The new-growth needles of a Douglas fir are shown eaten away, and a few withered, rust-colored needles are bound by the budworm's white web.

Budworm biography

Originally published September 23, 2001

The western spruce budworm is native to the western United States, but recent outbreaks have grown more severe and persistent due to the changed nature of western forests.

- Scientific name: Choristoneura occidentalis Freeman

- Claim to fame: The most widely distributed and destructive defoliator of coniferous forests in western North America.

- Where they live: Washington, Oregon, Idaho, Montana, Wyoming, Colorado, New Mexico, Arizona, Utah and British Columbia. Washington and Oregon have experienced severe outbreaks in the past 20 years.

- Appearance: Adult moths are about half an inch long and have a wingspan of about an inch, with gray- or orange-brown forewings. Larvae, or caterpillars, start as yellow-green with brown heads; they develop orange or light-brown bodies with black heads; in their final stage they have reddish-brown heads and olive bodies with small white spots.

- Life cycle: 12 months

- Females lay eggs in August, which hatch in about 10 days.

- Larvae spin silken hibernation tents for the winter.

- Caterpillars emerge in early May to late June and feed on new growth.

- Around early July, they pupate and emerge as moths in late July or early August.

- Target trees: Douglas fir, grand fir, white fir, blue spruce, white spruce, western larch and others.

- On the Web: www.fs.fed.us/r6/nr/fid

The Olympian Copyright 2001

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