Larch Sawfly

How to identify it

• Grown larvae have shiny jet-black heads and bodies that are gray-green on the back and whitish underneath; UMN gives about 16 mm.^[1][2]
• New shoots curl where females have laid rows of eggs under the bark, and the curl stays visible for several years.^[1][2]
• Adult females are black with a broad orange band on the abdomen.^[1]

Where it lives

Reported in North America since 1880 near Boston and now found from Maine to Washington and in Alaska, south to Maryland and West Virginia.^[1]

Biology and life cycle

Larvae overwinter as prepupae in tough brown cocoons in the duff; adults emerge from mid-May into June, nearly all of them females that reproduce without mating.^[1][2]

Each female lays 20 to 200 eggs in the new terminal twigs; larvae hatch in early June and feed in colonies on the older needles for about three weeks.^[1][2]

Because adults emerge over about six weeks, all larval stages can be on a tree at once, and feeding can run into September; there is one generation a year.^[1][2]

Damage and signs

• Hosts are tamarack, western and subalpine larch and planted European, Japanese and other larches.^[1][2]
• Larvae eat needles on the older parts of twigs and can strip a tree, but complete defoliation is rare because they skip the new shoots.^[1][2]
• Larches refoliate and survive many years of defoliation, though growth nearly stops; small trees can die after a few heavy years, and tamarack on thin bog soils after about 7.^[1][2]

Health risk

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

Control

Biological control

Small mammals eat many larvae in bogs, and parasitoid wasps, including strains and species released from Europe, help suppress outbreaks.^[1]

Pesticides

UMN suggests checking larches in early summer and treating larvae only if needed; the 1971 Forest Service leaflet notes overlapping broods can require two applications.^[1][2]

Related profiles

• Larch Casebearer
• Pine Sawflies
• Yellowheaded Spruce Sawfly

Common questions

Why are the new shoots on my larch curled?

Egg laying by the larch sawfly makes new twigs curl; look for rows of egg slits and feeding larvae behind the curl.^[1][2]

Will larch sawfly kill my tamarack?

Rarely; larches survive years of defoliation, though growth slows to a standstill.^[1][2]

Sources

1. USDA Forest Service (Forest Insect & Disease Leaflets), “Larch Sawfly (Forest Pest Leaflet 8, revised March 1971).” www.fs.usda.gov/foresthealth/docs/fidls/FIDL-08-LarchSawfly.pdf (accessed 2026-10-16)
2. University of Minnesota Extension, “Sawflies (Yard and Garden Insects).” extension.umn.edu/yard-and-garden-insects/sawflies (accessed 2026-10-16)
3. iNaturalist, “Pristiphora erichsonii taxon page (order and family).” www.inaturalist.org/taxa/454773 (accessed 2026-10-06)