How to recognise it
The larvae (which do the damage) are yellow/green, caterpillar-like creatures up to 15mm long with orange heads. The adults, which you rarely spot, are up to 1cm long with two pairs of wings, resembling flying ants.
Females lay eggs on the edge of leaves in May/June, which hatch a week later. The larvae feed on the leaf for about 4 weeks then move into the soil to pupate. They emerge from pupation in July/August as adults to lay eggs, which again hatch about a week later. This second generation overwinter in cocoons in the soil before pupating in early spring and emerging as adults in May/June.
Most of the reproduction is parthenogenetic as the vast majority of the sawflies are females; males are very rare.
Why it’s a problem
The larvae eat the surface of the leaf, generally on one side only, exposing the leaf veins. The damaged leaves look unsightly, but no long term negative effects are likely.
The adults mainly feed on pollen, so they aren’t a problem in the garden.
Where you are likely to find it
On roses between May and September.
How to deter it
Regular winter digging will expose any overwintering larvae and kill them (by exposure to the weather and predators).
How to get rid of it
The larvae can normally be removed by hand and destroyed, or sprayed off with a hose. If you wish to use a chemical control then most contact insecticides are effective against the larvae; repeat the treatment about a week after the first spraying if any larvae remain.
Is it good for anything?!