The urchin gall wasp (Antron quercusechinus) is a cynipid wasp that induces galls on oaks and exhibits an alternation of generation. In the spring a sexual generation emerges from a bud gall. The males and females of this generation induce a unique leaf gall from which a parthenogenic female generation emerges about November. Shortly after emergence the fall, the females oviposit in a leaf bud to begin the cycle anew.
The monothalamic (one chambered) spring bud galls of the urchin gall wasp are difficult to identify because they simply look like swollen leaf buds. However the summer/fall leaf galls are fascinating. These unisexual galls are found on the undersides of oak leaves with several usually occurring per leaf. Also monothalamous, the unisexual galls are red, purple or pink. White-tipped spines radiate outward over the entire gall, making it look like a sea urchin. Usually pointed, the spines are sometimes clubbed at the tip. The “urchin” galls are detachable and either fall off in the wind or drop to the ground with the leaves when the leaves fall. I love these galls!
These urchin wasp galls were photographed along the shore of Crystal Lake (Shasta County CA). More information about gall formation can be found in the post entitled “Oak Gall Wasp” posted on 09-08-11.