Silver fir beetle and fir root bark beetle

How to identify it

• Both are stout, oval beetles covered in brown and gray scales that give a patchy appearance; rub the scales off and the body is minutely roughened, shinier and dark reddish-brown to black. The thorax is distinctly narrower than the wing covers, which have shallow irregular punctures, narrow lengthwise lines and are strongly rounded at the base.^[1]
• Size separates them. The fir root bark beetle averages 4.0 to 6.5 mm long (0.16 to 0.26 inch); the silver fir beetle is about 2.4 to 3.9 mm (0.09 to 0.15 inch).^[1]
• Entrance holes sit in bark crevices and under bark scales, moss or lichen and are easy to miss. Fresh attacks leave small amounts of reddish boring dust, and heavy attacks ring the base of the tree with dust that is visible from 10 or 15 feet away until the first rain washes it off.^[1]
• Under the bark the egg gallery cuts across the grain, 1 to 7 inches long and averaging 2.6 inches, with larval mines running perpendicular to it along the grain. The Idaho guide gives the fir root bark beetle's galleries as irregularly transverse, 2 to 18 cm long, from the trunk base to about 5 m up.^[1][2]

Look-alikes

Where it lives

The silver fir beetle is confirmed from British Columbia, Alaska, Washington, Oregon, Idaho and California, from the southern Alaskan peninsula near Sitka and western British Columbia south to the Santa Cruz Mountains of central California and east to the Cascades. The fir root bark beetle is confirmed from the same states plus Montana, from near Juneau south to the Giant Forest in Sequoia National Park and east to the western edge of Montana. In Idaho the fir root bark beetle is recorded from Clearwater, Kootenai, Latah and Valley counties and the silver fir beetle from Clearwater and Idaho counties.^[1][2]

US map: public records from 2 states since 1990 (GBIF). View the map

Biology and life cycle

In northwestern Washington both beetles take about 24 months to complete a generation; at warmer, lower-elevation sites they may reach adulthood within a year.^[1]

There are two kinds of attack. New adults emerge between August and early September and make feeding attacks, boring into the living phloem without building galleries or laying eggs; from late September to the end of October they concentrate at the bases of host trees and hibernate there. In late May to early June the overwintered beetles emerge and make brood attacks, constructing galleries and laying eggs in niches along them, and in late July or early August some re-emerge to build more galleries and lay a second batch. From the outside the two attack types look identical, and only removing a patch of bark shows whether galleries are present.^[1]

Larvae hatch in 10 to 14 days and mine away from the parent gallery, at first in parallel and then wandering as they grow and crowd each other. The larval stage lasts 12 to 14 months depending on when the eggs were laid, and development stops in cold weather, so larvae and an overlapping generation of adults both overwinter. The following July mature larvae build pupal cells in the inner bark, and the adults emerge two to three weeks later.^[1][2]

The Idaho guide adds that adult progeny emerging in August excavate short hibernation tunnels, 6 to 15 mm long, in the bark rather than the cambium, and that several adults may enter one tunnel and make separate niches in it.^[2]

A brown-staining fungus, Ophiostoma subannulatum, is often associated with both beetles and is believed to help kill the tree. Feeding scars on living trees can also open the way for root-rot fungi: Armillaria ostoyae was present to some degree at the base of every beetle-killed silver fir in a 1954 study in Skagit County, Washington.^[1]

Damage and signs

• Infested trees fade yellow, then bright red-orange, then dull red-brown, and the dead needles hang on for up to two years; in unseasonably warm weather the needles may die and fall without the colour change. Yellow and bright red-orange crowns mean a freshly killed tree that often still holds larvae.^[1]
• Killing a mature tree usually takes more than a year. A tree may be top-killed one year and lose more sections later, and strip or patch-killing is common, so it is not girdled in one season; some strip attacks heal over and leave scars, but repeated attacks over several years generally finish the tree.^[1]
• Pacific silver fir is the usual host and the only one with serious epidemics, though both beetles are recorded from grand, white, California red, subalpine and noble fir, Douglas-fir and western hemlock. Pole and sapling-size trees in dense stands and suppressed understory trees are the most susceptible. Outbreaks are rare: one from 1947 to 1955, worst in Oregon and Washington, killed more than 528 million board feet of Pacific silver fir on over a million acres, and a 1994 to 1997 outbreak near Vancouver killed a few hundred silver firs after a blowdown.^[1]

Health risk

Forest insects with no reported effect on people; the leaflet describes damage to true firs only.^[1]

Control

Prevention

Young, vigorous trees appear resistant, so forest practices that keep tree vigour up are what reduce impact. The big 1947 to 1955 outbreak was associated with drought, with above-normal temperatures and below-normal precipitation through the 1940s and early 1950s and hot dry summers starting it, and the beetles have also been linked to tree-killing where sawflies defoliated stands or balsam woolly adelgid damaged trees.^[1]

Sanitation

Remove windthrown trees where that is feasible, since downed and injured fir is the material these beetles build up in. A coastal Oregon study found silver fir beetles also attack fresh western hemlock logging slash in recently thinned areas.^[1]

When to call a professional

Private landowners wanting help with a fir mortality problem can contact county extension agents or their state forestry or agriculture department; federal land managers go to Forest Health Protection.^[1]

Related profiles

• Fir engraver
• Western balsam bark beetle
• Douglas-fir Beetle
• Spruce Beetle

Common questions

How do I tell the two apart?

By size and by where on the tree they are. The fir root bark beetle is the larger (4.0 to 6.5 mm) and attacks from a few inches below ground up to about 15 feet on the trunk; the silver fir beetle is smaller (2.4 to 3.9 mm) and works the upper bole and branches, down to limbs an inch thick.^[1]

The bark has boring dust but I can't find galleries. What is going on?

You may be looking at a feeding attack. New adults bore into the phloem in late summer and fall without making galleries or laying eggs; brood attacks the following spring look the same from outside, and only bark removal distinguishes them.^[1]

Will these beetles kill a healthy fir?

Young, vigorous trees appear resistant. These beetles usually take windthrown, felled, injured, suppressed or already weakened trees, and even then killing a mature tree typically takes more than a year of repeated attacks.^[1]

Sources

1. USDA Forest Service, Pacific Northwest Region, Forest Health Protection, “Forest Insect & Disease Leaflet 60: Silver Fir Beetle & Fir Root Bark Beetle (Carlson and Ragenovich, revised April 2012).” www.fs.usda.gov/foresthealth/docs/fidls/FIDL-60-FirBeetles.pdf (accessed 2026-11-10)
2. University of Idaho, Idaho Forest, Wildlife and Range Experiment Station, “Furniss and Johnson. Field Guide to the Bark Beetles of Idaho and Adjacent Regions, Station Bulletin 74 (2002).” objects.lib.uidaho.edu/fwres/fwres201.pdf (accessed 2026-11-10)
3. iNaturalist, “Pseudohylesinus sericeus taxon page (order and family).” www.inaturalist.org/taxa/456048 (accessed 2026-11-10)