What Google Knows
Oak apple or oak gall 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 to 4 centimetres in diameter and are caused by chemicals injected by the larva of certain kinds of gall wasp in the family Cynipidae.
- oak apple:
n oak gall caused by larvae of a cynipid wasp