The adult is very dark - metallic blue in a good light. It has dark legs (distinguishing it from Arge ustulata), smoky wings which lack a wing cloud.

Arge ustulata has pale legs and a wing cloud. There are other dark-bodied Arge species that could potentially be found in Leicestershire and Rutland.

• dark bodied (metallic blue)
• all dark legs
• tinted wings without a wing cloud
• black hairs on face

To be found on berberis and mahonia plants.

June to August

Berberis sawfly larvae cause severe defoliation on some berberis and mahonia spp. in Britain. They have a black head on a greyish-white body with yellow blotches and small black dots.

First British record was in Essex in 2002, since when it has been recorded in most southern counties, and has reportedly now reached Yorkshire.

Previously uncommon in Leicestershire and Rutland, its numbers now seem to be increasing.

https://www.sawflies.org.uk/arge-berberidis/