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 area around its exit hole has been carved away to better expose the larval chamber for this image. The larval chamber of the wasp is under the cap but outside the embryo of the acorn.