Beetles in Wood Floors

- Sometimes just "watchful waiting" is best -

Summary: Hardwood floors that shows signs of an active beetle infestation such as emergence holes and boring dust can be disturbing to homeowners, to say the least! Treating the infestation can be difficult and expensive so sometimes the best approach is no treatment at all.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

Hardwood (oak, maple, bamboo, and so forth) floors may show signs of insect infestation sometime after the floor is installed. The first signs of infestation are small (1/16") holes that appear in the surface (see Beetles & Hardwood Floors for pictures) often accompanied by fine boring dust. Holes can start to appear immediately after installation or several years may pass before they are first noticed. The holes mark sites where powderpost beetles (see photo right) have emerged after developing in the wood for many months or even years.

lyctid powderpost beetle

lyctid powderpost beetle, adult (~ 1/8" long)

Powderpost beetles are one of the few wood boring insects that are able to re-infest seasoned and milled wood. This is important because it is this "cycle of infestation" that causes significant structural damage over time.

It is very difficult to control powderpost beetle larvae** (see A Picture of a Lyctid Powderpost Beetle Larva) once they have burrowed into the wood. It is far easier to prevent new infestations than to treat existing infestations. This is why new floor installations should be treated with borate (see below). However, there are some things you can do if faced with an existing floor that is infested with powderpost beetles.

** also called woodworms

Treating active beetle infestations

New damage occurs slowly so you have time to make good decisions. It is possible that a small infestation will "burn itself out" and no new emergence holes will occur after a few years. In this case very little structural damage will probably occur. A few holes can be considered "patina" or they can be patched the next time the floor is refinished.

Large infestations, however, can cause significant damage to the internal structure of the flooring that may actually lead to failure of the floor surface. If the surface fails, infested sections of the floor will need to be replaced. In addition to floor damage, emerging beetles may infest other, unfinished hardwood (oak, maple, ash), in the home. Softwood (Douglas fir, fir, pine) used for structural framing is generally not affected by beetles that emerge from hardwoods.

There are several different approaches to managing an existing infestation. Many times simple "watchful waiting" is the best approach. Mark existing emergence holes with a grease pencil so you can track new holes if they occur. You may find that the infestation stops on its own or is so slow that no repair is needed.

Another option is to sand the floor down to bare wood, apply a solution of borate insecticide, such as Timbor or Bora Care, then refinish the surface. There is some evidence that this surface treatment will control any beetle larvae within about 1/4" of the surface. Adults emerging through the treated surface will die. This treatment, however, does not eliminate larvae that are deeper but it still makes sense if the floor will be refinished anyway.

The most expensive approach is to "tent and fumigate" the home (see What is Structure Fumigation?). This involves placing a tent over the home so that an insecticidal gas, or hot air, can be pumped in. If done correctly the treatment usually eliminates the infestation. However, tenting and fumigating is very expensive and must be performed by an experienced pest control firm. In the end you must balance the cost of treatment with the costs of potential repairs down the road. My own first choice is always "watchful waiting" and prepare to replace flooring if serious damage occurs.

With any approach you should obtain some flooring pieces from the manufacturer in the event that a section of the floor surface fails and needs to be replaced. Depending on circumstances you may also try to secure funds from the manufacturer to pay for repair labor, since the floor was likely infested when it was installed.

Related Articles

A List of Insects That Damage Wood

What is Timbor Insecticide?

What are Bora Care & Shell-Guard?

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