Callirhytis quercussuttoni (Hymenoptera: Cynipidae)
Knowland Park, Oakland, Alameda County, California
November 7, 2021

Old stem gall caused by gall wasps on Quercus agrifolia. The wasps have long ago emerged, leaving exit holes. Gall here was sawed in half to expose the larval chambers where the wasp larvae developed and pupated. There was also some other insect activity inside the gall, likely moths. The upper part of the gall as viewed in this image contained a lot of frass which the gall wasps don't leave. Note the messy borders of the space along the top of the gall versus the neatly rounded larval cells of the gall wasps below. The frass and other debris has been cleaned out so the internal structure of the gall is easier to see.