Gallfly

from WordNet (r) 3.0 (2006)

gallfly
    n 1: small solitary wasp that produces galls on oaks and other
         plants [syn: {gall wasp}, {gallfly}, {cynipid wasp},
         {cynipid gall wasp}]
    2: fragile mosquito-like flies that produce galls on plants
       [syn: {gall midge}, {gallfly}, {gall gnat}]
    3: any of various insects that deposit their eggs in plants
       causing galls in which the larvae feed

from The Collaborative International Dictionary of English v.0.48

Gallfly \Gall"fly`\, n.; pl. {Gallflies}. (Zool.)
   An insect that deposits its eggs in plants, and occasions
   galls, esp. any small hymenopteran of the genus {Cynips} and
   allied genera. See Illust. of {Gall}.
   [1913 Webster]