Turnip sawfly, this + 7 mm large sawfly is black with a yellow/orange abdomen.
Turnip sawfly (Athalia rosae). This + 7 mm sawfly is black with a yellow/orange abdomen. The caterpillar-like larvae live off the leaves of mainly blackberries and raspberries; the adult wasps feed on nectar and pollen.
The larvae are usually on the underside of the leaf and feed on the chlorophyll between the veins. The larvae are black to dark green and over 20 mm long. The larvae (caterpillars) hibernate underground and emerge as adult wasps in early summer.
As a rule, the larvae cause little damage; control is unnecessary. In a few cases, however, the larvae can form a nuisance; control by spraying away the larvae on the underside of the leaves with a strong jet of water.
Provide a bird-friendly environment: birds eat insects including the larvae of the turnip sawfly. Letting go of a bunch of chickens between the strawberries now and then also helps.