Length 7 to 11 mm. This species has a black head and thorax but an orange abdomen and is characterised by the very long antennae, the black tarsi and the combination of a yellow costa and black stigma. This species flies as an adult late in the season, September to November. The larvae are rather plain, coloured two-tone grey.

To be seen around Oak - the larval foodplant.

Larvae are found in May and June, the adults flying in September and October.

Thought to be widespread and fairly frequent in Britain although there are very few records.

Rare or under-recorded in Leicestershire and Rutland.

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