A spongy spherical gall which forms on oak trees in response to the developing larvae of a gall wasp.
The wasp is Biorhiza pallida (in Europe) or Amphibolips confluenta (in America), family Cynipidae‘Oak apple galls are sometimes mistaken for an actual crop of the tree, such as apples on on apple tree, but are actually deformed leaves.’
- ‘An oak apple is also known as an oak gall.’
- ‘The so-called oak apple, a round, spongy, fruitlike object about 2.5 to 5 cm (1 to 2 inches) in diameter, is caused by the larvae of the gall wasp Biorhiza pallida.’
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