This time of year oak trees are winding down for the season. Next years miniature leaves are wrapped in buds, nutrients are being pulled from the leaves and root systems are being managed for a coming winter season. But what are those funny spots on the leaves? What are those strange round balls underneath the leaves? What are those mini artichoke shapes on the buds? These are galls. Galls are the product of gall wasps. Not wasps like the big black and yellow ones that sniff around our fruit drinks in late summer but something much smaller . None of these wasps can hurt us, some of them are extremely small, smaller than midges. Different types of wasps lay different types of eggs into different parts of oak trees and other trees. The egg is laid along with a fluid that brings on the growth of a gall. Over 50% of gall wasps lay their eggs in oak trees.
Below are pictured a few common oak tree galls that can be found around Donegal at the moment.
The small round brown spots are spangle galls. Inside the larvae of an asexual female waits for spring, where it will hatch and lay eggs into the male catkins or the leaves of the oak tree. Current galls will grow and out of them will emerge male and females which breed and so the cycle continues.
The larger green round galls are current galls, with either males or females developing inside.
These are called artichoke galls or hop galls. Inside is an asexual female waiting for spring. She will lay eggs in the catkins of oak, forming hairy catkins galls, which have either male or females inside, which in turn will lay eggs into leaf buds forming next years artichoke galls.