Termite size varies by species. Eastern subterranean termites, the most widely distributed in the country, are about three-eighths of an inch or 10 millimeters long. They can be found everywhere in the United States except for Alaska. Western subterranean termites, which are not as widely distributed, are about the same size, while dark southeastern subterranean termites are only about 7 to 8 millimeters in length.