Orgyia vetusta

Distinguished from Orgyia antiqua (Vapourer Moth) by geographic range—O. vetusta is western North American while O. antiqua is Palearctic. Distinguished from Orgyia pseudotsugata (Douglas-fir Tussock Moth) by larval coloration: O. pseudotsugata larvae have two prominent dorsal white hair tufts and lack the red lateral dots present in O. vetusta. Adult males of Orgyia species require genitalia examination or geographic context for reliable identification. The wingless female form is diagnostic for the genus Orgyia but not for species-level ID.

Adult males have grayish-brown forewings with darker markings and feathery antennae. Females are wingless, with a robust, grayish body covered in dense hair. Larvae display prominent hair tufts: four cream-colored tussocks on the back, paired red dots on the sides, and a distinctive black head with white markings. The body is covered with long, irritating hairs.

Found in mixed conifer and hardwood forests, particularly those containing oak, Douglas-fir, and other host trees. Occupies elevations from sea level to montane zones. During outbreaks, larvae may defoliate extensive areas of suitable forest.

Pacific States of the United States (Washington, Oregon, California), British Columbia in Canada, and an isolated population in Boise County, Idaho. Ranges eastward to New Mexico.

Adults are active from late spring through summer, with timing varying by latitude and elevation. Larvae feed through summer and early autumn. Pupation occurs in cocoons attached to host trees or debris, with adults emerging the following season.

Larvae feed on foliage of various woody plants including oaks (Quercus spp.), Douglas-fir (Pseudotsuga menziesii), manzanita (Arctostaphylos spp.), and other broadleaf and coniferous trees.

• Quercus - larval food plantoaks
• Pseudotsuga menziesii - larval food plantDouglas-fir
• Arctostaphylos - larval food plantmanzanita

Eggs are laid in a mass on or near the female's cocoon. Larvae hatch and feed gregariously in early instars, becoming solitary later. They develop through five instars, pupating in silken cocoons incorporating body hairs. Adults emerge after overwintering as pupae; females call males with pheromones and lay eggs on their cocoon without dispersing.

Larvae are gregarious in early instars, dispersing as they mature. Females are sedentary, remaining at their cocoon and emitting pheromones to attract flying males. Males are strongly attracted to light. During outbreak years, larvae may descend from trees on silk threads to find new hosts.

Larvae function as herbivores that can substantially reduce leaf area of host trees during outbreaks, potentially affecting forest productivity. The species serves as host for parasitoid wasps including Pimpla sanguinipes (Ichneumonidae), which contributes to population regulation. Larval hairs may irritate vertebrate predators, providing defensive protection.

Periodic outbreaks cause defoliation of forest and shade trees, occasionally reaching levels of economic or aesthetic concern. Larval hairs can cause skin irritation in sensitive individuals. The species is monitored by forestry services as part of integrated pest management programs.

• Orgyia pseudotsugataDouglas-fir Tussock Moth overlaps in range and host use; distinguished by larval pattern (two white dorsal tufts vs. four cream tussocks and red dots in O. vetusta) and preference for fir over oak.
• Orgyia antiquaVapourer Moth is Palearctic in distribution; O. vetusta is strictly Nearctic. Larvae of O. antiqua have different color pattern with yellow and black tussocks.

• tussock moth
• forest pest
• wingless female
• western North America
• defoliator

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