Wood Wasps and Sawflies

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A photograph of a Greater Horntail (_Urocerus gigas_) laying eggs within wood using a long ovipositor that is often mistaken for a sting.

A Greater Horntail (Urocerus gigas) laying eggs within wood using a long ovipositor that is often mistaken for a sting. These impressive insects are completely harmless.
Photograph by Holger Gröschl licensed under Creative Commons.

The suborder Symphyta (Wood Wasps and Sawflies) includes those Hymenoptera which are structurally most primitive. There are approximately 500 species present in Britain.

Wood Wasps

Wood Wasps are so named because they feed on wood as larvae. Some look very impressive, such as the Greater Horntail (Urocerus gigas), due to their large size and a needle-like ovipositor projecting well beyond the apex of abdomen. Many people believe the long ovipositor is a sting, it is not and these insects are harmless. The larvae will tunnel and feed on the wood for up to 2 to 4 years, but if the wood is cut and dried the larval life may be prolonged 7 to 8 years.

One interesting story is that during the Crimean War the larvae of Sirex juvencus (Siricidae) were found chewing their way through lead bullets. The insects must have been living in the wooden boxes that the bullets were stored in.

Some Wood Wasps form a symbiotic relationship with certain fungi. The presence of the fungi in the wood is necessary for the insect's larval development, the fungus being spread from tree to tree by the female ovipositor.


Sawflies, as the name suggests, possess a saw-like ovipositor that has a sharp edge with teeth (or teeth upon teeth) to saw into leaves or trees to lay eggs. The second part of the name may be confusing as they are not true flies.

Most Sawfly larvae feed on leaves: some are leaf miners (living between the upper and lower surfaces of the leaf), a few make leaf rolls, and some cause galls like the Pontania species (Tenthredinidae) who are responsible for producing the pea or bean-shaped galls on leaves. Some oviposit into the base of flowers and the larvae feed in the developing fruit, which usually falls off when the larva is mature. Some are external feeders that skeletonise leaves. The larvae of Caliroa ceri (Tenthredinidae) are covered with slime and therefore appear very glossy. The Blasticotomidae, of which there is only one very rare species in Britain, bores into ferns, exuding a ball of froth.

The Cimbicidae are medium to large, dumpy species with antennae that end in a club. They may bite when handled - in fact the males of many species have enlarged hind legs and mandibles, which they use in fights with rival males. The male antennae of the Diprionidae are feathery to detect the sex pheromones of the females; in contrast, the female antennae are serrate to detect chemicals from conifers, the larval food plant. The larvae of sawflies differ from those of other Hymenoptera in having short, leg-like prolegs under the body, making them resemble butterfly or moth caterpillars.

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