Skip to content

What's bugging Alaska's forests? Spruce beetle facts and figures

  • Spruce beetles are only ¼ inch long.
  • Spruce beetles infest Sitka, white and Lutz spruce (white/Sitka hybrid) most often, and attack black spruce only rarely.
  • Beetles live in the thin, phloem (growing) layer between the bark and the wood. Therefore the wood remains undamaged by the beetles and useable for construction for some time.
  • One female beetle may lay from 10 to 150 eggs in "galleries" constructed beneath the bark in the phloem tissue.
  • A large, downed spruce tree may contain more than 100 beetles per square foot of bark.
  • Beetles emerge from infested tree and fly to new host trees from mid-May until mid-July (when temperatures are above 60° F).
  • Spruce Beetles feed and breed on wind-thrown, fallen or injured trees wherever there are spruce forests. When conditions are right, beetle populations may outgrow the supply of down trees and move into nearby living trees, especially mature spruce stands.
  • Recent annual statewide aerial surveys have indicated that the ongoing spruce beetle outbreak in Southcentral Alaska has impacted more than 900,000 cumulative acres from 2016-2018. Statewide, nearly 600,000 acres of ongoing spruce beetle activity was mapped in 2018.
  • Human activities such as fire suppression and improper disposal of slash enhance conditions for beetle outbreaks; as do natural occurrences such as wind-thrown, fire-scorched or flood-damaged trees.
  • Fast growing, healthy trees are more resistant to beetle attacks than slow growing unhealthy trees.
  • Beetles can emerge from infested firewood and attack living trees.
  • Beetles produce chemicals called pheromones to communicate with other beetles – for mating, to locate susceptible host trees and to repel other spruce beetles. Spruce trees also produce chemicals that affect beetle behavior. These chemicals show potential for modifying beetle behavior and reducing the severity, or even preventing, damaging infestations.
  • Some EPA-approved insecticides have provided 100 percent protection from beetle attacks for at least two years, based on research results.
  • More detailed information about the spruce beetle can be obtained from a forest pest leaflet published by the USFS in response to the 1990s epidemic: spruce beetle FIDL #127

Spruce Beetles in Firewood

Spruce beetles attack and breed only in spruce. Birch, hemlock, aspen, cottonwood and other trees are not at risk. Spruce beetles spend most of their life in the phloem tissue between the bark and the wood of a host tree. Adult beetles emerge in the spring and bore through the bark of a new host tree. Female beetles excavate galleries in which to lay eggs. The newly hatched larvae create feeding tunnels at right angles to the larger egg galleries, where they complete their one or two year life cycle.

If numerous beetles attack the tree, the resulting brood can girdle and kill the tree. Spruce beetles prefer to attack recently windthrown trees, but they also attack and kill standing trees that are weakened or diseased. Slow growing and less vigorous trees are also attacked when conditions favor beetle dispersal.

Trees killed by spruce beetles are often used as firewood. During the first winter after infestation both larvae and adult beetles may be present under the bark. Adult beetles may also be under the bark around the base of the tree through the second winter, and may emerge the following spring. Two years after the attack, beetles have left the tree. A two-year life cycle is most common in South-central Alaska.

Adult beetles over-wintering under the bark of firewood emerge when warmer weather arrives and seek out new host material, often a valuable landscape tree near the woodpile. By examining spruce logs to be used for firewood, and following suggestions below, you may avoid spruce beetle infestations in your live standing trees.

Condition of spruce firewood and ways to reduce beetle populations:

Fresh log with green needles when cut; bark peels away from wood smoothly; wood not split.

  • Store only enough firewood for a single winter’s use.
  • Split into stove-size pieces to dry out; stack loosely or separate to allow maximum air circulation.
  • Dry wood discourages new spruce beetle attacks.
  • De-bark log to eliminate potential beetle habitat.

Fresh log with green needles when cut; visible beetle attacks on bark surface (reddish-brown boring dust and pitch globules); bark may peel smoothly; wood not split.

  • Store only enough firewood for a single winter’s use.
  • Split into stove-size pieces to dry out; stack loosely or separate to allow maximum air circulation.
  • This will dry out the larvae and their food source.
  • De-bark log to eliminate larvae and habitat.

Dry log; rust colored or no needles present on tree when cut; some evidence of old beetle attacks or woodpecker activity; bark may adhere tightly or pull off in pieces.

  • Split and use prior to next spring to kill adult beetles that will emerge at that time.
  • Fire-scorch the outer portion of the bark, killing beetles beneath, but keep the bulk of the wood
  • intact (messy, but intact) for future use.
  • Consider preventive measures on surrounding live spruce trees.

Dry, old log or split wood; barks pulls off loosely

  • Spruce beetles will not attack well-seasoned wood and are normally gone from trees that have been dead for more than one year ( though beetles and other insects may enter the wood). Old wood, free of spruce beetles, is not a potential spruce beetle infestation source.

For more information:

Alaska Division of Forestry Forest Health Program
(907) 269-8460