The acute stress response is a cornerstone of animal behavior research, but little is currently understood about how responses to acute stressors (i.e. discrete noxious stimuli) may be altered in future climates. As climate change ensues, animals may experience chronic stress due to persistent warmer temperatures and environmental conditions altered by weather extremes, such as wildfires and storms, which are expected to increase in frequency and intensity. This chronic stress has the potential to cause changes in animal responses to acute stress, but whether such changes occur is unclear. Here, we investigated whether new environmental conditions caused by wildfire affected the fight-or-flight component of the acute stress response of a widespread social insect. We compared thatch ant (Formica obscuripes) behavior in neighboring sagebrush steppe areas that were unburned or burned three months prior. As predicted, we found that ant workers primarily defended their colonies by attacking a threatening stimulus, but ants in the burned environment were more likely to flee from the stimulus. While causal mechanisms require further study, these findings suggest that ant workers provide less protection for their colonies following wildfire, which may increase individual worker survival but make colonies more vulnerable to antagonists. As chronic stress due to wildfires and other shifting climatic variables becomes more widespread, understanding changes in animal responses to acute stressors will be crucial for anticipating animal survival in the Anthropocene. We suggest several research priorities for work on stress-related animal behaviors in environments altered by climate change, including greater focus on invertebrates.