Size 2 to 3.5 mm, the sexual generation male and females wasps are a golden chestnut colour. The agamic wasps are larger, and wingless. 

Oak-apple galls are caused by the sexual gneration of wasps.  They are large and spongy, pale green becoming cream/pink or red, and later brown; they persist as old galls over winter.  Inside are multiple larval chambers.  The agamic galls are on the roots, and thus rarely recorded.

Use this for recording the wasp gall causer; provide detailed photographs.  If it has emerged from a gall, photograph the gall.  If you are recording the oak-apple gall, submit as Biorhiza pallida f. sexual

Oak-apples 

Adults emerge from the Oak Apple Galls in June and July.

Quite common and widespread throughout Britain.

Common