Leaf galls. Spherical galls on an oak leaf. These galls are produced by the common oak gall wasp, Cynips quercusfolii. A parthenogenetic generation of female wasps emerge from these galls in early winter and they lay their unfertilized eggs in un- developed oak buds. The larvae hatch and produce small galls from which males and females emerge in early summer. After mating the females lay their eggs on the underside of oak leaves. Galls form because the developing larvae produce substances which stimulate tumorous growth in the surrounding plant tissue. The masses of tissue provide the larvae with a food & protection from predators.