Subterranean termites form colonies and forage for wood in soil, which provides moisture and protection from extreme temperatures. As a result, subterranean termites are more widespread than drywood termites, which are more vulnerable to extreme cold. Also unlike drywood termites, subterranean termites don’t live in the wood they’re eating. Since their colony size is not limited by wood, one subterranean termite colony can cause more structural damage than one drywood termite colony. Although subterranean termites occur in every state except Alaska, structural infestations are more common in warmer climates. Subterranean termites are limited by frozen topsoil in areas where winters are extremely cold, reducing the overall number of structural infestations in these areas.
Most structure-infesting subterranean termites in North America are native species. The Formosan subterranean termite is an introduced species native to southern China. It is the most widely distributed and economically important subterranean termite in the world, although its distribution in the United States is mostly limited to southeastern states and Hawaii. Formosan subterranean termites can cause more structural damage in less time due to their high reproductive capacity, which produces colonies ten times the size produced by native subterranean termites. Formosans and native subterranean termites can be differentiated by looking at alate forewings under magnification. In general, subterranean termites have two heavy veins and no cross veins along the top margin of the wing. Formosan wings are also covered with fine hairs, giving them a velvety appearance.
Conventional liquid termiticides provide chemical barriers to subterranean termites underneath and/or around structures. They are the fastest and most economical management method that should last at least five years. Although termites tend to avoid repellent formulations, they can exploit treatment gaps and may find a way into treated structures. Non-repellent formulations do more than act as a barrier because termites will walk through treated areas and pick up a lethal dose that can be shared with the rest of the colony.