emerge from a smallish gall.

The ash tree gall

Ash key gall

Aceria fraxinivorus

This proves that one never sees what is right under one's nose - or just above one's head. I could not recall ever seeing this before, but once found, it appears to be very common and very prolific. I have been sweeping Ash keys off the patio for years and never noticed any of these galls before. Perhaps because they are heavier and less aerodynamic, they do not get wind blown as far as the keys, and may fall closer to the base of the tree.

....... Or is it all down to 'mast year' theory? It is well documented that several tree species go through cycles of prolific years of seed production ('mast years') followed by barren years.

Many of the Ash key galls produced in 2003 remained on the trees throughout 2004 - when, so far as I could see, no seeds, or new galls were produced at all.
2005 saw seeds being produced again but no galls.
And 2006 saw good crop of seeds being produced and a return of the galls.

So, (he proposes), might it be that a massive gall infestation one year, which leaves galls (and their causers) on the tree the following year, inhibits the seed production of that year. With no seed production to infect, the gall causer population - tiny 1mm long mites (Acari: Eriophyoieda: Aceria fraxinivorus) will plunge, and will take a few years to recover?

Well, ...... it's a theory.

The galls form very hard woody encrustations on the seed bearing stem.

08.10.2003Ash trees in the locality have seeded well and many are carrying galls.
2004No Ash seeds produced at all, therefore no new galls.
2005Some Ash seed clusters produced but not a gall in sight.
August 2006Many Ash seed clusters produced and several are bearing galls.

Underside of leaf Upper leaf surface

Ash leaf gall

Dasineura fraxini

This is a very common gall affecting Ash tree leaves. It is caused by a tiny fly (Diptera: Cecidomyiidae: Dasineura fraxini) and characteristically affects the underside of the main vein of the Ash leaflet (upper image).

Each swelling is occupied by one small larva which after its transformation into a fly, eventually 'escapes' through a small slit on the upper surface (lower image).

In severe infestations it is not unusual to see several such galls on one leaflet and they can also be found on the petiole (leaf stalk).

08.10.2003Severe infestation on many local Ash trees.
2004As with the Ash Key galls, none of these were seen in 2004 either!
30.08.2005A few examples spotted on the Ash in NW corner of Burton's Paddock.

Kilmarnock willow gall Pontania bridgmanii gall wasp larva

Salix caprea gall

Pontania bridgmanii

I had originally named this gall Pontania gallarum, but after cross referencing this with other ID factors I am now convinced that it is really P. bridgmanii.

These galls are very common on the Kilmarnock willow (S. caprea pendula) in our garden. Although the galls themselves can be relatively inconspicuous, the saw fly caterpillar larvae tend to eat the leaf directly in front of the exit hole (as seen in the lower image), presumably so that they can beat a hasty retreat if danger threatens. So, inspection of damaged leaves quickly highlights the galls.

The gall chamber is domed above and below the leaf and, taking after the structure of the leaf, is smooth on top and pubescent below.

10.09.2003On Kilmarnock willow, back garden.
20.05.2004Galls already forming but no signs of larvae emerging.
31.05.2004What was thought to be an adult gall wasp, apparently ovipositing on a leaf which subsequently sported three galls.
21.04.2005An earlier sighting of the adult gall wasp. Leaves on the Salix have only just broken out of bud.
30.05.2005First galls of the season spotted - but they look quite large and could have been there several days.
06.07.2005Much evidence of larvae feeding - and one spotted in the act.
28.05.2006First gall of the year seen.
12.05.2007First gall of the year seen - but subsequently not many, until .....
16.08.2007..... Many galls found. Some five to a leaf, whereas in the past they have been solitary or two to a leaf.
10.05.2010 First galls of the year seen .

P. gallarum, top view P. gallarum, side view P. gallarum, bottom view

Salix caprea gall 2

Pontania gallarum

After my initial indecision with the previous species, this is much more likely to be the classic P gallarum.

It does not appear to be as prolific as P. bergmanii. The gall is close to the central leaf rib and has a distinctive depressed 'scar' on the upper surface.

The appearance of the gall on the lower surface is oval in plan view and symmetrically rounded as seen from the side. And the pubescence on the underside of the leaf appears to be accentuated on the gall wall.

The overall length of this gall was 7.5mm when found and did not seem to materially increase with time.

There is still a fair degree of uncertainty about the key identification features of these galls and the rearing of mature insects is recommended for positive identification. That, however, would still require microscopic examination and some significant expertise.

03.07.2005 Found on the garden Salix caprea pendula.
09.09.2005 Despite monitoring this gall regularly, the entire leaf has disappeared! No sign of it in the litter beneath. Mystery.
28.05.2006First gall of the year seen.
12.05.2007First gall of the year seen.

Field Maple gall

Field Maple gall

Aceria macrochelus

The galls, 2-4mm in diameter, are prominent on the upper side of the leaf, invariably occuring on a leaf vein or at the junction of leaf veins.

Caused by mites, the galls form hard walled pouches, some on elongated stems, with minutely hairy openings on the underside of the leaf.

28.08.2004Field Maple on the Southern side of the Banovallum House car park quite heavily 'infested'.
19.08.2005Same Banovallum House Field Maple not so 'infested' this year.

Oak Spangle gall Oak Spangle gall

Oak Common Spangle gall

Neuroterus quercusbaccarum

This very common gall is caused by a gall wasp, (Hymenoptera: Cynipidae: Neuroterus quercusbaccarum).

