When I saw plant galls for the first time I wanted to know what species there were to be found basically, and so I started collecting anything that looked like a plant gall. Boxes full of them I have now. Nowadays I think it is better for me to take pictures (digital or slides) and when you are interested in the gall maker itself, it is a good idea to try to get the inhabitants to emerge from the galls. The list of species described below are gall makers and their hosts, from species that I myself or another gall studying person has seen. A description is given and, where possible, a picture. For people who are interested in the Dutch distribution of pant galls can soon take a look at the database we are preparing for this website. Since the subject of plant galls becomes more popular only recently, we do not have yet such an extended database. Any contribution is welcome!

Andricus ariesLast 24th of May 2003 Jan Willem Wertwijn, discovered a couple of specimens of Andricus aries in park Spoorzicht at Diemen (km-hok 126x484). This gall wasp was, until now, unknown for the Netherlands and are therefore not described in Docters van Leeuwen. The gall has no Dutch name yet. The galls show some likeness with the horns of a Ram and because the English also use the name Rams Horn Gall, it seemed a good idea to Jan Willem Wertwijn to name the gall ‘Ramshoorngal’. The Rams Horn Gall was, until 1998, not seen before in Central-West Europe. In 1998 the first English specimen were discovered in London (Cecidology 14 (1): p.18–21, C. K. Leach & P. Shirley) and since then the species has been located at different areas in and around London. In Germany the gall was discovered more early by Eckbert Kwast in 1990 on Quercus robur in Spremberg in the Southern part of Brandenburg. The species is also found at three sites in the near Saxony (Cecidology 16 (2) p.62–68, E. Kwast). The species is common in Hongary.

There is not much know on the live cycle of A. aries. The species was found on Quercus robur, Q. petraea and Q. pubescens. It is possible that the species needs Quercus cerris for the sexual generation. This oak is also spreading, due to planting of trees and this could explain the current distribution of the species. The gall is being described (Cecidology 15 (2) p.131–134, B. Wurzell) as a gall consisting of a swollen and more or less roundshaped base, ending in one or two grooved, twisted, horn-like shapes between 0,5 and 4,5 cm long. The galls contain two to five hard cells, each with a larvae on the bottom and usually an empty pyramid-shaped or chimney-like hollow space on top. The galls are grey brown to black and are connected tightly to the branches. Empty specimen only have one exit hole. These galls are all hard and woody. The description of the galls is from a find in January. The description by Ross (1911): “horn shaped galls that contain only one gall chamber, 5-8 mm long and 4-6 mm wide with a long, to 50 mm, hollow (narrowed) ’neck’ on Quercus robur. The adults emerge during August and September.” This last part is still the case. A number of the galls found by Wertwijn had early September not yet hatched.

The picture at the botom show several exits: inquilines or other parasites?

Pictures: J.W. Wertwijn

gal met meerdere uitsluipgaten.
Foto: M. Bos

Andricus corruptrix The gall on the picture is the agamic generation in the buds. The sexual generation induces galls in the buds of Turkey oak,Quercus cerris.
Picture: A. de Vette

Andricus curvator can be found on the leaves of Quercus robur sticking out on both sides a little. The gall is green and bold and a little hairy at the bottom. The edge of the leaf is deformed at the spot where the gall is situated and is pulled inside in the direction of the main vein.According to Docters van Leeuwen (1982) the galls are often clustered together.

Andricus foecundatrix (or 'artichoke gall' or 'larch-cone gall') causes the agamic generation onQuercus robur. The gall is very common and looks most like a female Hop-flower. The scales have a v-shape under the edges.The gall is formed from June to September and mature in July. The wasps emerge in Spring, 1 to 3 years after forming the gall. They pupate in the gall on the ground.The wasp is positioned in the middle of the globule in a cone that is shot from the gall around August. After this has happened, the galls start to look a little messy and dried out.

The wasps of the sexual generation were known asAndricus pilosus, but since it is the same species as the agamic generation we can also call itAndricus foecundatrix. I have no image of this gall. They are up to 2 mm, rounded and pointed, covered with long white hairs. You can find them between the male catkins of oak in May, first green an later brown. The wasps emerge from late May untill August in the first year (Williams 2005).

