Do you know your Knopper from your Common Spangle?
No, we haven’t gone mad. We are talking about Oak Galls! ‘What on Earth are they?’ you may ask (or perhaps you are already in the know). Luckily, you can read on to find out (and never walk past an Oak tree again without having a look to see if you can spot one!)
What is a gall?
A gall is defined as a growth on a plant that is made of plant tissue but caused by another organism. These organisms might be insects, bacteria, fungi or viruses and insect galls are the most common. All galls are formed for the same sort of purpose: the deformity is a deliberate action by the ’causer’ to use the plant for its own purposes. The gall causer manipulates the plant tissue for itself, but the plant receives no benefits in exchange. Most galls don’t harm the plant though and will have no effect on the health of the host trees.
The mighty Oak has a number of different galls and our amazing volunteer Warden, Tim Hewke, has been documenting those he has seen while out and about in the woods in Kent. Do you know which is which? Take a look at our mini quiz below, jot down your thoughts and scroll down for the answers. No cheating! Good luck and happy gall spotting!
Many thanks again to Tim Hewke for his beautiful photography and gall ID skills.
A – Artichoke Gall – Artichoke galls, caused by the wasp Andricus foecundatrix can be seen from mid-summer and mature in August where the inner gall is forced out, falling to the ground. The single larvae that is housed inside will pupate in the fallen gall, emerging next spring.
B – Knopper – The knopper gall is found mostly on pendunculate oaks in England and Wales. The wasp, Andricus quercuscalicis, lays its eggs on the freshly pollinated flowers of the oak, causing the offspring to deform the acorn for its own uses. This gall develops over the summer and falls to the ground in autumn when the larvae emerge.
C – Marble – Oak marble galls are caused by another gall wasp, this time Andricus kollari. The marble gall is found on pendunculate oaks. The wasp was intentionally introduced from the Mediterranean in the 1800s because its galls have a high tannin content, which was useful for tanning leather and dyeing cloth. The gall should have little dimples on its surface. Inside, the wasp larvae are protected from bad weather by the woody outer shell and the tannins.
D – Silk button spangle – There are four types of spangle gall in the UK, caused by four different gall wasps. All four look very similar, although if you look very closely they have different surface structures. They are found throughout the UK on both our native oak species, although they also like other oak species. The galls appear in spring when the wasp lays their eggs on the new leaves, and the larvae emerge during the summer.