Introduction to Sawflies

Sawflies are a group of insects whose larval stages feed on the leaves of plants This is wide group that includes many species, each of whom prefer different plants. Sawflies get their common name from the saw-like appearance of their ovipositors; which females use to cut into leaves to lay eggs. There are about 25 families and 8,000 species worldwide, though most of the species we are familiar with here in Wisconsin are phytophagus true sawflies.

Adult sawflies somewhat resemble wasps, but their mid-sections are wider and they do not sting. You will most often see them resting on leaves and occasionally flying for short periods of time. Adults typically only live for a few days to weeks, just long enough to lay eggs.

Sawflies are parthenogenetic, meaning they do not need to mate to reproduce. Thus, most sawflies are female, with some species not producing any males at all. Females use their saw-like ovipositors to cut into fresh leaves, petioles, or small stems and deposit their eggs. Depending on the species, some lay their eggs in the leaf veins, along the edges of leaves, or scattered across leaves. Some are deposited inside the leaf tissues, and some are glued to the surface. Eggs then hatch in two to eight weeks, depending on species and weather conditions. Most larvae resemble caterpillars, though they different. Both sawfly larvae and caterpillars have three pairs of thoracic legs but differ in that caterpillars have 2-5 pairs of prolegs (fleshy, leg-like projections) on the abdomen while sawflies have 6 or more. Caterpillars also have multiple pairs of eyes while sawfly larvae only have one. Sawfly larvae appear in groups and react to disturbances by rearing back, while caterpillars are typically found on their own. Because sawflies stay together and eat in groups, they can consume a lot of plant material quickly, doing noticeable damage. Sawfly larvae are a great food source for many species of birds, lizards, frogs, ants, and other predatory insects.

Sawfly larvae then undergo 6 instar stages, growing in size with each one. Typically, they are noticed during the later instars when the larvae are larger and consuming more plant material. After 2-4 months, they pupate either in the soil or by spinning a cocoon. Depending on the species, this may take a few to many months. Some species can produce multiple generations in a year, but most only produce one.

Some of the most common sawfly species that affect trees in our region are as follows.

European Pine Sawfly, Neodiprion sertifer, is found on Jack Pines, Mugo Pines, Scot’s Pine, Red Pine, and more. Larvae typically emerge in mid-May and adults lay eggs in the Fall, which overwinter. The larvae grow to an inch long, have green and gray stripes and a black head, and feed in groups on last year’s needles. They eat needles one branch at time and can even strip all needles from a tree.

Pear Sawfly, Caliroa cerasi, is a species native to Eurasia. It is most commonly found on Apple or Pear trees, but can also be found on other members of the rose family, such as Plums, Cherries, and Hawthorns. The larvae appear in early June, growing up to half an inch in length and are olive green.
They eat the leaves, leaving the veins behind. Heavily eaten leaves will drop prematurely, leaving the tree bare and stressed.

Birch leafminer, Fenusa pusilla, is a European species that mostly feeds on White, Gray, and Paper Birches. Yellow Birch and River Birch can be affected, but that is less common. Birch leafminer feed between the top and bottom layers of the leaves, creating blister-looking translucent spots on new leaves. The spots eventually turn brown and papery and the leaves drop off. Birch leafminer infestations rarely cause serious injury, and it is typically considered a cosmetic issue.

Elm Sawfly, Cimbex americana, is a species native to the United States that feeds primarily on Elm and Willow, though they will at times go after Cottonwood, Maple, Poplar, and Birch species. Larvae appear whitish, light gray, or yellow-ish and grow up to 1.5 inches. They have a black strip that runs down their body and rows of black dots along their sides. Infestations are localized to one tree or trees in close proximity. They take longer to reach their final instar, and thus any defoliation occurs later in the season, causing less stress on trees.

Dogwood Sawfly, Macremphytus tarsatus, is another native species which feeds on a variety of ornamental and native dogwood trees and shrubs. Larvae have black and yellow bars across their backs and solid yellow underbellies, though a white waxy coating they produce can make them appear whitish. They can defoliate Dogwoods quite quickly, and smaller trees and shrubs can undergo considerable stress as a result. They cocoon in rotten wood fibers and if they cannot find sufficient space, they may cocoon in siding of buildings, leading the woodpecker damage.

There are a few invasive species of sawflies that can cause more damage to our area, since their predators are not present here yet. For example, Elm Zigzag sawfly was detected in Wisconsin in Summer 2024 for the first time. They are named for the zigzag feeding pattern their larvae take, and they can produce multiple generations per year, spreading across the eastern part of the country quickly. Damage severity from this species can vary widely, and its spread is being closely monitored by the DNR. Redheaded Pine sawfly was also detected in the norther part of the state in 2019 and has been reappearing every year since.
For the most part, sawflies can only do so much damage to large mature trees. It is small, young, or sick trees that are more at risk of injury and death. Young trees that are defoliated can have their growth stunted, or if repeated defoliated, can be killed. Predators and parasitoids typically keep sawfly populations under control, although more severe infestations can potentially appear, which may require physical or chemical controls. If found in small numbers, sawfly larvae can be physically removed from plants and killed in soapy or boiling water. You may also consider insecticidal soap or neem oil for minor infestations. Keep in mind that Bt sprays will not work against sawfly larvae. For severe infestations of large trees, contact Tree Health Management for other chemical control options.