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Birch Sawfly

Arge pectoralis[3]

The birch sawfly is a native sawfly whose larvae feed along the edges of birch leaves in summer.[1][2]

Group
Insect
Order
Hymenoptera
Family
Argidae
US records
19 states
Sources
3 cited
Updated
2026-10-17
Birch sawfly larva with rows of black spots and an orange head on a leaf
Birch sawfly larva with rows of black spots and an orange head on a leaf. (c) Christian Back, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Related profiles
  9. Common questions
  10. Sources

How to identify it

  • Larvae are pale yellowish-green with rows of black spots and a dull orange to reddish-yellow head, about 0.75 to 1 inch long when grown.[1][2]
  • Feeding larvae often hold the end of the abdomen raised behind them.[1]
  • Adults are about 0.3 inch long with 3-segmented antennae.[2]

Look-alikes

Look-alikeHow to tell them apart
Dusky birch sawflyA related birch sawfly whose larvae feed in groups along leaf edges with similar damage.[1][2]

Where it lives

Found through Canada and parts of the northeastern United States.[1]

US map: public records from 19 states since 1990 (GBIF).

Biology and life cycle

Pupae overwinter in the leaf litter at the base of host trees, and adults emerge in June and July and lay eggs in rows along leaf edges.[1][2]

Larvae are active from about mid-June into September.[1]

Damage and signs

  • Birch is the main host; alder, hazelnut and willow are occasional hosts.[1][2]
  • Damage is usually localized, but occasional large populations cause considerable defoliation.[1][2]

Health risk

None to people or pets.[1][2]

Control

Traps and physical control

Watch for small larvae along leaf edges and prune out or crush them with a gloved hand.[1][2]

Biological control

Native natural enemies, including predatory stink bugs, usually keep numbers down, so it can usually be tolerated.[1][2]

Pesticides

Bacillus thuringiensis kurstaki will not work, because sawfly larvae are not caterpillars.[1]

Common questions

What are the spotted larvae eating my birch leaves in July?
Often birch sawfly larvae, which feed along the leaf edges.[1][2]
Should I spray birch sawflies?
Usually not; natural enemies keep them in check and the damage is usually local.[1][2]

Sources

  1. UMass Extension Landscape, Nursery and Urban Forestry Program (Landscape Insect & Mite Guide), “Arge pectoralis (Birch Sawfly).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/arge-pectoralis (accessed 2026-10-16)
  2. Pacific Northwest Insect Management Handbook (Oregon State, Washington State, University of Idaho), “Birch (Betula)-Sawfly (Hosts and Pests of Landscape Plants).” pnwhandbooks.org/insect/hort/landscape/hosts-pests-landscape-plants/birch-betula-sawfly (accessed 2026-10-16)
  3. iNaturalist, “Arge pectoralis taxon page (order and family).” www.inaturalist.org/taxa/202672 (accessed 2026-10-06)

Updated 2026-10-17. Built from sourced records. Spot an error? Tell us.