Douglas-fir tussock moth

The Douglas-fir tussock moth is a destructive native defoliator of Douglas-fir. This moth kills trees, and the caterpillars' hairs are a serious human health risk.

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Description

Outbreaks begin as a local infestation then spread into larger areas. Douglas-fir tussock moths occur only in low-elevation stands.

Patterns of defoliation are limited because female moths don't fly and larvae are dispersed by ballooning using silk in wind.

Host tree species

Primarily Douglas-fir, occasionally ponderosa pine and western larch.

Life cycle

The tussock moth has a one-year life cycle. Adults emerge in late July to early September. Males emerge before females and fly in search of flightless females.

Eggs overwinter on the foliage. Larvae hatch in late spring and feed on the current year’s foliage. As the larvae mature, they feed on both old and new foliage. In late July the larvae pupate and emerge two weeks later as adults to disperse.

Damage

Douglas-fir tussock moth outbreaks can cause extensive mortality of interior Douglas-fir. Not only does this insect damage host trees, but the caterpillar's tiny hairs break off and can cause an allergic reaction.

Identification images

 

Close up of tussock moth larvae

 

larvae stretched out to show the bodylarvae from aboveFront close up of a caterpillar

 

yellow frass on a road