Common spangle galls on Oak leaf

Common Spangle Galls are seen in late summer or early autumn on the underside of oak leaves almost anywhere on the farm. They are caused by the gall wasp Neuroterus quercusbaccarum. A single leaf can have up to 100 galls, each of which contains a single developing wasp. The galls drop off the leaf in late autumn and the ground below some oak trees can be littered with fallen spangle galls (thrushes and Wood Pigeons apparently eat them with relish, though I’ve not witnessed that myself yet). The larvae continue to develop inside them, and in spring the females emerge to lay their eggs on oak catkins.