A black, slow moving species with dark wings. The legs are covered in fine, pale hair and sometimes the front legs are piceous. Identification relies on wing venation features and other small anatomical details.

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.

Often most numerous in city locations, but any areas where Ash, the larval foodplant, occurs.

Flight period: April to June.

Larvae feed gregariously on the native Ash Fraxinus excelsior.

Widespread in Britain. Outbreaks of large populations have become more common in recent years defoliating trees, especially in city locations such as Telford, Manchester and Aberdeen.

Rare or under-recorded in Leicestershire and Rutland. The Cloud Wood record below is the first for VC55.

https://www.sawflies.org.uk/tomostethus-nigritus/