Gall

Description:

Gall on a tree likely made from a gall wasp.

Notes:

From Wikipedia: Gall wasps, also called gallflies, are a family (Cynipidae) of the order Hymenoptera and are classified with the Apocrita suborder of wasps in the superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1300 species of this generally very small creature (1-8 mm) are known worldwide, with about 360 species of 36 different genera in Europe and some 800 species in North America.