There are two major groups of termites, the wood dwellers (family Hodotermitidae) and the soil dwellers (family Rhinotermitidae). The latter cause over $250 million loss per year in the United States alone. The Formosan termite, a more aggressive species than the U.S. species, was discovered in the United States in 1965 along the Gulf and in Atlantic port cities. Soil dwellers attack only wood that is in contact with the ground or close enough to be reached through enclosed earthen runways, which are connected to the termite's underground galleries. Treatment of soil, use of treated wood, or shielding with metal and concrete are among the methods used to prevent entry of termites into buildings. Drywood termites do not require as high a humidity as do soil dwellers and will attack trees, fence posts, stumps, and wooden buildings.