Powder-post beetles damage wood by tunneling and by cutting surface holes.
Tunneling is done by the larvae of all kinds of powder-post beetles, and by adult bostrichids and cossonid weevils. The larvae of anobiid beetles leave elongate pellets of excreted wood in their tunnels. Other larvae leave powderlike borings. Severely damaged wood becomes a crumbly mass of pellets or of borings, and sometimes has a honeycombed appearance.
Since the insects do most of their tunneling in sapwood, structural damage is rare in large timbers.
Surface holes mar the appearance of wood. Those most commonly seen are made by adult beetles when they emerge from the wood. Those made by many of the smaller beetles are about ⅛ inch in diameter. They give wood the appearance of having been hit by buckshot, and are called shotholes. Larger beetles make holes ¼ to ⅜ inch in diameter.
Emergence holes made by the old house borer are oval. The lengthwise measurement is about ¼ inch.
The larvae of some species, including the lyctus beetles, make holes to the surface of the wood and expel borings through them. The larvae of the old house borer seldom pierce the surface; they pack their borings behind them.
DETECTION
Aside from observing tunneled wood, there are several ways of detecting powder-post beetle damage.
You may see surface holes, or borings that have been ejected from them. The borings may be in piles near the holes or, where timbers overhead are attacked, they may be on the floor below.
You may see adult beetles crawling on the wood.