An oak apple on a twig of English oak (Quercus robur), in May, UK. The picture shows a gall developing from a dormant leaf bud, with a normal bud to its right. The gall retains remnants of the scales that covered the bud, as a cone-like tip (left, brown). The gall is segmented; this results from the structure of the bud before the gall started to grow. The gall tissue (white with a red covering) is soft and spongy at this stage.Oak apples are produced when an asexual female gall wasp, Biorhiza pallida, lays eggs inside a dormant bud. She drills into the bud with her ovipositor to make a series of tunnels. She then lays up to 100 eggs in each, a process that can take several hours. The eggs develop into larvae, then male and female wasps. These sexual females lay eggs in the roots of the tree, also producing galls. The root galls give rise to asexual females, and the cycle is complete.