(1) We tested the thermal tolerance of red imported fire ants Solenopsis invicta in two small-scale habitats with different thermal microclimates. (2) Knock-down resistance indicated that colonies from an unshaded, warmer site had higher heat tolerance than colonies from a shaded, cooler site. This increased heat tolerance came at no apparent cost to cold tolerance, as ants from both habitats had similar chill-coma recovery times. (3) These results show a marked physiological response to localized anthropogenic habitat alterations. (4) Quantifying the adaptability of thermal tolerance could be important in understanding the ubiquity of fire ants in the southeastern United States. &