Beetles That Infest Hardwood Floors

How does wood flooring get infested?

There are a number of insects that use dead trees, or cut lumber, on which to lay eggs and develop their young. Insect larvae feed on starch reserves in the wood that were formed when the tree was alive. Most of these insects, however, cannot infest live trees because of the tree's natural defenses.

Powderpost beetles lay their eggs on the bare wood surfaces. Tiny beetle larvae bore in through small surface cracks and larvae develop by consuming starch stored in wood cells. Extensive internal damage can be done by the boring larvae. Larvae take months or years to complete development and adult beetles emerge through circular emergence holes (right) on the wood surface.

Wood may be infested even after it has been kiln-dried and milled into lumber. Infestation occurs when dried wood is improperly stored near an active infestation (see below). This is counter to what some flooring manufacturers claim. Kiln-drying alone does not confer protection against infestation but it does eliminate any larvae that were present at the time the wood entered the dryer.

Is the beetle infestation active?

This is one of the first questions usually asked. Since emergence holes are permanent it is impossible to know for certain if the infestation is active because you find holes in the floor. The best indication of an active infestation is the presence of fine, powdery boring dust associated with emergence holes. Another good indicator is the condition of the emergence holes themselves.

Use your hand lens to look carefully at the emergence holes under a good light. If the walls of the hole are covered with finish (below right) you can conclude that the holes were made before the finish was applied and may indicate a old, inactive infestation. On the other hand, if the walls appear fresh you might conclude that beetles emerged recently indicating an active infestation.

Elongated emergence holes (right) also indicate that the holes were made before the wood was cut into flooring. Emergence holes are normally round. Elongated holes occur when a round tube is cut at an angle to the original surface.

Another way to distinguish active from inactive infestations is to mark all existing holes with a grease pencil so that new ones can be spotted. You probably won't find beetles flying around the room.

How to stop wood destroying insects (pre-installation)

There are two manufacturers that supply products to protect new floors from wood destroying insects and fungi. These products are based on insecticidal borates. Bora Care (Nisus Corporation) and Shell-Guard (Perma-Chink Systems) are glycol-based borate products. Both products are easy to apply with a paint roller or garden sprayer. Timbor, also from Nisus Corporation, is a pure borate powder without any glycol additive. Timbor is mixed with water to apply. Some studies indicate that glycol helps to carry the borate into the wood, other studies found no difference.

All borate products should be applied before wood is stained and sealed for best results. Bora Care is a 40% solution whereas Shell-Guard is a 25.3% solution. Keep this difference in mind when comparing costs. Timbor is cheaper than either of the glycol-based borates but does not have the possible benefits of the glycol penetrant.

Borate solution should be applied to the unfinished back and to the tongue and groove edges with a small brush or paint roller. Apply solution to the top only if it is unfinished. After the solution dries the wood will be impregnated with borate which will prevent beetle larvae from boring into the underside, or edges, once the floor is installed.

Don't get the wood too wet as the flooring may warp. And, allow it to dry completely before installation. This procedure won't stop beetles already in the wood floor from emerging but it will prevent new attacks.

Treating active beetle infestations in wood flooring after installation -- For infestations in existing floors you'll need to first determine if the infestation is active (see discussion above). If it is active then look at this article for treatment suggestions.