Picture: E. Jacobs

Picture: T.J.M. Janson

Picture: A. de Vette

On Quercus lusitanica

Andricus glandulae of Klokgalwesp komt voor in de knoppen van zomer- en wintereik. De foto is de agame generatie. De sexuele generatie veroorzaakt meeldraaggallen. 

Andricus inflator - The galls caused byAndricus inflatorcan be found onQuercus roburon the ends of its young branches. With the agamic generation the swellings at the apex produce a shortened and thickened twig (top picture). The buds and leaves remain near on the gall. Inside there is another gall of a few mm in size where a larva can be found at the base. The sexual generation induces a gall in the buds (picture below).

Picture: R.J.Koops

Picture: H. Holsteijn

Andricus kollariis a wasp that induces hard marble galls onQuercus robur. They have a round shape and a smooth surface The gall is commonly known and is also often in use by other (hyper)parasites. Once I had this marble gall lying on a bookcase and suddenly little flying creatures started to appear. The holes they created were slightly smaller and the species appeared to beSynergus umbraculus, also a wasp. 

Picture: R.J. Koops

Andricus lignicolus makes galls on Quercus robur that look a lot like Andricus kollari, exept they are only 1 cm in size. They are really common. Contrary to A. kollari,  A. lignicolus has a surface that is quite rough and cracked.  The gall chamber is located more to the base of the gall instead of the centre.

Andricusparadoxus on buds of Quercus robur.

Andricus quercusradicis I found on twigs and main veins of leaves of Quercus robur in Wehe- den hoorn, in the north of Groningen. The veins and twigs are slightly thickened and easy to recognize because of the holes the wasps create when the emerge.
The asexual generation causes the huge swellings on the base of the trunk or on the roots. These galls can grow to be about 8 cm. The gall on the photo is also something like 7 cm.

Picture's: H. Pras

Andricus quercuscalicisinduces galls at the borderline of acorn and cup ofQuercus robur orpetraea. The gall is about two centimeters and very irregular. The cone-shaped globes are strongly folded and sticky. Together with the acorns they fall from the tree, which makes it easy to collect them. I spotted my first in 1997 in Wisley Gardens, UK, and this spring 2002 a friend showed me were to find them at a spot in Oosterwolde, Friesland. Those were my first findings of this species in the Netherlands! Near the Quercus robur trees were also manyQuercus cerris, which are necessary for the sexual generation.

Andricusquercustozae On oak trees in Southern Europe are many, very different species of Andricus, likeAndricusquercustozae.The gal is the asexual part of the wasps lifecicle. Friends and familie bring them from the noth of Spain and Greece (see pictures). This gall looks a lot like the marble gall (A. kollari), but is much larger, 20 to 40 mm, and it has a pointy dot in the middle on top and a crown of these elevations encircling this centre. The gall occurs onQuercus robur,Q. sessilifloraQ. pubescensQ. pyrenaica, etc. The species is not mentioned in Docters van Leeuwen, but you can find it in Meyer, Buhr en Dauphin & Aniotsbehere (seeliterature). The galls can remain on the tree long after the wasps have left and the gall can become inhabited by many kinds of organisms.

Pictures: L. Deiling en H. Boon

Andricus solitariusinduces little bottles onQuercus robur. First, I only saw the gall in autumn, when they are bold and smooth and every bottle has little hole were the wasp came out. In 2001 I came across galls with brown hairs. The gall really looks like a bottle with the top slightly bent and its size is a bit more than a half of a centimeter.

Andricus testaceipescauses galls on the stem or trunk of Common Oak that look like barnacles, hence the name barnacle gall. The galls are conical and often pointed and 4 to 6 mm high and 4 to 5 mm wide. On the pictures old galls can be seen with only the cores showing still. The gall is first red and soft and is ridged. The exit hole is situated on the side. The stem can be swollen. In DvL the species is still calledAndricus sieboldi.

