So called because they usually are coming from well-established colonies underground, which have a Queen, King, and many, many thousands of workers. There are numerous kinds of subterranean termites, the most damaging of which in the U.S. is the Formosan Termite. This species is common in Hawaii, well established in the Gulf Coast States, found in Southern California, but absent elsewhere, as it is a tropical species that does not do well in colder climates.
Subterranean Termites are the hardest to control, because there is no possible way to actually get to the below-ground colony to kill it, with the possible exception of new termite baits which may, over time, eliminate the colony. Termite baiting is discussed in a separate document. Except for the bait products, "control" of subterranean termites consists of modifying the structure to make access to the wooden parts as difficult as possible, and applying a chemical barrier on the soil, under the structure, which the termites cannot pass through, holding them away from the structure.
The Preferred Termite Environment
Movement by Subterranean Termites, once they leave their hidden galleries in the soil, always is within tubes of mud that they build, using their saliva to hold the bits of mud together. Usually these tubes are made against a solid surface, such as a foundation or pier post, but occasionally may simply rise from the ground and go directly into your subflooring as tubes referred to as "free-standing." Thus, the termites are alive and well below your home - or possibly in the neighbor's yard, or the woods out back - looking for other sources of food, but unable to use your house.
Those factors that assist these termites in their activities are:
- direct access to the wood, called "earth-to-wood contact," which must be separated
- excessive moisture, which helps them survive and work quickly
- excessive wooden debris in crawl spaces or outside the structure, allowing them local food that may draw higher numbers of workers to an area