Each gall is 'discus' shaped and attached to the underside of the leaf by a short stalk. The surface is minutely bristly.

The galls remain on the leaf after leaf fall and overwinter in the leaf litter. Female only wasps, barely 3mm long, emerge in Spring and lay eggs in the male catkins. These give rise to currant-like galls in June whose larvae will develop into both male and female insects.

It is the female of this generation which will lay her eggs on the underside of the leaves to cause the Common Spangle gall.

Several different spangle type galls are to be found on oak leaves so close inspection is required for proper identification.

30.10.2004Heavy infestation on young oaks in Carmen Wood, Benniworth.

Oak hop gall

Oak hop gall
..... or artichoke gall

Andricus fecundator

This is another common gall on oaks. A young gall will exhibit a tuft of long hairs protruding from the centre. These are attached to a solid gall which is expelled from August onwards. So this image is really of the distorted leaf bud after the gall has fallen.

The gall wasp which emerges from the gall chamber in Spring will always be an asexual female. But she will proceed to lay eggs on oak catkins which develop into 'hairy catkin galls'. The wasps emerging from these galls will be of both sexes and after mating, these females will go on to lay a solitary egg in leaf buds which will cause the formation of the 'hop' or 'artichoke' galls.

20.03.2005 Found on young oaks in Benniworth 'nature reserve' area.

Oak Marble gall

Oak Marble gall

Andricus kollari

As a youngster, I always referred to these galls as 'oak apples' - but then, I had never seen a proper 'oak apple' (Biorhiza pallida) which can be up to two inches in diameter. At up to 20mm diameter, these more appropriately named oak marbles, are very common, if for no other reason than that the old galls can remain on the tree for several years.

New galls found on oaks in the spring can be bright green but quickly become brown and very hard.

Each gall normally houses one larva of the gall wasp, Andricus kollari - and possibly, several inquiline (foreign squatter species) intruders. When mature they vacate the hard woody sphere through tiny holes similar to 'woodworm' holes.

28.08.2005 On young oaks by the Benniworth caravan area car park.

Oak Cherry gall

Oak Cherry gall

Cynips quercusfolii

Whereas the Oak Marble gall, which grows on stems and buds, is of similar size (20mm diam.) and appearance, this gall is to be found on the underside of a leaf. It is normally solitary but occasionally a small group may be found together.

Taking after the leaf cell structure, this gall is more succulent than the Oak Marble and depending on the species of Oak, may be smooth or slightly warty.

The gall develops from yellowy green through dark red (cherry-like) to brown.

The grub may remain within the gall after leaf fall to emerge as the gall wasp Cynips quercusfolii in mid-winter. This asexual generation will lay eggs on or close to the Oak trunk in spring which will give rise to tiny purple sexual generation galls close to the tree trunk. On maturing, the sexes will mate and in turn produce the larger and more visable Cherry galls.

03.09.2006 Found in the Benniworth conservation area.

Acorn cup gall

Acorn cup gall

Andricus grossulariae

There are two versions of this gall caused by the small gall wasp Andricus grossulariae. In Spring, galls forming on Oak catkins will contain bisexual grubs. These galls only grow to about 6mm and appear shaped like pointed peas.

In late summer and autumn, the galls found on the acorn cups (such as portrayed here) will contain asexual grubs and are much larger and more contorted in shape.

In both cases the galls first appear pink in colour and as they mature they turn red, then green and finally brown.

In most cases the late galls confine themselves to the cup of the acorn. But, in some cases the gall may grow vigorously over the acorn thus trapping it within the cup. It can then be confused with the acorn Knopper gall, Andricus quercuscalicis (see below), which invades both the acorn and the cup.

22.10.2006 Found in the conservation area at Benniworth.

Acorn Knopper gall

Acorn Knopper gall

Andricus quercuscalicis

The gall wasp Andricus quercuscalicis is responsible for this gall which forms on the actual acorn.

The growth appears as a mass of ridged plant tissue. If only a few grubs are developing within, it may present as a group of bland folds. Where several grubs are competing for space the shape may become much more contorted.

When the growth is vigorous the gall can completely enclose the acorn and hide it from view.

This gall also develops through red, green and brown stages.

03.09.2006 Found in the Benniworth conservation area.

Yew gall, Taxomyia taxi Yew gall, Taxomyia taxi, withered example

Yew bud gall

Taxomyia taxi

There are only two galls that affect Yew buds and this particular one comes in two forms. It can either mature in its first year with a cone shaped structure only about 6mm tall or, it will remain in growth into its second year with a more substantial cone between 1 and 3cm tall. This is the more common form. The upper image is of a 2cm cone found in April which would be expected to mature in July.

It is caused by the tiny orange coloured larva of the Yew gall midge (also called Taxomyia taxi). The larva will eventually pupate and the adult midge will fly in July.

By this time the gall will begin to die back, the individual leaves becoming limp and bronze and relaxing from the tightly formed cone shape. In this state, from a distance, the galls could be mistaken for a show of flowers against the dark green healthy foliage.

And, as seen in the lower image, tufts of dead brown leaves can persist on the stem tips for some time before autumn and winter winds shake them off.

18.04.2010 Found on Yews bordering Revesby reservoir and in the grounds of the Horncastle Medical Group practice.

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