<p>Increased thermal stress is predicted due to climate change. While heat stress has well-known effects on physiology and ecology, understanding how heat stress affects organismal behavior is also important, as research in organismal biology shows that behavior links organism-level traits like respiratory physiology with ecological processes like food web function. Mantis shrimp (Stomatopoda: Crustacea) are important marine predators and sources of food for non-human and human animals alike. We studied the effects of acute heat stress on ecologically relevant behaviors in two species of mantis shrimp from disparate regions: the Indo-Pacific (<i>Gonodactylus childi</i>) and the Caribbean (<i>Neogonodactylus oerstedii</i>). While thermal data showed that <i>N. oerstedii</i> faces higher maximum temperatures and greater thermal variability than <i>G. childi</i>, including sea surface temperatures over 38&#xa0;°C (100&#xa0;°F), <i>N. oerstedii</i> was less tolerant of increased temperatures. Thermal stress led to changes in ventilatory behavior, which varied with body size and species identity. Further, as temperature increased, both species decreased their likelihood of striking—an important prey capture and predator defense behavior—but this decrease was more pronounced in <i>N. oerstedii</i> than in <i>G. childi</i>. Finally, in both species, larger individuals were less likely to stay inside their protective “burrows” than smaller individuals, especially as temperatures increased. Our data show how heat stress leads to complex behavioral variation in ways that may affect the role mantis shrimp play in marine ecosystems. We suggest future approaches to more closely link climate-related changes in organismal behavior with their physiological mechanisms and ecological implications.</p>