This is quite a small but very distinctive sawfly which I regularly see around my back garden. Brightly orange body and legs, a black head, black markings on the thorax and along one side of the wings.
Common and widespread, the larvae are considered to be an occasional but serious pest of crucifers, especially turnips.
Turnip Sawfly (Athalia rosae), rear garden, Staffordshire, England. May 2017.