The World of Apples

The apples that aren't

Oak apple

Biorhiza pallida, Cynipidae, gall wasps

An oak apple is not a fruit but a gall: a round, spongy growth on an oak leaf or twig, caused by the larvae of a gall wasp2. In Britain it is made by Biorhiza pallida, which is quite common and widespread3. Wingless females of one generation hatch from galls on the oak’s roots, climb the tree and lay their eggs in a leaf bud; the grubs make the bud swell into the apple, and feed in chambers inside it4. The galls are pale green, becoming cream, pink or red and later brown, and in Britain the winged wasps come out in June and July3. Other wasps, fungi and microbes live in them too4.

The 29th of May was once Oak Apple Day, a public holiday ordered by Charles II to celebrate the restoration of the monarchy in 1660; he had escaped the parliamentarians by hiding in an oak at Boscobel, in Shropshire4.

German calls such a growth a Gallapfel, a word found from the fifteenth century, especially for galls on oaks and willows5. In colonial Australia, “oak apples” were something else again: the cones of Casuarina stricta6.

Sources

  1. GBIF Backbone Taxonomy: Biorhiza pallida, Global Biodiversity Information Facility. Supports: the accepted name; an insect of the family Cynipidae.
  2. oak apple, American Heritage Dictionary of the English Language, fifth edition, HarperCollins, 2022. Supports: a round spongy gall on an oak leaf or twig, caused by the larvae of certain gall wasps.
  3. Oak Apple Gall Wasp, Biorhiza pallida, NatureSpot, Leicestershire and Rutland. Supports: the galls made by the sexual generation, large and spongy, pale green becoming cream, pink or red and later brown, with many larval chambers; the agamic galls on the roots; adults emerging in June and July; quite common and widespread throughout Britain.
  4. Country diary: Today was once a public holiday, thanks to these oak 'apples', Paul Evans, The Guardian, 29 May 2026. Supports: the wingless female climbing from a root gall to lay eggs in a leaf bud, and the grubs forming the apple; the galls "like weird little apples"; other wasps, fungi and microbes living in them; Oak Apple Day, 29 May, ordered by Charles II for the restoration of the monarchy in 1660, and his hiding in an oak at Boscobel.
  5. Gallapfel, Digitales Wörterbuch der deutschen Sprache, with Wolfgang Pfeifer's Etymologisches Wörterbuch. Supports: Gallapfel, an apple-shaped growth on the leaves of broadleaved trees, especially oaks and willows, recorded from the fifteenth century.
  6. Austral English: a dictionary of Australasian words, phrases and usages, entry Apple, Edward E. Morris, Project Gutenberg, 1898. Supports: oak apple as an Australian name for the cones of Casuarina stricta.