Douglas-fir tussock moth
Last updated on January 29, 2024The 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
Females and eggs
Egg masses
Hatching larvae
Frass
Male moth
Type: defoliator
Targets: Douglas-fir
Life cycle: one year; adulthood from late July to early September
Damage: defoliated trees appear scorched and may die after one or more years of severe defoliation