How to recognise it
Cream-coloured eggs hatch into very small, lime green larvae with large black heads. These grow into larger, bright green/yellow larvae with distinctive stripes of black markings. The adult sawflies are 5 to 7.5mm long, dark-copper coloured flying insects with two pairs of wings.
The female uses her ‘ovipositor’ (a saw-like device from which the common name of ’sawfly’ is derived) to pierce a leaf and lay a batch of 50 to 80 cream-coloured eggs on it. The resulting larvae can be distinguished from caterpillars by having at least six pairs of fleshy prolegs (along their abdomen) whereas caterpillars have only 4 or 5 pairs. They feed then move into the soil to form pupa from which the adult sawflies emerge. Two or three generations can be produced each year.
Why it’s a problem
The larvae consume leaves. A severe sawfly attack can completely defoliate a tree.
Where you are likely to find it
Most common on willow shrubs and trees, although aspens may also be affected. The larvae are most prevalent over the summer months.
How to deter it
The sawflies overwinter in the soil, so winter digging around willows can expose them to the cold and kill them.
How to get rid of it
Where the infestation is isolated the affected parts can be removed and destroyed (not on your compost heap).
Is it good for anything?!
Other useful information
The acrobatic poses which the larvae often take are thought to be to ward off predators.