gall wasp

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various wasps of the family Cynipidae whose larvae produce distinctively shaped galls on oaks and other plants.

from The Century Dictionary.

• noun A hymenopterous gall-insect; one of the Gallicolæ, Cynipidæ, or gall-flies.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any insect of the Cynipidae family, whose larvae damage trees, particularly oak trees, creating galls on the branches.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun small solitary wasp that produces galls on oaks and other plants