The Douglas-Fir Moth

Douglas-Fir Tussock Moth Caterpillars

• Immature Douglas-fir tussock moth caterpillars are black and adorned with long hairs on their body that take on different, bright colors as the caterpillar grows larger. When mature, the caterpillar becomes gray or brown with a black head and a length just under 1 1/2 inches. Two distinct tufts of black hair jut forward from both the head and rear, while red spots and an orange stripe adorn each side of the insect's body.

Lifecycle

• The eggs of the moth spend the winter attached to cocoons hidden within the tree and hatch in late spring. The young caterpillars move upward into the fir tree, with some blown by the wind to adjacent trees. They feed on new foliage that wilts and turns brown, then move on to older needles. Especially when disturbed, the Douglas-fir tussock moth caterpillar enjoys the ability to move from branch to branch via silken strands it produces.

Adult Moth

• Reaching maturity in late summer, the caterpillar spins a brown cocoon and pupates into an adult moth. The Douglas-fir tussock moth (Orgyia pseudotsugata) is a brown-charcoal moth with a wingspan of a little over 1 inch. The eggs it lays -- as many as 300 -- are gray and mixed into a gelatinous secretion and a mass of hairs from the body of the female. Unable to fly, the wingless female deposits the eggs on the top of the cocoon that once housed her.

Management

• Producing one generation annually, an infestation of this moth weakens the Douglas-fir and encourages attack from bark beetles and the Douglas-fir beetle. Chemical sprays are effective in reducing the population of moths, but do not prevent reoccurrence. Pesticides should be applied after the larvae have hatched and begun to feed. Birds, ants and spiders are natural predators. Gardeners wishing to remove the caterpillar by hand should employ caution, as the long hairs of the caterpillar cause irritation and a rash on the skin of humans.