Picture: H. Pras

Aphelonyx cerricola causes serious swelling around twigs of Turkey oak,Quercus cerris. The galls are green when young and later brown and hard and about 1 to 2,5 cm. The gall has one gall chamber and an internal airspace, when mature. According to Redfern et al. (p. 401) several galls can coalesce. According to Buhr (nr 5549) the galls are 1,5 cm. Buhr says the galls are covered with felt hairs when young, the galls have a thick outer shell and are dry and hard, usually growing on thin twigs, inside with usually one (rarely two) ovalround inner gall. 
This species is interesting because it only causes galls on Q. cerris and the galls are agamic (only females). Most galls on Q. cerris have a agamic generation on Quercus robur and a sexual genereation on Q. cerris. A sexual generation of Aphelonyx cerricola is not known. The gall in this picture was found in Rotterdam.

Picture: G. Menting

Aulacidea hieracii is a wasp that causes large swellings in the top parts of different species of hawkweed (Hieracium). An uncle and aunt found the specimen on the top picture on the isle of Vlieland one Autumn. The galls are supposed to be a little bit hairy. the gall is green at first and brown and bold later. The galls can become up to 5 cm by 2 cm in size. The plant parts above the gall can be reasonably well develloped.When a gall grows cclose to a flowerhead, the latter can become distorted. The gall hosts several round gall chambers, accomodating the white wasp larvae.

The bottom pictures were made again on the isle of Vlieland, and were this time found by Roelof Jan Koops. From the galls crept many wasps in early summertime. We have to keys those to a specific name sometime. At first sight they appear dark and small: Aulacidea hieracii? Ha ha!

found by L. and W. Neijzen

Pictures: R.J. Koops

Biorhiza pallidamakes use ofQuercus roburon the roots or on the branches. I have not yet seen the galls on roots, but you can find them anywhere on branches.  The galls develop into beautiful, spongy, irregular round globes. They can become three centimeters in size and the colors are very nice. Green, white, yellow, reddish and a little violet.

Picture: T.J.M. Janson

Cynips divisacauses red shining marbles to appear on the underside and sometimes upper side of the leaves of Quercus robur. One is more round than the other and they are all a little flattened. the galls are not any bigger than a half centimeter. The red color when they are fresh makes them worth looking at. Later the galls will turn brown. The walls of the galls are thick and surround a small chamber. The galls fall down with the leaves.

Picture: J.W. Wertwijn

Cynips longiventris The agamic generation causes neat rounded galls on the underside of the leaves ofQuercus robur. The gall is attracts your attention with its red and white pattern. The galls are only a half or one centimeter in size. The galls seem round, but they are somewhat flattened underneath.

The sexual Spring generation grows from the sleeping buds on the trunk of oak. They look a lot like the Spring galls ofCynips quercusfolii, but are more green to grey, with clear white to brown hairs, the hairs usually a little longer than C. quercusfolii.

Picture: K. Boele

Cynipsquercusfolii onQuercus roburand Q. petraea is what the Dutch definitely call Gall Apple. This shiny gall, from the asexual generation of this gall wasp, is 1-2 cm and pale, pink, yellow and red, later brown. Sometimes the galls are warty (onQuercus petraea) or smooth (on Q. robur). Sometimes it had bulges or projections on one or more sides, caused by other parasites. The gall is very common and some years the leafs of oak are carying up to four or more. There is one gall chamber in each gall, right in the middle. The wasps emerge in November-December, when the galls have fallen from the leaves.

The sexual generation emerges from galls in the buds (see botom pictures), where the buds form to be 5 mm high (usually smaller), covered with dark purple to violet velvet.

female agamic generation

Picture: E. Jacobs

on Quercus lusitanica

sexual generation, Pictures: R.J. Koops

Diastrophus rubi can be found on brambles, raspberry and dewberry. The gall contains many gall chambers and the swelling in the stem is fusiform or cilindrical. The gall surrounds the whole stem. The galls are 10 mm by 20 to 100 mm. The galls are usually pale green and they are bald. The species hibernate in the gall and emerge in the following Summer.
Picture: H. Jonkman

Diplolepis mayriis a spiny gall on similar rose species asDiplolepis rosae. The galls are usually found as a group of coalesced galls growing from leaves and flower buds and on the stems. They are 0,5 to 4 cm and sparsely covered with short spines. The galls are usually rusty brown to dark brown, but may be bright red when formed on the fruit. The inquiline associated with this gall wasp isPericlistus brandtii. The galls contain many gall chambers.

