Sawflies are a large and diverse group of insects that belong to the order Hymenoptera, along with bees, wasps , and ants. Their name comes from the saw-like part of the insect used for cutting into plant material in order to lay eggs.
Sawflies undergo complete metamorphosis through their life cycle, from egg to larvae, pupae, and winged adult. Eggs hatch into caterpillar-like larvae, which eat the fruit or leaves of their host plant, and it is this stage that can be an issue for gardeners, although the damage they cause is mainly cosmetic. Many sawflies feed on a specific plant species or plant family and are therefore relatively easy to identify, usually by the telltale damage they cause.
How to identify sawflies
Apple sawfly larvae live in young, developing apples, tunnelling under the skin and into the core. The fruit falls early, in summer, from where the larvae tunnel out and into the soil to continue their life cycle. Affected fruit that stays on the tree has ribbon-like scars and is often misshapen.
The creamy-white, black-spotted and blotched larvae with orange, with black heads, eat the leaves of berberis and mahonia. First recorded in the UK in 2000, it has now spread through most of England and into Wales.
The pale green larvae may partly or completely strip a gooseberry bush of leaves, in spring or summer. Currant bushes may also be affected.
Rose leaf rolling sawfly
The name ‘rose leaf rolling sawfly’ comes from this sawfly’s habit of injecting a chemical into young rose leaves, which causes them to curl protectively around her eggs. In mid-summer, the young rose leaves curl up overnight, and after a week small green caterpillars hatch and start to strip the leaves, leaving behind skeletonised foliage.
Solomon’s seal sawfly
Soloman’s seal larvae are greyish white with black-heads, and can rapidly strip the foliage from entire plants of the genus Polygonatum, in early summer.
The larvae of geranium sawfly (Ametastegia carpini) look like tiny grey caterpillars, around 12mm long. They munch holes in the leaves, leaving an unsightly, lace-like appearance.
Is sawfly a problem?
Although leaf-eating sawflies can cause unsightly damage to plants and fruit, plant health generally is usually unaffected. Apple sawfly usually only attacks a proportion of the fruit and therefore rarely significantly affects the harvest. Established roses survive attack and gooseberries seem to cope well with an infestation, with the leaves simply growing back after the larvae have moved on.
Other plants that may be affected by sawfly include aquilegia, geum and pine.
How to combat sawflies without chemicals
There’s no real need to combat sawflies. Plants withstand attack without suffering, and there are usually plenty of apples to go around, despite the attempts of sawfly larvae. What’s more, using chemicals kills beneficial insects such as bees and butterflies, as well as sawflies.
Employing these organic techniques may be necessary in some circumstances, otherwise just let nature take its course:
- Cultivation – larvae of many sawflies overwinter in the soil under their host plant, so cultivating the ground beneath susceptible plants by clearing debris and lightly raking the soil, will expose the larvae to be killed by frost, and to be eaten by birds and other predators
- Hand picking – remove affected fallen apples, rather than leaving them lying on the ground, to stop the larvae escaping into the soil and pupating. Pick off and bin rolled-up rose leaves to prevent the larvae maturing, although with large numbers of leaves, they are best left or the rose will suffer
- Hand-squashing – inspecting the leaf undersides of susceptible plants in spring and early summer can reveal clusters of eggs, or young larvae. Leaves may be scarred where eggs have been laid. Intervening early and squashing with finger and thumb can prevent a large infestation
- Encourage natural predators – it’s far more interesting to see which natural predators control your sawfly than to control them yourself. Look out for birds, wasps and even ground beetles feasting on sawfly larvae, which they could be taking back to feed their young