Sawfly, common name applied to four-winged insects, widely distributed in temperate countries. Female sawflies have ovipositors, or egg-laying organs, that are partially modified into sharp-toothed, sawlike instruments with which the insect incises leaves and plant stems to form a receptacle for eggs. Female sawflies do much damage to plants; greater damage is done by the voracious larvae, which are capable of completely stripping a plant of its leaves. The larvae, commonly but erroneously called slugs, somewhat resemble butterfly caterpillars, differing in having a single simple eye (ocellus) on each side of the head, in lacking sharp hooklets on the legs, and in usually being coated with slime. When feeding on leaves, they assume a characteristic position in which the posterior end of the body is not in contact with the leaf but is coiled downward, hanging in space. When disturbed, some larvae eject a fluid from the head region. Most larvae pupate underground inside a cocoon.
Among the well-known American sawflies is the rose slug, which feeds on the leaves of rosebushes. The currant sawfly has spread to the United States from its native Europe; its larvae destroy currant bushes. The larch sawfly deposits its eggs in the leaves of larch trees, which the larvae defoliate. The largest of the common sawflies is about 2.5 cm (about 1 in) and has a wingspread of about 5 cm (about 2 in); the larvae of this species feed on the leaves of many trees, especially of willow.
Scientific classification: Sawflies belong to the order Hymenoptera. The rose slug is classified as Cladius isomerus, the currant sawfly as Nematus ribesii, and the larch sawfly as Pristiphora erichsonii. The largest of the common sawflies is classified as Cimbex americana.