“Oak apple day, the 29th of May,” is a rhyming reminder of the public holiday ordered by Charles II to celebrate the restoration of the monarchy in 1660. After his escape from parliamentarians by hiding in an oak tree at Boscobel in Shropshire, it is no great leap of imagination to associate a hidden king with oak apples: parasitic galls are strange, uncanny fruit that encourage satire at least.
A month ago, the oak galls on this ancient tree were as shiny as cherries. Today they are bigger, browner and mottled, like weird little apples. They were formed when an agamic, wingless, female oak apple gall wasp, Biorhiza pallida, burrowed out from a gall in the oak’s roots, climbed the tree and injected a cluster of eggs and a drop of venom into a leaf bud. The hatched grubs then produced substances that caused a tumour-like effect on the oak cells, forming the apple, inside which the larvae fed in their chambers.
