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Powder Post Beetles


Most people in Maine don’t think about the possibility of insects destroying their house; if they do, carpenter ants and termites would be the critters that come to mind. But there is another insect that most people have never heard of that can cause as much damage as either of their more well known cousins- the powderpost beetle.


Powderpost beetles attack slightly damp seasoned hardwood, and are often discovered in stored lumber, rafters, joists, and furniture. They usually enter lumber while it is being stored and cured at the lumberyard, then later emerge from the finished product (possibly house structural lumber). When they exit, they leave tiny holes (1/32” to 1/16” in diameter). These holes aren’t very damaging, the problem is that if the conditions remain optimal, the beetles can re-infest the wood year after year laying their eggs in the lumber and repeating the cycle. Over time the wood becomes completely riddled with tunnels and galleries packed with powdered wood called frass. The length of the life cycle of powderpost beetles can range from 3 months to 5 years, influenced by the wood’s nutritive content and by environmental conditions.


If the conditions are right, multiple generations of beetles can re-infest one piece of lumber for decades, while the neighboring boards are left unscathed. This was the case on a recent inspection of a dirt floored crawlspace. One section of the house’s rim joist looked to be in good condition but was hollow when gently tapped on. On further inspection tiny holes could be seen. The outermost layer of wood was paper thin and broke when gently prodded. Once the skin of the wood broke, a large pile of frass spilled out, essentially the entire interior of the board had been turned into powder. The other lumber in the area looked to be intact. Due to the damage, the joist had to be replaced. Once the infest lumber containing the beetles and their larvae are removed, no further action is needed. However in a crawlspace it is difficult to see the tiny holes making it difficult to be sure there was no further infestation. Therefore chemical treatment is generally required to ensure there are no other infested boards. Reducing the moisture content is the best prevention; in this case installing a vapor barrier on the floor of the crawlspace would be helpful. So once again our advice is to keep wood dry!


If you have wood in any damp areas, periodically check it for active infestation: tiny holes with frass beneath, progressing to weakened wood with powder filled tunnels and galleries. Consult a professional for structural repair and pest removal.



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