The Probert Encyclopaedia of Nature

GALL-FLY

Gall-fly is a name for several hymenopterous insects of the family Cynipidae, which form galls, each species preferring a different plant. The gall is due to an irritating fluid which the insect deposits on the plant along with its egg. The large galls at the base of oak leaves are produced by the Cynips quercus baccarum, a fly of a brown colour, with blade antenna, chestnut-brown legs, and white wings. The small galls on the under surface of oak leaves are due to another species, Cynips quercus folii, those on the stems of oaks to Cynips terminalis.
Research Gall-fly