Galls, Diseases, and Pests - California Oak Gall Wasp
Andricus quercuscalifornicus
California Oak Gall Wasps lay their eggs on oak branches in the Fall, and the larvae hatch the following Spring. The larvae cause the galls to form rapidly. As the galls dry, they harden and turn brown. In the late Summer or early Fall, the larvae pupate and bore their way out of the galls.
This gall shows signs of damage on the outside.
But the larvae inside are still intact.
Notice the small exit borehole in the gall on the right.
Many exit boreholes in this gall. And a photobomber on the left!
Other parasites often enter the gall and use the gall as a food source. And birds often will try to get to the tasty larvae. Either may explain the large cavities in these galls.