Besting the Bug: Termite Tips From FPL

Aside from a few areas, in Wisconsin, thanks to the long, cold winters, termites haven’t presented too many problems. That doesn’t stop researchers from the Forest Products Laboratory (FPL) in Madison, Wisconsin, from researching the best methods of termite control and eradication. Today, FPL employees are working on sophisticated methods of pest control, but here are a few tried-and-true tips from FPL’s Wood Handbook.


Termites, viewed under magnification in a laboratory setting. Notice the winged termites that can easily be mistaken for “flying ants”

About 56 species of termites are known in the United States, but they can be grouped into two categories: ground-inhabiting (subterranean) termites and wood-inhabiting (non-subterranean) termites.

Subterranean termites are responsible for most of the damage to wood in the United States, particularly in the South. The hazard of infestation is the greatest beneath buildings without a full basement (i.e. a slab or crawl space) or in any substructure wood component close to the ground.

Subterranean termites will develop their colonies in the moist ground (termites need constant moisture from either the wood they eat or the ground that they nest in) and build tunnels through earth and around obstructions to reach their food source—your home.

In spring, the termites grow wings, fly for a short time, lose their wings, mate, and start new colonies. “Flying ants” can be an indication of a colony, but not all “flying ants” are termites, and so the insects in question should be carefully examined. Another telltale sign of termites are they earthen tubes they build over the surfaces of a foundation or other open area to reach a wood source. Be on the lookout for these little dirt “runways.”

The best protection for wood in areas where subterranean termites are prevalent is to prevent the insects from gaining entry into the building. During construction, make sure that foundations are made of concrete or pressure treated wood. If you use brick, stone or concrete block, only cement mortar should be used, as termites can dig through some types of mortar.

And the more concrete the better—it’s a good idea to cap the foundation with 4 inches of reinforced concrete, ensure any posts supporting floor girders are made of concrete, and ensure basement floors are made of concrete as well. Untreated posts in a basement should rest on concrete piers too.

With a crawl-space type of foundation, wood floor joists should be kept at least 18 inches (and girders 12 inches) from the earth, with a polyethylene vapor barrier covering exposed soil and extending partially up the foundation wall. This will help keep structural members dry. Above ground, gutters, downspouts, and proper grading should be used to keep water away from the structure.

Insecticides can, and should, also be used on soil before a slab is poured. Furthermore, insulation containing cellulose used as a filler in expansion joints should be impregnated with an approved chemical that is toxic to termites. Sealing the top 1/2 inch of the expansion joint with roofing-grade coal-tar pitch also provides effective protection from ground-nesting termites.

The principal method of controlling an existing infestation is to treat the soil adjacent to the foundation walls with a soil insecticide. Contact between the termite colony in the soil and the wood must be broken. You can also block the “runways” from the soil to the wood or repair leaks or drainage problems that keep the structure wet. In any case, professional consultation is required, and homeowners should contact a national pest control operator association.

Unlike superficial problems like mold or mildew, termites can severely weaken a wooden structure. Humans will always build structures where termites live, but by being termite-aware and practicing good construction habits, you stand a better chance of making sure that these pests don’t turn your home into their next lunch.