Rare animals are difficult to study, but understanding their habitat selection and comparative physiology is essential for conserving populations and promoting biodiversity. Extreme environments often have high proportions of rare, endemic species, but we challenge the assumption that they thrive there because they are physiologically adapted to the harsh conditions. The Narrow-foot Hygrotus Diving beetle (Hygrotus diversipes) is a rare beetle that occupies eight intermittent streams that experience the harsh environmental conditions of arid basins, including desiccation, flash floods, and extreme specific conductivity. This beetle is only known from Wyoming and has been repeatedly petitioned for protection under the US Endangered Species Act. We hypothesize H. diversipes are physiologically stressed in these streams, but they select them due to a competitive disadvantage in less harsh ecosystems. Our lab experiments found 70% of the beetles kept in 30mS/cm died after just five days, and ecological death occurred when individuals remained in 16mS/cm for 30 days. Despite this, Hygrotus diversipes have been detected in conductivities as high as 64mS/cm, and the highest conductivity we measured at a known site was 110mS/cm! Additionally, our models using projected precipitation and temperature values predicted an increase in salinity at known H. diversipes sites. Currently, we are investigating the species’ swimming and flying capabilities to understand the degree to which these beetles can leave unsuitable habitat. If this beetle is already living near its physiological limits, increases in conductivity due to anthropogenic water use and environmental change could lead to extirpation from known sites. Our results suggest that some rare species are not specialized to extreme conditions and they are instead living at the edge of their tolerance, making them especially vulnerable to habitat change.