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Green larch looper

Green larch looper - Dorsal view of mature larva (green morph), on western larch
  • Latin name: Semiothisa sexmaculata (Packard)
  • French name: Arpenteuse verte du mélèze
  • Order: Lepidoptera
  • Family: Geometridae
  • Synonym(s): Macaria sexmaculata


Quebec, Newfoundland, Nova Scotia, Ontario, British Columbia

This species is distributed throughout the host range in the interior of British Columbia from the Yukon border south to the Okanagan and Columbia drainages; it also occurs from the Yukon to Newfoundland and Labrador, north to Fort McPherson, Northwest Territories, and south to Oregon and Massachusetts.



Damage, symptoms and biology

The larch looper is a common, frequently abundant and occasionally destructive solitary defoliator.

Mature larva up to 19 mm long. This species has two distinct colour morphs. The more common green morph has a green head and body; faint fine white addorsal lines; broader white subdorsal stripes bordered below by dark line; creamy yellow spiracular stripes. The brown morph has a light tan head with dark markings; the body is brown with a dark brown wishbone mark on the dorsum of each abdominal segment; broken white subdorsal stripes and broken rusty yellow spiracular stripes.

This species overwinters as a pupa buried in the soil. Adults emerge in June. Eggs are laid singly on needles and hatch in about 14 days. Larvae are present from June to August, and pupation occurs from late July to August.

Life cycle (East of the Rockies)

Life cycle (East of the Rockies)
Stage/Month J F M A M J J A S O N D

Canadian Forest Service Publications

Green larch looper

Diet and feeding behaviour

  • Phyllophagous : Feeds on the leaves of plants.
    • Free-living defoliator: Feeds on and moves about freely on foliage.
Information on host(s)

Main host(s)

Tamarack, western larch

Secondary host(s)

Balsam fir, black spruce, eastern hemlock, eastern white pine, Engelmann spruce, European larch, jack pine, juniper, lodgepole pine, ponderosa pine, red spruce, Rocky Mountain Douglas-fir, western hemlock, western white pine, white spruce


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