Orgyia pseudotsugata

Males distinguished by grayish-brown mottled coloration, feathery antennae, and wingspread of 25-34 mm. Flightless females with rudimentary wings are unique among local moth fauna. Caterpillars unmistakable due to combination of red spots, white spines, red-tipped white tussocks, and long black hair tufts at both ends. Similar to Orgyia vetusta (western tussock moth) but associated with different host preferences and geographic range.

Adult males are grayish-brown moths with mottled light and dark markings, wingspread 25-34 mm, with brown hindwings visible when spread. Antennae are plumose (feathery). Northern populations are darker; southern populations lighter. Females are flightless with only rudimentary wings. Caterpillars are 20-26 mm, colorful with red spots, white spines, conspicuous red-tipped white tufts (tussocks), and dense bunches of long black hairs projecting forward and backward.

Coniferous forests of western North America, particularly stands of Douglas-fir, true fir, and spruce. Outbreaks occur across a broad elevational range wherever host trees are abundant.

Western North America: British Columbia, Idaho, Washington, Oregon, Nevada, California, Arizona, New Mexico, Colorado, western Montana. Three subspecies recognized with somewhat different ranges: O. p. pseudotsugata (British Columbia to Idaho, western Montana, eastern Washington, Oregon, Colorado, Nevada, California), O. p. morosa (British Columbia to California), and O. p. benigna (Arizona).

Eggs hatch in spring (May-June). Caterpillars feed through summer. Pupation occurs in July-August within silken cocoons. Adults emerge July/August to November. Females remain near cocoons; males fly to locate mates.

Larvae feed on needles of Pseudotsuga and Abies species, especially Douglas-fir (Pseudotsuga menziesii), grand fir (Abies grandis), and white fir (Abies concolor). Also feeds on true fir and spruce species. Young larvae initially feed on new foliage (current season's growth), later consuming both new and old needles.

• Pseudotsuga menziesii - primary hostDouglas-fir, namesake host
• Abies grandis - primary hostgrand fir
• Abies concolor - primary hostwhite fir
• Picea - secondary hostspruce species

Eggs are spherical, white, laid in protective masses and overwinter. Larvae hatch May-June and progress through instars feeding on conifer needles. Caterpillars produce long silky threads enabling wind-assisted dispersal between branches. Pupation occurs July-August in loose silken webbing forming a cocoon. Adults emerge late summer through November. Flightless females remain at emergence site, emitting pheromones to attract flying males. Because females are sedentary, outbreaks always form in place rather than spreading through female dispersal.

Caterpillars are the primary dispersal stage, using silk threads to drop from branches and catch wind currents. During outbreaks, extensive webbing is produced. Adults are nocturnal; males fly to locate sedentary females. Females do not disperse, remaining at their cocoon site for mating and oviposition.

Periodic outbreaks cause extensive defoliation of conifer forests, temporarily altering forest structure and nutrient cycling. Outbreak collapse may be mediated by natural enemies including viral pathogens and parasitoid wasps. Serves as host for parasitoid wasps including Pimpla sanguinipes (Coccygomimus sanguinipes). Defoliation events create pulses of dead needle litter and alter understory light conditions.

Major forest pest in western North America; outbreaks cause timber loss, tree mortality, and increased fire risk. Management includes pheromone trap monitoring for early detection, silvicultural techniques, and aerial application of carbaryl. Outbreaks typically subside naturally after 1-4 years. Economic impacts on forestry industry and forest ecosystem services.

• Orgyia vetustaWestern tussock moth; similar caterpillar appearance with tussocks and hair tufts, but different geographic distribution and host associations
• Orgyia antiquaVapourer moth; related tussock moth with flightless female, but Palearctic distribution and different color pattern
• Lymantria disparGypsy moth; also causes cyclical outbreaks and defoliation, but males and females both winged (though females weak fliers), and different caterpillar appearance

• forest pest
• cyclical outbreak
• sexual dimorphism
• conifer specialist
• western North America
• tussock moth
• flightless female

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Bug Eric: National Moth Week Recap, 2015
• Bug Eric: Wasp Wednesday: Pimpla sanguinipes
• Plant hunting in South Essex - Buglife Blog - Buglife