Oak apple gall

Oak apple is the common name for a large, round, vaguely apple-like gall commonly found on many species of oak. Oak apples range in size from 2–5 cm in diameter and are caused by chemicals injected by the larva of certain kinds of gall wasp in the family Cynipidae.[1] The adult female wasp lays single eggs in developing leaf buds. The wasp larvae feed on the gall tissue resulting from their secretions