Pictures: E. van den Ham

Diplolepis rosaeyou can find on many roses likeRosa caninaR. glaucaR. micranthaR. pimpinellifolia,R. rubiginosaR. tomentosa(Docters van Leeuwen (1982)). I often find them on R. canina. The galls develop at different places on the plant, but usually you can find them on the tops of branches, were they can become as large as five centimeters. The galls are globules with lots of hairy spiny little branched branches sticking out. The galls can be red, green, yellow, violet or pink. Inside is rigid and several chambers can be found. In all these knots and bunches of branches you can also find other organisms living there lives, like earwigs or hyperparasites.

Picture: E. Jacobs

Picture: H. Jonkman

Diplolepis spinosissimae I found in June 2002 in the dunes of Norderney onRosa spinosissima . sadly I was not able to take pictures, but it was a wonderful sight. The roses were the same size as the short grass, so I had a very good view of a field covered with red dots, caused by this Diplolepis. The galls are irregularly shaped (sort of globular) and green or red and up to 6 mm in size. But they can be much larger as well. They appear on both sides of the leaves, usually on the midrib. The galls can also be elongated, smooth or with small spines. You can find them in most places where R. spinosissimagrows naturally.
Picture: H. Pras

Liposthenes glechomaecauses round shapes to appear on the leaves ofGlechoma hederacea. The galls make the leaves disappear completely sometimes. The galls are not so rare, but you have to look and check under every ground-ivy you see. The galls are green and hairy and round or oval shaped. Often several galls form one big gall. It is worthwhile to examine the inside of a gall. Here you can find a few hard round little balls that are fixed in a frame of filaments called parenchyma cells.

Picture: B. Kabbes

Neuroterus albipes The agamic generation causes the Smooth spangle. A small, round disc usually growing on the upper side of the leaves of Quercusrobur. They can be found in many colours, from white to green to purple or red or pink. Especially later in the season they can be cup shaped, because the edges curle upward in a irregular fashion.

The sexual generation consist of very small galls, 1,5-2 mm long and 1-1,5 mm wide, and is positioned on the edge of the leafs, usually near the base, in Spring from early May. The galls are attached by the long side to the edge of the leaf and are white or green. They sometimes appear to be attached to the main vein, because the leaves can be very poorly developed.

Picture: M. Meijer

Sexual Spring generation

Neuroterus (Andricus) anthracinus (ostreus) cause little oyster-like galls to appear on the main vain of the underside of the leaves ofQuercus robur. When the gall is old and the oyster has fallen on the ground, only the two valves of the oyster remain on the leaf. The round shape you can find earlier in between the valves is yellow-green and oval, often covered with many tiny red dots.

Picture: M. Meijer

Neuroterus politus (aprilinus) is a wasp inducing galls in the bud of oak in early Spring time, for its sexual generation. On the 8th of May 2006 I found these galls (pictures on te right) on english oak (Quercus robur) in Haren, just south of Groningen. The galls can grow to be 10 mm tall. The gall is bright green, exept for the scales, who remain brown. The gall usually appears just before the oak buds start to sprout. The agamic generation causes galls in the catkins of oak.

Neuroterus querusbaccarummakes the young leaves and the filaments of the flowers ofQuercus roburdevelop shining green watery marbles. The galls shrivel completely if they are laid to dry for a while. I know I should have taken pictures immediately. The leaves and filaments were covered with the little globules. It was a magnificent sight. 

Tetramesa hyalipennis is a black coloured wasp that causes rather large galls on Elytrichia juncea subsp. boreoatlantica(or Elymus farctus). The internodes are strongly shortened and thickened. The leaves are broadened and remain short. The larva lives in the merrow. The gall is strong and sollid and sometimes bend slightly.

Trigonaspis megapteracauses Spring galls from sleeping buds on the base of trunks on oak trees, also often on one year old branches. Often the galls are growing unseen under moss and soil. The galls look juicy and are uasually pale pink and white or dark pink or reddish. The galls are round and 3 to 10 mm and appear in April, early May. The wasps emerge in May, early June. Unfortunately the galls can not be distinguished from another species,Trigonaspis synaspis. This gall is said to be much more rare and growing more inconspicious under mosses and soil. The agamic Summer generations of both species are easily to distinguish, so a simple Summer check should sort out this identity problem.

sexual Spring generation, Pictures: R.J. Koops