Sawfly larvae
Also known as Sawflies, Gooseberry sawfly
In short
Sawfly larvae look like caterpillars but belong to the same insect order as bees, wasps and ants. They often feed in groups and can strip the leaves from a shrub within days, and because they are not caterpillars, Bt sprays do not affect them.
How it looks
Caterpillar-like larvae, usually 1–2.5 cm long when fully grown, commonly pale green, sometimes with many black spots (as in gooseberry sawfly). The reliable test is the legs: sawfly larvae have six or more pairs of fleshy abdominal prolegs without hooks, while caterpillars have five pairs or fewer. They also have a single simple eye on each side of the head and a smooth head. Many feed side by side along leaf edges. Adults are small, wasp-like insects; they belong to the same order (Hymenoptera) as bees, wasps and ants.
Signs
Leaves eaten from the edges inward, sometimes down to the midrib; rapid defoliation of a single plant; clusters of larvae along leaf margins.
Life cycle
Females lay eggs into or on leaves; the larvae feed for a few weeks, then drop to the soil to pupate. Some species have one generation a year, others three or four in a season (e.g. common gooseberry sawfly).
What favours it
Outdoor shrubs and garden plants such as gooseberries and currants; eggs are laid on leaf undersides low in the bush, so larvae often start low in the centre of a bush and are missed until damage is heavy.
Prevention
- Check susceptible plants regularly from spring, including the centre of bushes and leaf undersides.
- Encourage birds, predatory wasps and beetles.
Treatment
Start with the first step and move down only if the problem persists.
- Pick off larvae by hand as soon as they are seen.
- Tolerate damage where you can; plants usually survive complete defoliation, although the next year's crop may be affected.
- If still needed, a contact insecticide labelled for sawflies — follow the product label. Do not rely on Bacillus thuringiensis (Btk): it only kills moth and butterfly caterpillars.
Pros and cons
Cons
- Can defoliate a shrub quickly.
- Easily mistaken for caterpillars, leading to the wrong treatment.
Look-alikes
- Caterpillars
- Five or fewer pairs of prolegs with tiny hooks, six eyes per side and a Y-shaped head suture; Btk works on them.
Affected plants
Gooseberries and currants are classic hosts; other sawfly species attack other shrubs, trees and perennials, and each species is usually specific to one plant group.
Related
Sources
- Is it a Sawfly Larva or a Caterpillar? — Ohio State BYGL
- Caterpillar — Wikipedia
- Gooseberry sawfly — RHS
Written in our own words from these sources. Check a product label before using any treatment.