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Western oak looper

Western oak looper -
  • Latin name: Lambdina fiscellaria somniaria (Hulst)
  • French name: Arpenteuse occidentale du chêne
  • Order: Lepidoptera
  • Family: Geometridae


British Columbia

This species is distributed throughout the range of Garry oak in south coastal British Columbia; it also occurs south to Oregon.


Leaf, Needle

Damage, symptoms and biology

The western oak looper periodically causes localized severe defoliation of Garry oak as well as Douglas-fir occurring in or adjacent to infested oak stands. Garry oak tolerates repeated defoliation reasonably well whereas Douglas-fir often is seriously weakened and may subsequently be attacked and killed by Douglas-fir beetle. Outbreaks were recorded in the Christmas Hill area of Victoria from 1946-1948 and again from 1958-1962; a recurring outbreak continued on Mount Maxwell, Salt Spring Island from 1978-2002.

Mature larva up to 30 mm long. Head, brown with eight prominent black spots. Body, light to dark grey, complex pattern of alternating grey to cream-coloured longitudinal lines; four prominent dark spots on the dorsum of each abdominal segment.

This species overwinters as eggs laid on moss, lichens or bark. Eggs hatch from late May to early June. The young larvae initially feed on the new foliage; as the larvae mature they feed on foliage of all ages. The larvae are wasteful feeders and leave behind partially consumed needles or skeletonized oak leaves. Larvae are present from June to early September. Pupation occurs on foliage, tree trunks or in the duff from late July to early September. After a 10- to 14 day pupation, adults emerge and are in flight from September to October.

Canadian Forest Service Publications

Western oak 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)

The principal coniferous host of western oak looper is Douglas-fir; it is otherwise restricted to Garry oak.

Main host(s)

Garry oak, Rocky Mountain Douglas-fir


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