Oak Apple, Rutland Water, Photograph
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 2-5cm. Oak apples are caused by chemicals injected by the larva of certain kinds of gall wasp in the family Cynipidae. The adult female wasp lays single eggs in developing leaf buds. The larvae feed on the gall tissue resulting from their secretions. Considerable confusion exists in the general 'literature' between the oak apple and oak marble galls. The oak marble is frequently called the oak apple due to the superficial resemblance and the preponderance of the oak marble gall in the wild.
Some common oak-apple forming species are Biorhiza pallida gall wasp in Europe, Amphibolips confluenta in eastern North America, and Atrusca bella in western North America.
Oak apples may be brownish, yellowish, greenish, pinkish or reddish.
