If you have termites you very probably have subterranean termites. There are other kinds but, they're not nearly as common in the US. You'll have to check the links at the end of the page to learn about them. This discussion applies only to subterranean termites.  This page may help you tell which kind of termite you have, but it didn't seem too helpful to me.  If you decide you have drywood termites go here.

Subterranean termites live in underground colonies (nests), that maybe 5 to 10 feet below the surface. They're only about 1/8 inch long yet, the workers forage hundreds of feet, traveling underground,surfacing periodically, searching for food (wood) to feed the colony.

If they find the wood your house is built of they can do a lot of damage.

Termites frequently enter a housing structure near the first-floor level. It’s best to consult a qualified pest-control company to make sure the necessary treatment is provided. The best companies give a lifetime guarantee on their work that will cover repairs if insect damages eventually result. Construction design precautions include, on a hollow-block foundation, filling the top courses of block with concrete, and installing a metal termite shield along the foundation wall. Such a shield must be made of noncorroding metal and must be installed so no gaps exist along seams or where the shield is attached. This continuous strip of thin metal, attached between the foundation and sill plate, should extend at least 2 inches out and 2 inches down from the foundation wall, bent downward at a 45-degree angle.