Colin Varndell / Knopper gall of the gall wasp (Andricus quercuscalicis) Dorset, England, UK, September.

Colin Varndell / Gall on oak acorn made by larva of Knopper gall wasp (Andricus quercuscalicis), Dorset, UK, August.

Chris Mattison / Knopper Oak gall remains, caused by the wasp (Andricus quercuscalicis) Forest of Dean, Gloucestershire, UK May

Solvin Zankl / Knopper gall (Andricus quercuscalicis) on oak tree acorn, and Common spangle gall (Neuroterus quercusbaccarum) on oak tree leaf. Bavaria, Germany

Adrian Davies / Knopper galls on English oak (Quercus robur) acorns, Knopper galls are chemically induced distortions caused by gall wasps (Andricus quercuscalicis) laying eggs in the acorn buds, Surrey, England, UK,...

Chris O'Reilly / Gall on oak acorn made by larva of Knopper gall wasp, UK

Linda Pitkin / Common oak (Quercus robur) acorns with Knopper galls, caused by Knopper gall wasp (Andricus quercuscalicis). Surrey, UK. August.

Andy Sands / Knopper Gall wasp (Andricus querecuscalicis) newly emerged adult on bud of turkey oak, this wasp lays eggs in early spring among the buds of Turkey Oak then the offspring lay on Pendunculate Oak to pr...

Will Watson / Knopper galls on English Oak (Quercus robur), caused by the gall wasp (Andricus quercuscalicis), hedgerow, Worcestershire, England, August.