Callirhytis flora (Hymenoptera: Cynipidae)
Live Oak Petiole Gall Wasp
Approx 1 mile north of Mill Creek Road, along dirt road in North Cow Mountain area., Mendocino County, California
October 14, 2013

Host is Quercus agrifolia or Q. wislizenii. Two exit holes of wasps are visible in this image. The acorn was later cut open, and more wasps and wasp larvae were found inside.