Spruce beetles spend most of their lives under the bark of trees. As such, we rarely see the insects before we see their damage. Knowing how to identify spruce beetle damage to trees is an important first step. The video below shows the signs and symptoms of spruce beetle damage in trees.
If you can’t watch the video right now, the information below can help get you started with identification, too.
The most noticeable symptom of a spruce beetle infestation is the change in needle color of impacted spruce. Following a successful spruce beetle attack, needles will change from healthy green, to faded yellow, and finally to red before the needles eventually drop. This process occurs at varying rates and may take over a year to occur.
Boring dust is a brown sawdust like material that collects at the base of a tree and in bark crevices. It is pushed out of beetle entrance holes as adults excavate and clear their galleries (tunnels) beneath the bark. Other species of insects produce boring dust (e.g. engraver beetles), so further investigation is needed to determine if this is spruce beetle.
Pitch tubes are often found at the site of a beetle attack. Pitch tubes appear as reddish globules on the bark’s surface and are the tree’s attempt to push out invaders. Stressed trees may not be able to produce enough resin, so pitch tubes may be small or absent. The success or failure of this defense can be assessed by examining pitch tubes closely. Large amounts of boring dust in the pitch and an unobstructed entrance hole may indicate beetle success.
Woodpeckers are attracted to the beetle attacked trees and will peck and scrape at the bark to find the beetles beneath it. Woodpeckers remove bark and leave behind flakes of wood at the tree’s base. This may be most noticeable in the winter when the bark accumulates on top of the snow. Additionally, bark beetle predators, most notably checkered beetles, may be seen scurrying along the outer bark of infested trees in search of prey.
Loose bark on a dead tree
After beetle attacks, the trees will dry out and the bark will become loose and fall off.