Feron atrimentum (Hymenoptera: Cynipidae)
Striped Volcano Gall Wasp
near Regency Gate, Mt Diablo State Park, Contra Costa County, California
September 4, 2015

Host is Quercus douglasii (blue oak). This is a spring, bisexual generation gall of this species, cut open to show dark larval chamber. The wasp has already emerged.