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What Are Sawflies?

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An argid sawfly.

An argid sawfly.

Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

Sawflies don't have much of an identity of their own. As adults, they resemble flies or wasps, and when immature they look much like caterpillars. There's no single neat and tidy taxonomic group to which all sawflies belong. Unless you're an insect enthusiast or perhaps, a gardener, you probably wouldn't know a sawfly if it landed on you.

So what is a sawfly, exactly? They're often described as stingless wasps. They get their common name from the female's ovipositor, which unfolds like a jackknife. It functions like a saw blade, allowing her to cut into stems or foliage and deposit her eggs. People unfamiliar with sawflies may mistake this feature for a stinger, but there's no cause for concern. Sawflies are harmless to people and pets.

Sawflies look somewhat like flies, but a closer look will reveal four wings, not the single pair that is characteristic of the order Diptera. Some sawflies mimic bees or wasps, and in fact, they're related to both. Sawflies belong to the order Hymenoptera. Entomologists have traditionally grouped sawflies, horntails, and wood wasps in their own suborder, Symphyta.

Gardeners most often encounter sawflies as larvae, when they feed gregariously on host plants. At first glance, you might think you've got a caterpillar problem, but sawflies have behavioral and morphological differences that differentiate them from Lepidopteran larvae. If the larvae are all feeding along the leaf margins, and rear up their hind ends when disturbed, those are good signs that your pests are sawflies. Keep in mind that pest control products labeled for caterpillars, such as Bt, will not work on sawfly larvae.

Many sawflies are specialist feeders. The willow sawfly, for example, defoliates willows, while several kinds of pine sawflies focus their feeding on pines. The table below lists some of the more common North American sawflies that might present problems in the garden or landscape, and their host plants.

Within the 9 families of sawflies, we find some with unusual habits. Some xyelid sawflies oviposit their eggs inside the buds or cones of pine and fir trees. Cephid sawflies live within the stems of grasses or inside twigs. Certain tenethredinids are gall makers. And perhaps the oddest sawflies of all belong to the family Pamphiliidae. These crafty sawflies spin silk webs, or use their silk-producing glands to fold leaves together into well-camouflaged shelters.

Sources:

Common Sawfly Species in North America

Common NameScientific NamePreferred Host Plants
black-headed ash sawflyTethida bardaash
columbine sawflyPristiphora aquilegiacolumbine
currant sawflyNematus ribesiigooseberry, currant
dogwood sawflyMacremphytus tarsatusdogwood
dusky birch sawflyCroesus latitarsusbirch
elm sawflyCimbex Americanaelm, willow
European pine sawflyNeodiprion sertiferpine
introduced pine sawflyDiprion similispine, especially white pine
mountain ash sawflyPristiphora geniculatamountain ash
pear slugCaliroa cerasipear, plum, cherry, cotoneaster, hawthorn, mountain ash
red-headed pine sawflyNeodiprion leconteipine, especially red and jack pine
rose slug sawfly Endelomyia aethiopsrose
white pine sawflyNeodiprion pinetumeastern white pine
willow sawflyNematus ventraliswillow, poplar
yellow-headed spruce sawflyPikonema alaskensisspruce, especially white, black, and blue spruce
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