Callirhytis eldoradensis (Hymenoptera: Cynipidae)
Mitchell Canyon, Mt Diablo State Park, Contra Costa County, California
November 27, 2015

The growth of this Quercus agrifolia acorn was stunted by a gall wasp. The wasp has already developed and left. The acorn has been cut in half to show the larval chamber (marked by the arrow). The larval chamber of the wasp is under the cap but outside the embryo of the acorn.