Sawflies are a group of insects often encountered in gardens and natural areas, yet they remain widely misunderstood. This fascinating group holds a distinctive place within the insect world, differing from what their name might suggest. Understanding these insects offers insights into the intricate web of life.
What Distinguishes Sawflies?
Sawflies are not true flies (Order Diptera) despite their common name. They belong to the Order Hymenoptera, making them relatives of bees, wasps, and ants, specifically within the suborder Symphyta. Unlike most other Hymenoptera, sawflies have a broad attachment of the abdomen to the thorax, lacking the constricted “wasp waist.” Their name comes from the saw-like ovipositor adult females use to cut into plant tissue, typically leaves or stems, to deposit eggs.
Identifying Sawflies
Identifying sawflies requires recognizing features in both adult and larval stages. Adult sawflies vary in coloration, sometimes mimicking bees or wasps, but consistently lack the constricted waist. They typically possess four wings, distinguishing them from true flies, which only have two. Sawfly larvae are often mistaken for caterpillars. A reliable way to differentiate them is by examining their prolegs, which are fleshy, leg-like appendages on the abdomen. Sawfly larvae typically have six or more pairs of prolegs, unlike caterpillars (usually five or fewer), and lack the tiny hooks called crochets. Their resting postures can also be a clue, as many larvae coil into an S-shape or rear up when disturbed.
The Sawfly Life Cycle and Feeding Habits
Sawflies undergo complete metamorphosis: egg, larva, pupa, and adult. Females use their specialized ovipositor to insert eggs into plant tissue, often within leaves, needles, or stems. The larval stage is the primary feeding period, where these insects consume plant material. Many species are host-specific, feeding on particular types of plants like trees, shrubs, or grasses.
Larval feeding causes noticeable damage, from defoliation (entire leaves consumed) to skeletonization (only leaf veins remain). Some species bore into stems or create mines within leaves, feeding internally. After feeding, larvae typically enter a pupal stage, often in soil or within cocoons attached to plants or leaf litter. Adults then emerge, with a relatively short lifespan primarily focused on reproduction.
Ecological Role and Management
Sawflies fulfill several roles within ecosystems. Their larvae serve as a food source for various animals, including birds and other predators. While not widely recognized as pollinators, some adult sawflies visit flowers and contribute to plant pollination. However, some species become pests, causing damage to trees, shrubs, and garden plants, especially during their larval stage.
Managing sawfly populations involves several approaches. For smaller infestations, manually removing larvae or dislodging them with a strong jet of water can be effective. Promoting natural predators, such as insectivorous birds and parasitic wasps, helps regulate sawfly numbers. In cases of significant damage, various insecticides are available, but specific identification of the larvae is important, as treatments effective against caterpillars may not work on sawflies.