When pin-sized holes and “sawdust” are discovered on hardwood floors, the culprit is usually a powderpost beetle. There are two types of powderpost beetles, lyctids and anobiids, that could infest the floor but lyctids are the usual culprit. Only an expert can tell the difference.
When powderpost beetles show up in hardwood flooring, the question is often, “who is responsible? Were the beetles in the wood when the floor was installed by the contractor, or did they infest after installation?” It’s important to know which type of powderpost beetle you are dealing with to come up with the answer.
If it’s lyctid powderpost beetles, the answer is usually “yes, the beetles were probably already in the wood.” Lyctid beetles infest seasoned hardwood, usually during the time that it is drying or is stored. The longer wood is stored, the higher the risk of infestation. If it is instead anobiid powderpost beetles, then the answer may be “no, the beetles could have infested after the floor was installed.” You’ll see why below.
If the floor was infested after installation, the beetles had to come from infested wood below the floor since powderpost beetles never lay their eggs on sealed wood, meaning wood that has been varnished, polished, waxed, painted, or sealed with polyurethane. Virtually every newly installed hardwood floor will be sealed in some manner.
If the floor is infested by lyctid powderpost beetles, it’s unlikely (although not impossible) that the larvae would bore into the floor from an infestation below since plywood subflooring and floor joists are almost always made from softwoods and lyctid powderpost beetles infest only hardwoods. But anobiid powderpost beetles can infest both softwoods and hardwoods so they could enter the bottom side of a hardwood floor from floor joists below. You see why you need to know what type of beetle you’re dealing with before you can lay blame on the floor installer.
Fortunately, in most cases the infestation is limited to one or, at most, a few floorboards that will have to be replaced. An expert should check the subflooring beneath to see if there is any evidence of infestation there as well. “Will emerging beetles reinfest the flooring or other wood objects in the home?” Powderpost beetles can reinfest the same wood they came out of or other wood if conditions (mainly moisture) allow. In most cases, however, other wooden items in a home will be too dry or will be painted or sealed, and the infestation will die out.