Length 2-3mm. Antennal toruli (antenna sockets) are positioned low on the face, at or below the level of the lower margin of the eyes. Female antennae have 5 or 6 funicle segments and a 3-segmented club (clava); male antennae have 6 funicular segments and a 2-segmented club. The clypeus is convex with a curved anterior margin, and they possess 4-toothed mandibles. The notauli (the longitudinal grooves on the mesoscutum) are complete and relatively deep. The body surface is largely smooth or exhibits a very shallow, delicate reticulate (net-like) patterning, giving them a distinct metallic green, blue, or bronze sheen. The forewings have a distinctly long, thick marginal vein; the postmarginal and stigmal veins are short by comparison. 

50 UK species, very difficult to identify.

Unless identified by a recognized expert, explain how the specimen was identified and submit photos of key features. 

The majority of Gastrancistrus species are parasitoids of Diptera, often Cecidomyiidae (gall midges). 

Widespread.

Unknown.