An isolated population of the red imported fire ant,Solenopsis invictaBuren, was discovered in Lubbock, TX, during August 1985. This find represented the northwesternmost known population in North America, and it had survived since at least 1983. Preceding the 1985–1986 winter, 207 colonies were located and marked, and 85.4% of the colonies survived until the following spring. Of 277 colonies located before the 1986–1987 winter, 47.8% survived until March 1987. Colonies found near brick walls and roadside, concrete curbs were 89.5 and 80.2%, respectively, of the numbers found at the same locations the previous fall. These percentages are significantly greater than those of colonies found in open, more exposed areas (40.0%). The larger number of overwintering colonies found near human-made structures may have been the result of colony survival due to greater insolation and consequently warmer soil temperatures than those in open areas. However, the larger number of surviving colonies could have been a manifestation of location preference resulting from repeated colony movements. Only after persistent and aggressive intervention through the use of insecticides was the population eliminated.