Sawflies, Horntails, and Wood Wasps

Families in the Suborder Symphyta

The sawflies, horntails, and wood wasps have traditionally been grouped together in the suborder Symphyta, as you will find in many entomology textbooks and references. The classification of the order Hymenoptera (ants, bees, wasps, and sawflies) is changing, however, particularly at the higher levels of the taxonomic order. For now, I've chosen to keep the sawflies, horntails, and wood wasps as a subgroup of the order.

This article offers brief descriptions of the 12 families that make up the subgroup known as symphytes.

Family Xyelidae - Pine Catkin Sawflies

Balsam shoot-boring sawfly.
Balsam shoot-boring sawfly. Ronald S. Kelley, Vermont Department of Forests, Parks and Recreation, Bugwood.org
The xyelid sawfly family, sometimes referred to as pine catkin sawflies, lives in close association with pines and other trees. This group is fairly small, with about two dozen species known in North America. Xyelid sawflies rarely measure more than 10 mm in length. Your best chance to find xyelid adults is in the early spring, when they feed on the catkins of birch and willow trees. Depending on the genus, xyelid larvae feed on male pine cones, buds and shoots of fir trees, or on hickory and elm.

Family Pamphiliidae - Leaf-Rolling and Webspinning Sawflies

Web-spinning pine sawfly.
Web-spinning pine sawfly. Fabio Stergulc, Università di Udine, Bugwood.org
It's somewhat uncommon to find a pamphiliid sawfly in North America, although roughly 75 species live here. The adults measure up to 15 mm long, but most are shorter. Some species are referred to as webspinning sawflies because the larvae live gregariously in nests, either made of silk entirely or built by attaching leaves together with silk. The solitary larvae make shelters by rolling up leaves, much like some caterpillars do. As a group, pamphiliids feed on a variety of host plants, with some preferring coniferous trees and others choosing deciduous hosts.

Family Pergidae - Pergid Sawflies

Leaf-feeding sawfly.
Leaf-feeding sawfly. Stephen D. Hight, USDA Agricultural Research Service, Bugwood.org

Pergid sawflies make up a small but diverse family found primarily in the neotropics. Most of the 400-plus species inhabit Australia and South America. Less than 10 species are known from North America, and all of these belong to a single genus, Acordulecera. Pergid sawfly species are often sexually dimorphic. Compared to other sawflies, they have reduced wing venation. Pergidae larvae are sometimes called spitfires. Their feeding habits are largely undocumented, although known species feed on a variety of host plants, from oaks and hickories to aquatic ferns or leaf litter.

Family Argidae - Argid Sawflies

An argid sawfly.
An argid sawfly. Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
Most argid sawflies are dark in color, with stout bodies. Though most inhabit the tropics, we find about 70 species in North America, the bulk of them living in the southwest. Argids range from 8-15 mm in length. They're easily differentiated from other sawflies by their unique antennae. The terminal segment (the third segment of just three) is elongated, and in males is sometimes shaped like a U or Y. As a family, argid larvae vary quite a bit in what they eat. Individual species often specialize on a host plant. Arge humeralis, for example, feeds on poison ivy.

Family Cimbicidae - Cimbicid Sawflies

On the larger side of the family, the cimbicid sawflies range in length from 15-25 mm. Cimbicids have bulky bodies and slightly clubbed antennae. Many resemble bees. The thorax and abdomen fuse together broadly, without a waist (as you would find in wasps). Though we have just a dozen species in North America, they include some of our most familiar sawflies, like the elm sawfly.

Family Diprionidae - Conifer Sawflies

European pine sawfly.
European pine sawfly. Louis-Michel Nageleisen, Département de la Santé des Forêts, Bugwood.org

As you might predict from their common name, larvae of the conifer sawflies feed on conifers. Some cause enough damage to be considered pests, particularly in our northern forests. As adults, conifer sawflies are small (6-12 mm in length). Their antennae have at least 13 segments. In females, the antennae are serrate in form, while in males they can be either pectinate or bipectinate. Just under 50 species of conifer sawflies inhabit North America. There are about 140 species of diprionids known worldwide.

