Variation in thermal tolerance of North American ants

• Critical thermal maxima of 92 ant colonies was measured in this study.
• Within and among colony variation are important variables in studies of ant thermal physiology.
• Critical thermal maxima differed among ant species and was negatively correlated with body mass.

Changing climates are predicted to alter the distribution of thermal niches. Small ectotherms such as ants may be particularly vulnerable to heat injury and death. We quantified the critical thermal maxima of 92 ant colonies representing 14 common temperate ant species. The mean CTmax for all measured ants was 47.8 °C (±0.27; range=40.2–51.2 °C), and within-colony variation was lower than among-colony variation. Critical thermal maxima differed among species and were negatively correlated with body size. Results of this study illustrate the importance of accounting for mass, among and within colony variation, and interspecific differences in diel activity patterns, which are often neglected in studies of ant thermal physiology.