Blister Gall - Neuroterus numismalis f. sexual

Neuroterus numismalis is a gall wasp that has two generations per year.

The sexual generation causes a circular Blister Gall that is visible on both sides of an Oak leaf.  It is about 3mm across; green at first then brown.  The blister has lines radiating from the centre and the exit hole may be in the upper or lower surface.

Under "Species", please select "f. agamic" or "f. sexual" as appropriate.  Provide photographs of the gall on the host plant, and note the host species.

English, Sessile and Turkey Oaks.

Spring

The Silk-button Galls are the agamic generation and can be seen from August to October, until the leaves fall in autumn. Each gall contains a single cell holding one wasp. The larva will mature in August but remain in the gall on the ground throughout the winter, emerging the following year from February to April.

The females that emerge in spring lay their unfertilised eggs on Oak leaves, causing the Blister Galls of the sexual generation.  Male and female wasps emerge from the Blister Galls in mid-summer and their fertilised eggs result in the next generation of Silk-button Galls.

Common and widespread in Britain.

Common in Leicestershire and Rutland but recorded less often than the agamic form. 

See British Plant Galls (Redfern & Shirley, 2023)