Wool Sower Gall
The wool sower gall is caused by secretions of grubs of a small gall wasp, Callirhytis seminator. The wool sower gall is specific to white oak and only occurs in the spring. The galls contain seed-like structures. The gall wasps develop inside these structures. (This gall is also called the oak seed gall.) Fortunately, wool sower galls are usually never abundant so that the health of infested trees is rarely threatened.