Under global warming, animal species show shrinking body size responses to heat, cascading into deep changes in community structure and ecosystem functions. Although the exact physiological mechanism behind this phenomenon remains unsolved, smaller individuals are expected to benefit from warming climate conditions more than larger ones.

Heat-coma, a physiological state with severe consequences on locomotion ability, is often considered an “ecological death” scenario under which individuals are unable to escape and are exposed to predation, further heat injury, and other hazards. Species are expected to increasingly encounter heat-coma temperature thresholds under warming, and body size may be an important trait for thermoregulation in particular for ectotherms. The relationship between heat-coma and shrinking body size, however, remains unclear. Yet, recovery after short-term heat-coma is possible, and little is known about its importance in thermal adaptation and how organismal size changes respond to post heat-coma recovery.

Here, we used ants, a classic model in ecophysiology, and first set an in situ experiment to examine the fate of heat-comatose individuals under field conditions to understand associated benefits of post heat-coma recovery. Then we quantified ants’ recovery ability after heat-coma using a coma-inducing dynamic thermal assay and asked if thermal resilience varies between species with different body mass.

Our results confirm that heat-coma represents an inherent ecological death with recovery after heat coma limiting predator capture. Additionally, following phylogenetic signals inclusion, organisms with small mass were more likely to recover, supporting the temperature-size rule and of recent studies supporting a decrease in body size composition of ectotherm community under warmer climatic conditions. Body size as a fundamental trait in ecology thus affects ectotherm survival in extreme hot conditions, with our findings suggesting how temperature stress could ultimately affect species' body size and community composition.