The cynipid wasp Neuroterus quercusbaccarum has both agamic and bisexual generations which cause different galls to occur on Oak. The gall is more likely to be seen than the adult wasp.
Photo ID? Easily identified from a photo
Anywhere that Oak is present.
When to see it
As described below.
The male and female of the bisexual generation emerge in June from Currant Galls which are spherical, smooth, succulent, berry-like galls up to 7 mm in diameter which vary in colour from pale yellow through green to red or purple. These galls may occur on Oak leaves or catkins. After mating the fertilised eggs are laid by the sexual generation in the lower epidermis of the Oak leaves. The Spangle Galls develop over the winter and the insects emerge in April, laying their eggs in the catkins or lower epidermis of leaves. The cycle, an alternation of generation, then begins again… Naturespot