01/09/2025
This wrinkly mutant acorn known as Knopper Galls and are made by the Gall Wasp Andricus quercuscalicis, which looks like a tiny black fly just a few millimetres long. Early in the summer, the female Gall Wasp laid eggs on the buds of developing acorns and a fascinating transformation was triggered as soon as they hatched: responding to a chemical signal released by the larvae, the oak tree was persuaded to sculpt its tissue into knobbly Knopper Galls in place of normal acorns.
Knopper Galls are greenish-yellow and sticky at first but ‘ripen’ to a woody brown in early autumn, at which point they drop to the ground. The larvae pupate inside and spend the winter tucked up in their galls before emerging as adults the following spring.
