DURING the last few weeks, when on events or just walking through the nature reserves carrying out patrols, I have been stopped and asked about the strange lumps, bumps and nodules that can be seen in amongst the leaves of the oak trees. These lumps, bumps and nodules are often, unsurprisingly, thought to be some sort of disease. However, this not the cause of these deformities, they are called by gall wasps. When the word wasp is mentioned the mind immediately jumps to bad memories of our yellow and black friends causing a nuisance when we are trying to enjoy a summer’s picnic. This however, is not the case Gall wasps are extremely different.

They are a small ant like creature, the majority of the species that create the galls found on oak trees are winged but some species can be wingless. Nearly all species of gall wasps induce gall formation in plants, especially in oaks. The galls are created by the gall wasp laying its egg in a various part of the plant. The hatching of the egg then acts as a catalyst for the plants tissue to swell up around the grub or grubs to form the gall.

The gall then acts as home for the grub providing it with food shelter and protection. However, there is a darker side to some of our gall wasps. Some species do not actually create their own gall, instead they make use of the nice cosy galls that have already been formed by another species. They will lay their egg in the host gall and when the egg hatches it will feed on all the tissue that forms the gall which was originally intended for the host grub.

If the host gall does not die due to the lack of food more often than not the invading grub will eat them anyway. So if you are ever lucky enough to witness a gall wasp emerging from a gall it is important to remember that it may not be the species that originally created it. That’s right folks, it is true what they say, you can’t judge a gall by its cover.

So what is the different gall that you may be seeing in our oak trees. The first gall that I ever noticed is a green colour, later turning to green, looks a little like a shelled walnut and is formed on the acorn of the oak tree. This is called a Knopper gall and has become widespread in Britain since first appearing in 1960. Another very common gall is the Marble gall and like its name suggests it is round like a marble. They are formed by the egg being laid in the bud of the oak tree.

These galls have spread from southwestern Britain since introduction in the 19th century. A very similar species to the one that creates the marble gall creates another gall named due to the way it looks and that is the artichoke gall. This again is laid in the bud of the oak and causes the bud to form into a mini artichoke. The last group of galls I will mention is the spangle galls.

These are much smaller that the galls I have previously mentioned and can be found on the undersides of the oak’s leaves. There are three different types; the common spangle which looks a bit like the nobble on top of a battery but green and red, the smooth spangle which is very similar but a bit flatter and a bit redder and the silk button spangle which is similar in size but looks less red and has a dimple. So next time you are out and about and you pass a oak why not have a close look and see how many galls you can see.