Floodplains of gravel-bed rivers occur throughout the globe and are hotspots of biodiversity, maintained in part by their connectivity in longitudinal, lateral, and vertical dimensions. Below the surface, alluvial aquifers are vast and interconnected, supporting a unique community of both obligate and opportunistic fauna. Living in alluvial aquifers, aquifer stoneflies exhibit unique adaptations, including remarkable tolerance to hypoxia and anoxia. These adaptations allow them to exist as abundant consumers in aquifer food webs subsidized by ancient methane. However, living in alluvial aquifers, aquifer stoneflies are exposed to much more stable groundwater temperatures compared to benthic species in the river. The Climate Variability Hypothesis predicts that organisms exposed to more variable temperatures should evolve broader thermal tolerance limits. We predicted that benthic stoneflies would be less sensitive to warming temperatures because they are exposed to more variable river temperatures. We measured critical thermal maximum (CTMAX) and conducted intermittent respirometry experiments on nymphs of five benthic and three aquifer stonefly species to test their sensitivity to warming temperatures. CTMAX values of benthic taxa were ~ 5 ºC higher than those of aquifer taxa and varied among genera. In contrast, the thermal sensitivities of metabolic rates were surprisingly indistinguishable between benthic and aquifer taxa. During respirometry experiments benthic and aquifer taxa stopped moving (an indicator of stress) at similarly high temperatures and survived at similar rates. Differences in CTMAX suggest that benthic stoneflies may tolerate warming temperatures better than aquifer species, however metabolic responses were surprisingly similar for the two habitats. Regardless of having higher CTMAX responses, benthic taxa will also experience greater near-term mid-summer and midday temperatures as the climate warms. Assessing which group is more vulnerable therefore likely requires understanding relative rates of warming in the two habitats, which currently is poorly known. We call for more work on patterns of temperature change in a floodplain ecosystem context.