oak apple
noun
1- a spongy spherical gall which forms on oak trees in response to the developing larvae of a gall wasp没食子, 栎五倍子。
1.1
- The wasp is Biorhiza pallida (in Europe) or Amphibolips confluenta (in America), family Cynipidae.这种蜂是（欧洲的）没食子瘿蜂或 （美洲的） 汇网纹瘿蜂, 瘿蜂科。