<p>Thermal tolerance influences the survival, performance, and distribution of ectothermic organisms. Its effects are especially important given the advent of rapid climate change. While diet quality has been shown to modulate critical thermal maxima (CT_max) in ants under laboratory conditions, it remains unclear whether this response and the speed at which it appears are the same in wild ants. Here, we tested whether a carbohydrate-enriched diet could quickly increase CT_max in <i>Dorymyrmex thoracicus</i>, a heat-tolerant ant species in the Brazilian Caatinga. Using two field-based experiments, we found that ants given access to a 20% sucrose solution exhibited significantly higher CT_max values than did ants who did not have access to the sucrose solution. The second experiment showed that this difference appeared a few hours after the treatment, suggesting the operation of rapid physiological responses potentially linked to energy availability and heat shock protein synthesis. Thus, carbohydrate intake can immediately modulate thermal tolerance under natural conditions, a result that can help us predict how ants, and other ectotherms, may respond to climate-driven shifts in food availability and thermal stress.</p>