The sawfly is an insect often confused with a flying ant, a small moth, or a wasp, yet it belongs to its own distinct group. Classified within the order Hymenoptera, the same group as bees, wasps, and ants, sawflies are part of the suborder Symphyta. Adult sawflies are harmless because they do not possess a stinger, despite their close relation to stinging insects. They feed on plants, and their presence is most often noticed by the damage their young cause in gardens and forests.
How to Identify a Sawfly
The most defining feature distinguishing an adult sawfly from a true wasp or bee is the absence of the constricted “wasp waist.” In sawflies, the abdomen joins the thorax broadly, creating a stout, continuous body shape. This morphological difference results in a body shape that looks more like that of a common fly than the narrow, pinched connection seen in other Hymenoptera.
Sawflies possess two pairs of membranous wings, a feature they share with wasps and bees. Their antennae offer a reliable identification clue, as they are typically thick, straight, and thread-like, unlike the elbowed or hooked antennae of many wasps. Coloration varies widely, ranging from dull black or brown to bright yellow-and-black patterns that mimic stinging insects for defensive purposes.
The Unique Function of the Saw-Like Ovipositor
The common name “sawfly” is derived directly from the female’s highly specialized egg-laying organ, the ovipositor. This organ is not a stinger but a complex biological cutting tool located at the tip of the abdomen. The ovipositor is composed of two interlocking, saw-like blades, called lancets, which are lined with tiny teeth.
The female uses these hardened, serrated blades to mechanically slice into plant tissue, such as a leaf, stem, or conifer needle. This action creates a protective pocket or slit within the plant where she safely deposits her eggs. The incision shields the eggs from predators and environmental threats, and the depth and location are specific to the sawfly species and their host plant.
Life Stages and Horticultural Impact
Sawflies undergo complete metamorphosis, progressing through four distinct stages: egg, larva, pupa, and adult. The larval stage is the one most frequently encountered and is responsible for nearly all the horticultural damage associated with this insect. Sawfly larvae are often mistaken for the caterpillars of moths or butterflies because they are soft-bodied and chew on plant leaves.
A reliable method for distinguishing a sawfly larva from a true caterpillar is to count the fleshy, leg-like appendages on the abdomen, known as prolegs. Sawfly larvae typically have six or more pairs of prolegs, which lack the tiny hooks found on caterpillars. In contrast, true caterpillars usually have five or fewer pairs of abdominal prolegs.
These larvae feed voraciously, causing several types of damage. This includes skeletonizing leaves by eating the tissue between the veins, or completely defoliating plants. Certain species feed gregariously in large groups, rapidly stripping needles from entire branches. Management can often be accomplished non-chemically by simply hand-picking the clusters of larvae off the foliage or by using a strong jet of water to dislodge them.