With heavy cloud and occasional rain, Sunday was not a day for finding butterflies in the woodland. So, I decided to look more closely at Oak leaves to see what I might find, and that strategy paid off in spades as the next few days’ blog posts will show. First up, I found a gall I hadn’t seen before, which turns out to be the sexual generation of the gall wasp Andricus curvator.
When the adult wasps emerge in the spring from the agamic (asexual) generation galls, which are formed on buds in the autumn and fall to the ground to over-winter, they lay their eggs mostly on Oak leaves but also, sometimes, on twigs or catkins, so these galls can take several forms. The ones I found (and they were numerous) were all on leaves, causing malformations and swellings, as you can see from the photos above and below.
I was tempted to split a gall open to see what was inside but it turns out I didn’t have to, as something had nibbled away at one gall, revealing a second round gall inside (see below). The larvae within this inner gall will emerge in the autumn to lay its eggs on Oak buds, and so the process will continue.