8 to10 mm. The abdomen in Apethymus serotinus is entirely black. The antennae are black with segments six to eight white in the female and also sometimes in the male. The hind tibiae are white basally contrasting with the black apices.

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.

Associated with Oak.

Flight period: September to November.

This species overwinters as an egg on oaks. Eggs are inserted into the bark of twigs and the larval Apethymus serotinus feed on the young leaves.

Widespread but local in England and Wales.

Status in Leicestershire and Rutland not known.

https://www.sawflies.org.uk/apethymus-serotinus/