What’s that sound inside your tree? It might be wood borers at work

golden buprestid (Buprestis aurulenta)
Cool paint job! Although similar in appearance to destructive emerald ash borer, this native Washington metallic wood borer species — golden buprestid (Buprestis aurulenta) — rarely kills healthy trees. Photo: Melissa Fischer/DNR.

I hear bugs chewing the wood inside my trees!

Washington DNR stewardship foresters say that forestland owners sometimes call and say they can hear bark beetles feeding in their trees. Although bark beetles may be present in those trees what these landowners are likely hearing is wood borer activity. Wood borers tend to be much larger than bark beetles and, therefore, are more likely to be heard chewing away inside trees.

While bark beetles feed solely on a tree’s phloem, wood borers feed on sapwood and heartwood as well as phloem. Native wood borers attack stressed, dying, or dead trees; there are very few native species that actually kill trees.

Wood borers are attracted to volatile gases released by dead or dying trees and lay their eggs under the bark of these trees. Once the larvae hatch, they begin feeding on the inner bark and then tunnel into the wood. The larvae are white, legless grubs and can be quite large. They are valued as a food source by woodpeckers (they make great fishing bait too!) and woodpecker activity is often seen on trees that contain wood borers. The tunnels produced by larval feeding activity have a random pattern and increase in size as the larvae grow.

Frass (beetle poop) is likely to be present within the tunnels. Unlike bark beetle frass, which is fine and reddish in coloration, wood borer frass tends to look more like shredded wheat and is white in color.  When wood borers develop into adults, they emerge from trees and leave exit holes that are typically quite a bit larger than those left by bark beetles.

Wood borers play an important ecological role by introducing wood decaying organisms into dead and dying trees which, in turn, helps to speed nutrient cycling. Typically, no management is necessary for native wood borers in a forested setting. Wood borers can damage lumber, but damage is unlikely to occur if the wood has been treated.

Types of wood borers

There are three common wood borer families; Cerambycidae, Buprestidae, and Siricidae. Click here to see descriptions and slightly creepy close-up photos of these little guys in the latest issue of Forest Stewardship Notes, a free, quarterly e-newsletter published quarterly by DNR and the Washington State University Forestry Extension program.

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