Family Tenthredinidae - Common Sawflies

Elm leafminer.
Elm leafminer. Whitney Cranshaw, Colorado State University, Bugwood.org

If you find a sawfly, there's a 90% chance it belongs to the family Tenethredinidae – that's why they're called common sawflies! Common or true sawflies usually mimic wasps, though they can't sting. You'll often find these brightly colored sawflies among flowers. Sawflies in this family range in size from small (as short as 5 mm) to medium (up to 20 mm long). Some tenethredinids are believed to be important pollinators, many prey on other insects as adults, and a few are gallmakers. About 800 species of common sawflies inhabit North America.

Family Cephidae - Stem Sawflies

Rose stem sawfly.
Rose stem sawfly. Whitney Cranshaw, Colorado State University, Bugwood.org
Though only 13 species of stem sawflies live north of Mexico, a few of them can be serious pests of certain crops. The wheat stem sawfly, for example, causes millions of dollars in damage to wheat crops in the northern plains region each year. The larvae of stem sawflies bore into the stems of grasses, canes, and sometimes twigs. Adult stem sawflies have slender, cylindrical bodies, with an elongated pronotum and clubbed antennae. They can often be found around yellow flowers.

Family Anaxyelidae - Incense-Cedar Wood Wasps

If you want to collect an incense-cedar wood wasp, you'll need to go to northern California or Oregon. We have just one species from this family in North America, Syntexis libocedrii, and it lives only in one small area of the U.S. Narrow your search to areas near its two host trees – incense cedar or Douglas fir trees. The female Syntexis libocedrii usually oviposits her eggs on trees weakened by disease or fire.

Family Siricidae - Horntails

Sirex noctillo.
Sirex noctillo. David R. Lance, USDA APHIS PPQ, Bugwood.org
Horntails look menacing, thanks to a spear-like projection on their hind ends that most people assume to be a stinger. Rest assured, horntails are harmless, and that horn isn't going to hurt you. Females also have a long ovipositor used to drill into a host tree and insert her eggs. The larvae are wood borers of either conifers or hardwoods, depending on the horntail species. Horntail adults measure 25 mm or more in length, making them some of the largest symphytes around. There are about 100 horntail species worldwide, with a quarter of them living in North America. Most of the North American species live in the east.

Family Xiphydriidae - Wood Wasps

Xiphydria longicolli.
Xiphydria longicolli. Fabio Stergulc, Università di Udine, Bugwood.org
If you're looking for insects for your collection, wood wasps might be tough to find. They're not very common in North America, where just 11 species live. Wood wasps look similar to horntails, but tend to be much smaller (5-23 mm in length). Wood wasp larvae bore into smaller dead wood, such as twigs and branches, rather than into the trunk of their host trees. They only use deciduous trees for hosts.

Family Orussidae - Parasitic Wood Wasps

Parasitic wood wasps probably don't belong on this list, as taxonomists now believe they are closer relatives to the Apocrita than to the Symphata. Until consensus (or something approaching consensus) is reached on this matter, I'll leave them in this group, since any references you're using today probably list them with the sawflies and horntails. The parasitic wood wasps are rare finds, and just 9 species live in North America. Not much is known about the orussids yet, but their larvae are thought to parasitize wood-boring beetles. The adults resemble horntails, though they are considerably smaller at just 8-14 mm in length.
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Hadley, Debbie. "Sawflies, Horntails, and Wood Wasps." ThoughtCo, Mar. 3, 2017, thoughtco.com/sawflies-horntails-and-wood-wasps-1968110. Hadley, Debbie. (2017, March 3). Sawflies, Horntails, and Wood Wasps. Retrieved from https://www.thoughtco.com/sawflies-horntails-and-wood-wasps-1968110 Hadley, Debbie. "Sawflies, Horntails, and Wood Wasps." ThoughtCo. https://www.thoughtco.com/sawflies-horntails-and-wood-wasps-1968110 (accessed January 22, 2018).