With two thirds of the total annual infestation control bill spent on this insect alone, termites are by far the most economically important pest plaguing wood structures. Though more than 50 species of termites live in the U.S., about 95% of all damage is done by subterranean termites, which nest underground. Other termites of local significance include drywood termites found along America's southern border from California to Florida, dampwood termites of the coastal Pacific Northwest, and a recent exotic arrival in several Gulf states, the Formosan termite. Lacking the natural antifreeze of other insects, subterranean termites cannot hibernate during freezing weather and must remain active year-round. Concentrated in the Southeast, they have expanded northward only since the early 1900s with the widespread adoption of central heating.