Pest profile

Douglas-fir Tussock Moth

Orgyia pseudotsugata · Lepidoptera: Erebidae[2]

Douglas-fir tussock moth caterpillars chew the needles of spruces, Douglas-fir and true firs; in Colorado Front Range towns, blue spruce suffers most.[1]

Douglas-fir tussock moth caterpillar with long black tufts at the head and rear and orange-brown hair patches, on wood
Douglas-fir tussock moth caterpillar with long black tufts at the head and rear and orange-brown hair patches, on wood. (c) CK2AZ, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Mature caterpillars are 1.2 to 1.4 inches, gray to brown with a shiny black head, two long black tufts pointing forward and one backward.[1]
  • They carry dense light brown hair patches with red spots and an orange stripe along each side.[1]
  • Females are wingless and lay egg masses covered with gray hairs on their cocoons; males have rusty forewings.[1]

Where it lives

CSU Extension covers outbreaks in Colorado landscapes, often near forests, where windblown young caterpillars start infestations.[1]

US map: public records from 11 states since 1990 (GBIF).

Biology and life cycle

Eggs overwinter and hatch around bud break, often in late May; tiny caterpillars balloon on the wind to new trees.[1]

Larvae are full grown by mid-July or August, pupate nearby, and moths emerge late July to mid-August; one generation a year.[1]

Damage and signs

  • Feeding starts at the top of the tree on new growth; tops can die after a single season of severe defoliation.[1]

Health risk

The caterpillars' hairs can irritate skin and cause a painful rash, though reactions vary widely between people.[1]

Control

Prevention

Survey host trees for egg masses in winter or early spring; few egg masses mean little risk next year.[1]

Biological control

Parasitoids, predators and especially a virus that causes wilt disease usually end outbreaks within a season or two.[1]

Pesticides

If needed, spray the treetop new growth soon after egg hatch, when young larvae are easiest to kill.[1]

Common questions

Can I touch tussock moth caterpillars?
Avoid it; their hairs can cause a painful rash in some people.[1]
What are the caterpillars hanging limp from my spruce?
They're likely 'hangers' killed by a virus that often ends tussock moth outbreaks.[1]

Sources

  1. Colorado State University Extension, “Douglas-fir Tussock Moths (Fact Sheet 5.542).” extension.colostate.edu/resource/douglas-fir-tussock-moths/ (accessed 2026-10-06)
  2. iNaturalist, “Orgyia pseudotsugata taxon page (order and family).” www.inaturalist.org/taxa/48907 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.