Insects possess several physiological and morphological adaptations to high temperatures; in particular, critical thermal maxima may be of increasing importance as climates warm. We sought to determine the relationship between critical thermal maxima and body size in red imported fire ants, Solenopsis invicta. Thermal maxima were measured and regressed against body mass, tibial length, head width including the eyes, and total body length in individuals from 35 fire ant colonies within and around Lubbock, Texas. Major and media workers survived higher temperatures more often than did minor workers. This may relate to surface-area-to-volume ratios, higher desiccation resistance in larger workers, or both; however, further studies are needed to confirm this. These results suggest that body size may be an important predictor of thermal performance for ectotherms.