Pest profile

Elm Sawfly

Cimbex americana (also spelled Cimbex americanus) · Hymenoptera: Cimbicidae[3]

The elm sawfly is one of North America's largest sawflies: a metallic blue, non-stinging wasp relative whose large, wrinkly, yellowish-white larvae feed on elm and willow leaves.[1][2]

Elm sawfly larva on wet pavement, yellowish white with a dark stripe down its back
Elm sawfly larva on wet pavement, yellowish white with a dark stripe down its back. (c) Allison Zon, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Adults are about an inch long, deep metallic blue, with smoky translucent wings and orange, knobbed antennae; females have yellow spots along the sides of the abdomen.[1][2]
  • Larvae grow to about 2 1/4 inches, yellowish white and wrinkled, with a dark stripe down the back.[1][2]
  • Like other sawfly larvae, they have more pairs of prolegs than moth caterpillars.[1]

Look-alikes

Look-alikeHow to tell them apart
Northern giant hornetIowa State lists the elm sawfly among the native insects mistaken for the giant hornet; the sawfly is only about an inch long and can't sting.[2]
Cicada killerOur largest wasp, 1 1/4 to 1 5/8 inches long, black with pale yellow stripes and spots and translucent orange wings.[2]

Where it lives

It has defoliated willow and elm in the northern Great Plains and the Midwest, while NC State calls it uncommon in North Carolina.[1][2]

US map: public records from 48 states since 1990 (GBIF).

Biology and life cycle

Adults emerge from late May through June; females saw pockets in elm leaves and lay up to 12 eggs per leaf, 30 to 150 eggs in all.[1]

Larvae feed for about a month, then spin tough, papery cocoons about 1 inch long in leaf litter or just under the soil.[1]

Some spend two or more winters in the cocoon, so there is one generation a year or every two to three years.[1]

Damage and signs

  • Larvae feed on leaves of elm and willow, also maple and basswood, and have been reported on alder, apple, birch, boxelder and poplar.[1][2]
  • Adults chew bark of twigs for sap; in the Midwest and north the species has caused serious defoliation and tip dieback of windbreak and street trees.[1]

Health risk

None; sawflies don't sting and are harmless.[2]

Control

Prevention

Monitor susceptible trees for larvae from late June to August.[2]

Biological control

Eggs and larvae are parasitized by wasps and flies, and shrews and deer mice eat the larvae in their cocoons.[1]

Pesticides

Sawflies are sensitive to insecticides; products labeled for leaf-feeding pests of elm should give adequate control.[1]

Common questions

What is the big blue wasp on my elm?
Probably an adult elm sawfly, a non-stinging relative of wasps about an inch long.[1][2]
Is the elm sawfly a giant hornet?
No. It is much smaller, metallic blue and can't sting.[2]
What is the big yellow caterpillar curled on elm leaves?
Likely an elm sawfly larva, up to 2 1/4 inches long with a dark stripe down the back.[1][2]

Sources

  1. NC State Extension, “Elm Sawfly (PDIC Factsheet).” content.ces.ncsu.edu/elm-sawfly (accessed 2026-10-15)
  2. Iowa State University Extension and Outreach, “Elm Sawfly and other Asian Giant Hornet Look-Alikes (Yard and Garden, June 2020).” yardandgarden.extension.iastate.edu/article/2020/06/elm-sawfly-and-other-asian-giant-hornet-look-alikes (accessed 2026-10-15)
  3. iNaturalist, “Cimbex americanus taxon page (order and family).” www.inaturalist.org/taxa/1028452 (accessed 2026-10-06)

Updated 2026-10-15. Built from sourced records. Spot an error? Tell us.