Female: 6.5 to 8 mm, male: 5 to 6 mm. The female is yellow with a black frontal ocellar spot and black on the occipital field, mesonotum, sometimes the scutellum in the middle, the prosternum, and most of the mesosternum. In the male the head is black with yellow on the labrum, clypeus, behind the orbits, and the interantennal crest. The antennae are often brown on the underside. The thorax and abdomen are yellow with black on the sternum, mesonotum, metanotum, mostly that scutellum and more or less the dorsum of the abdomen. The legs are yellow with black on the hind tibiae apices and the tarsi.

Adult Larva

Adult: Unless identified by a recognised expert, a photo is required and the specimen should be examined with a microscope. In the comments box, state the key or ID method used and describe the size and identifying characters.

Larva: Unless identified by a recognised expert, a photo is required. If the photo doesn't show the key ID features then in the comments box describe the size and identifying characters you have observed.

Particularly associated with willows.

Adult flight period May to June, July to September.

The larvae feed on willows and sometimes birches, hazels, poplars and elms.

Local in Britain.

Rarely recorded in Leicestershire and Rutland.

https://www.sawflies.org.uk/euura-melanocephalus/