Following on from blue Ormyrid wasps and green Torymid wasps on knopper galls, we now have brown Cynipid wasps on knopper galls. Comparison with photos here and here shows a good match with Synergus reinhardi but, to be on the safe side, I will tentatively identify it as Synergus sp. (Hymenoptera: Cynipidae) for the time being.
These wasps lay their eggs in the knopper gall but, unlike they Ormyrid and Torymid wasps, their larvae do not attack the resident gall-causing larvae directly, they just occupy the same cavity. Organisms that practice this benign form of parasitism are termed inquilines.
Photos taken in Whiteknights Park, Reading University grounds, Reading, UK, on 2009-10-04.