By Chris Williams on April 5, 2017.

I am in the process of finishing off a room in our basement and found lots of tiny and perfectly round holes in a wooden joist. In one corner I could see little piles of powdery sawdust but I didn’t find any termites or anything else. Do you know what caused this? T. R., Pinardville, NH

From your description of the holes and frass (the powdery sawdust), I’m pretty sure that the culprits were powderpost beetles. Because of the location of the damage and the type of wood, I’m guessing that you are dealing with one of the anobiid powderpost beetle species. This beetle is common in the eastern U.S. and is probably the most destructive of the bunch since it tends to attack softwoods in joists and studs.

Depending on the anobiid species, they can attack either softwoods or hardwoods, and structural timbers or manufactured wood products. In some cases, they may cause structural damage when they infest joists and other structural members. Most species attack wood that is older than 10 years. Because anobiids have a high moisture requirement, they are more of a problem in wood in constantly damp areas such as crawlspaces or basements.


The female beetle lays eggs on the surface of desirable wood and the hatching larvae bore inside and begin feeding. If you break open a piece of beetle-infested wood, you will find tunnels or galleries made by the feeding larvae (and maybe the larvae themselves). They pack their frass (digested wood) into the tunnel behind them as they move along. When fully-developed, the larvae pupate inside the tunnels and the resulting adult beetle emerges from the wood though a round exit hole that is about 1/10-inch across, pushing powdery frass out as it does so.

In most structures, the larvae inside the wood are relatively inactive during the winter months and resume feeding in early spring. If the infestation is still active, within the next couple of months (late spring to early summer), you should begin seeing new exit holes in the wood with light-colored frass beneath. You may never see the adult beetles that emerge from the holes. They are active only at night; some are attracted to lights. They’re tiny (you can tell that by the size of the holes), only about 1/32 to 3/8-inch long, reddish-brown to dark brown.


Since anobiid powderpost beetles can re-infest wood if conditions are right, you can’t assume that once the adult beetles emerge the infestation is over. I don’t think you ought to wait around to see if new holes appear, however, especially if you are in the process of renovating the area.


Call Colonial Pest first for a thorough inspection by one of our trained professionals. In the meantime, take a photo of the existing holes or circle them so any new holes will be apparent. The results of our inspection will confirm the pest, verify if the infestation is active,  and determine the type of control method that would be best. Controls can range from simple replacement of infested wood, to treatment of the wood with a borate product that penetrates and kills the larvae inside.


For more on powderpost beetles, see “Shot Holes” in Wood.

Photo Credit : By No machine-readable author provided. KaiMartin assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, Link



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