An Oak Gall New to Britain

The checklist maintained by the British Plant Gall Society lists 90 different galls on oaks, caused by cynipid wasps. To that list must now be added a new arrival, an asexual gall of the cynipid wasp Andricus coriarius, discovered and described by Maria Fremlin and two colleagues (Cook et al. 2026). It was first noted as an attached specimen in September 2025 on a pedunculate oak (Quercus robur), estimated to be around 100 years old, in Alexandra Park, London. In October of the same year, Maria found a single gall on a 25-year-old Portuguese oak (Q. faginea) on the campus of the University of Essex, and a later search revealed further galls on specimens of cultivars of Algerian oak (Q. canariensis ‘Latifolia’) and Medlar-leaved oak (Q. petraea Mespilifolia Group). 

All of these host trees are white oaks, Quercus Subgenus Quercus Section Quercus. The galls of the sexual generation, which have yet to be discovered in Britain, appear to be restricted to oaks of Subgenus Cerris Section Cerris in Continental Europe. Andricus coriarius is believed to have its main center of population in southeastern Europe but it has been spreading steadily to the west and north, and is now considered to be common in the Netherlands and Belgium.

The three oaks that Maria investigated are part of the Wivenhoe Park Millennium Oak Collection, about which she wrote for the Society in 2019. Her article can be found here.

Work cited

Cook, P., M. Fremlin, and J. Bowdrey. 2026. Asexual galls of the cynipid wasp Andricus coriarius (Hartig, 1843), new to Britain. Cecidology 41(1): 2–9 [link]