Andricus quadrilineatus f. agamic

The agamic galls are formed on catkins or on leaves.  On catkins, they are grooved, egg-shaped galls without hairs, which turn from green or yellow to dark red as the season progresses.  On leaves the galls are small and pip-shaped with a pointed tip, at the end of the midrib or lateral vein.

[Note: the sexual galls are formed on catkins; they have a brown tip and tuft of white hairs, with the remains of the anthers at the base.]

Other small galls can be present on oak catkins and leaves

Photograph the gall on oak, and note the host species

native oaks 

Unlike many gall-wasps on oak, the agamic generation of catkin-galls is formed by the wasps in Spring - this is because it is dependant on the anthers of the male catkins.  The larva hibernates in the fallen gall.  The sexual galls also appear in Spring, also on catkins, but have not been recorded in VC55.  The sexual generation of galls may be missed, with the agamic generation giving rise to a consecutive agamic one (see Bladmineerders webpage, accessed 06/05/2025) .   

Common (British Plant Galls, Redfern & Shirley, 2023)

occasional; probably under-recorded

See British Plant Galls (Redfern & Shirley, 2023) and Bladmineerders (Plant Parasites of Europe) webpage