Sawfly — Sawflies make up the suborder Symphyta, a group of largely phytophagous insects in the order Hymenoptera. This group is an artificial assemblage of superfamilies (the overall group is paraphyletic), but the name is still in common use, and treated as a suborder, though it seems likely it will be phased out in future classifications. These superfamilies are regarded as the most primitive taxa within the Hymenoptera (some going back 200 million years), and one of the taxa within the Symphyta gave rise to the suborder Apocrita (wasps, bees and ants – this group is considered monophyletic). In the opinion of many experts, the most likely sister taxon to the Apocrita is the family Orussidae, the only Symphytan group which is parasitic.
Sawflies are distinguishable from most other Hymenoptera by the broad connection between the abdomen and the thorax , and the caterpillar-like larvae. The common name comes from the appearance of the ovipositor, which looks much like the blade of a saw. This ovipositor, which is modified into a “sting” in some members of the Apocrita, is not used as a weapon. Females use the ovipositor to cut into plants where they lay their eggs. A few species have long thin ovipositors used to drill holes deep into wood. Large populations can cause economic damage in cultivated areas and forests.
The larvae look like caterpillars (the larvae of moths and butterflies), with two notable exceptions; (1) they have five or more prolegs on the abdomen (caterpillars have five or fewer), and (2) they have two ocelli instead of the caterpillar’s six. Typical sawfly larvae are herbivorous, the group feeding on a wide range of plants. Individual species, however, are often quite specific in their choice of plants used for food. The larvae of various species exhibit leaf-mining, leaf “rolling”, or gall formation. Three families are strictly xylophagous, and called “wood wasps”, and one family is parasitic. The larvae that do not feed externally on plants are grub-like, without prolegs.
Adult sawflies, except for those in the family Cephidae, have structures that latch onto the underside of the forewings to help hold the wings in place when the insect is at rest. These “cenchri”, which are absent in the suborder Apocrita, are located behind the scutellum on the thorax. Adults of some species are carnivorous, eating other insects, but many also feed on nectar.