Douglas-Fir Tussock moth caterpillars, Orgyia pseudotsugata, are major defoliators of spruce, true firs, and of course, Douglas-firs in the western U.S. The young caterpillars feed exclusively on new growth, but mature larvae will feed on older foliage. Large infestations of Douglas-Fir Tussock moths can cause severe damage to trees, or even kill them.
A single generation lives each year, with the larvae hatching in late spring when new growth has developed on the host trees. As the caterpillars mature, they develop their characteristic dark tufts of hair at each end. In mid to late summer, caterpillars pupate; the adults appear from late summer to fall. Females lay eggs in masses of several hundred in fall. The Douglas-Fir Tussock moth overwinters as eggs, entering a state of diapause until spring.