Bark Beetles in Trees and Firewood

Description of bark beetles

Bark beetles feed and develops within the cambium layer just under the bark of trees.  They are widespread, common and frequently abundant.  Bark beetles are found in trees that are under stress or are in the process of dying.  They are also common in firewood cut from recently-dead or cut trees.  There are hundreds of species of bark beetles.  Most are host plant specific and will attack only one species of group of related trees. 

Bark beetle emergence holes.  Photo by DR Lewis.
Bark beetle emergence holes.  Photo by DR Lewis.

Life cycle of Bark beetles

Bark beetles are small (1/16 to 1/8-inch in length) cylindrical, brown to black beetles.  Adults typically appear in the spring and females deposit eggs in galleries just under the bark.  The eggs hatch into small white legless larvae with brown heads. The larvae tunnel under the bark as they eat and grow, producing winding tunnels between the bark and the sapwood of the tree.  New adults emerge through small round exit holes in the bark.  There may be 2 or 3 generations of beetles produced each season and dying trees, logs or firewood may contain hundreds of individuals.

Damage caused by bark beetles

Bark beetle attack of trees, logs or firewood is recognized by powdery, sawdust-like frass created as the beetles chew and tunnel under the bark.  Small, buckshot-sized emergence holes indicate past bark beetle activity as most of the holes are made when the beetles emerge from infested wood.  Small winding tunnels or galleries (less than one-eighth inch wide) under the loose bark show where bark beetles were feeding.

Bark beetles are usually a secondary problem in the landscape.  Most bark beetle species attack trees that are severely stressed or dying.  They do not cause trees to decline or die but rather are taking advantage of a tree weakened by previous events or circumstance (even though the tree may not outwardly appear compromised).  Newly transplanted trees are particularly susceptible to attack.  Healthy, well-established trees are rarely successfully attacked by bark beetles.

Management of bark beetles 

Bark beetle galleries.  Photo by Pennsylvania Department of Conservation and Natural Resources via
Bark beetle galleries.  Photo by Pennsylvania Department of Conservation and Natural Resources via

Control of bark beetles is usually not practical after they are established inside a tree (as evidenced by numerous emergence holes or loose bark).  Prune and discarded bark beetle-infested limbs and trees.  Prevent bark beetle problems by promoting tree vigor through proper site selection, planting, mulching, watering, pruning, and avoidance of injury.  Insecticide sprays are not effective when applied to trees that are already heavily infested. 

Bark beetles attack green logs and firewood for one or two seasons following cutting but do not attack cured wood or lumber.  Bark beetles that emerge inside the house can be annoying and a source of anxiety.  However, they are never a threat to people, furniture or the house structure.  Spraying infested firewood is of no practical benefit and is not advised.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.  


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 12, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.