ADLib Glossary (S)

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Sawflies

A sawfly is an insect closely related to wasps, bees and ants. It has no sting but the females have a structure at the end of their abdomens (at their tail) which they can extend and which has, along one side, teeth just like on a carpenter's saw. The female uses this 'saw' to cut slots in plants, usually the stem, into which she lays her eggs.

Sawflies are usually considered to be the most primitive of the insect order Hymenoptera, which includes the bees, wasps, ants and parasitic wasps.

The sawflies form a complete suborder known as the Symphyta and are characterised by the absence of a 'wasp-waist' constriction between the thorax and the abdomen (in sawflies the thorax runs into the abdomen in almost a straight line). All sawflies have two-pairs of wings, as in most of the other Hymenoptera (apart from those that have no wings at all), but the venation of their wings is considered to be similar to the ancestral hymenoptera and is extremely variable with an individual sawfly often having differences in venation between the left and the right wings.

The larvae of all sawflies (at least in Britain) feed on plant material - and the majority feed openly on leaves. Some may feed singly when they are usually cryptically coloured as a means of camouflage) whilst others are distinctly gregarious when they are often brightly coloured and have group movements (e.g. body lashing) as a means of deterring predators and parasites. There is also some evidence that the larvae may produce chemical defence secretions as handling large numbers of Diprion larvae can cause skin irritation.

Most sawfly species are quite specific in terms of the host plant upon which they feed with very few being polyphagous. However, as a group sawflies feed on a large range of plant species ranging from primitive plants such as horsetails and ferns, through grasses and herbaceous plants to woody plants and trees such as conifers, fruit and other deciduous trees. However, the foodplants, habits and biology of several British sawflies are still unknown and much work remains to be done both on sawflies in general, but particularly with sawfly larvae.

The free living larvae of sawflies are very similar in appearance to the larvae (caterpillars) of the Lepidoptera (butterflies and moths) though they have only one pair of eyes rather than the several eye pairs found in lepidopterous larvae. Sawfly larvae have 6 or more pairs of abdominal pro-legs whilst lepidoptera never have more than 5 pairs. However, due to constraints brought on by specific habitat requirements those sawfly larvae which mine leaves or bore in stems and trunks may have the legs reduced in number and/or size and the larval morphology of these species may vary considerably from species to species.

Sawfly larvae provide valuable food for game birds.

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