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Sawflies are winged insects which are members of the primitive group Symphyta, within the order Hymenoptera. They belong to a large group of insects with around 10,000 species which also include bees, wasps and ants. Although they are named as flies, they are more closely related to wasps than flies, even though they don’t sting.

What do sawflies look like?

There are many species of sawfly, and most look different to one another. Some can be easily mistaken for wasps or hoverflies, while others look like mosquitos. For example, conifer sawflies are almost always all black, while the gooseberry sawfly has black wings and yellowy orange legs and body.

Nonetheless, fully grown sawflies are usually around 15 millimetres. Their bodies are generally flat (planar) with a large head (cephalic portion), legs that end in hooked claws, and two pairs of wings that do not touch.

The most common colour for an adult sawfly is black, although orange and white varieties also exist. Adult sawflies generally have two wings but can have between two and four.

The caterpillar-like larvae are often brown, but they can vary in colour: some have orange or yellow heads, while others have black, brown, or olive heads. Nymphs (young larvae) are usually not as big as their parents, though they may be more colourful than the adults.

White banded rose sawfly, Allantus cinstus
White banded rose sawfly

How big are sawflies?

Sawflies vary in length depending on the species. They can measure anywhere between 2.5 to 20 millimetres. The largest sawfly on record was measured at 55 mm.

Sawfly larvae are large and caterpillar-like. They can grow up to 3 inches long and change colour as they age.

Large rose sawfly caterpillar eating rose leaves
Large rose sawfly caterpillar eating rose leaves

Where do sawflies live?

Sawflies are found in broad-leaved trees of the temperate regions of the world. The most common species are found on oak trees in Europe, North America and Japan. They can also be found in forests in Africa and other parts of the southern hemisphere but are absent in New Zealand and are very few in Australia.

Sawflies appear to thrive best at higher altitudes: sawfly populations are very high on Mt. Fuji, Japan.

In England, there are about 500 different species of sawfly, but this figure frequently changes as some new species are discovered, and others disappear.

How long do sawflies live?

Most sawfly species have short lives. Sawfly larvae feed and breed in the bark or cambium layer of a tree or shrub, and then they emerge to pupate into adults at the end of the year.

The average period of time between an egg being laid and the adult emerging is about 5 months. Adults are active for about 1-2 weeks before they die. This means that a sawfly’s lifecycle can last about six months, from hatching from an egg to death as an adult.

Arge pagana sitting on a green leaf in the garden

How do sawflies eat?

Sawfly caterpillars have hardened mouthparts that are shaped like a large drill bit. These mouthparts are also called mandibles, and they pierce the host plant’s bark tunnels to feed on the sap beneath the tree’s dry outer bark. The tree responds to this invasion by producing limonin, a chemical in its sap that is toxic to most small insects. Sawfly larvae have evolved an enzyme called peroxidase that helps them digest this toxic substance and allows them to thrive in trees.

The larvae of several sawfly species love to eat garden plants, and can demolish the foliage of medium-sized plants overnight.

Sawfly on green leaf
Sawfly on green leaf in the wild

Are sawflies good or bad?

Sawflies, like all insects, play a role in the food web of most ecosystems. Their feeding habits help control populations of other herbivorous insects, and they are themselves eaten by birds and rodents.

Sawflies are also important pollinating insects. In many areas of the world, sawflies are important pollinators of oak trees. Sawfly larvae carry pollen from one flower to another, spreading it to other flowers in search of more food. This helps ensure that flowers get pollinated, and more seeds are produced for future generations of plants.

However, for gardeners in some areas, many different species of sawfly are considered a serious pest. They will often feast on all the leaves from susceptible plants overnight, and that’s if it’s a light infestation. Rose bushes are particularly favoured, especially by the rose leaf rolling sawfly. Luckily they have many predators and natural enemies, such as beetles and wasps.

Sawfly caterpillars eating a rose bush
Sawfly caterpillars eating a rose bush

How do you get rid of sawflies?

Sawfly caterpillars are destructive to fruit trees and other plant buds. Unfortunately, there is not much that can be done about this. Though it’s difficult to control sawflies, it may be possible to protect fruit by covering it with netting during the time when the adult sawflies are active.

Chemical control may also be required if infestations are serious. Insecticides aren’t the answer to everything but can certainly help in serious cases. In general, it’s better to plant trees that don’t attract many sawflies.

Sources and References

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