Extreme environments often support rare and endemic species, but the adaptations that allow these organisms to persist there remain poorly understood. Because rare species are particularly vulnerable to environmental change, understanding their habitat preferences and physiological constraints is critical for effective management. We hypothesize that rare species inhabiting extreme thermal environments are experiencing physiological stress, but select for these habitats to avoid the greater biological diversity of less extreme ecosystems. Yellowstone National Park, the world’s first national park, hosts a variety of unique and extreme habitats. Our research focuses on the aquatic macroinvertebrate communities in the park’s 58 rock glaciers and >10,000 thermal features. To our knowledge, the ice-cold headwater streams draining rock glaciers have never been systemically surveyed, representing a major gap in our understanding of Yellowstone’s biodiversity. More studies have been conducted on Yellowstone’s thermal features, but none focused on aquatic insects. In 2025, we surveyed 33 sites near 14 rock glaciers to quantify used and available habitat across a broad temperature gradient. We also confirmed the status of streams draining rock glaciers as flowing or dry. Our focal species for these surveys is the Western Glacier Stonefly (Zapada glacier), a federally threatened insect in Wyoming and Montana. Zapada glacier likely occurs in Yellowstone based on proximity to other known populations, but they have never been surveyed there. Our samples confirm the presence of Zapada, but species-level identification requires pending DNA barcoding. Additionally, we investigated ~800 thermal features and conducted aquatic macroinvertebrate surveys at 51 suitable sites. We evaluated how community composition changed along a linear thermal gradient within each thermal outflow stream (i.e., distance from pool source). Future work will involve surveying additional rock glaciers and thermal features in Yellowstone. We will conduct in situ physiological experiments to test a mismatch between the fundamental and realized niche in each of these extreme environments. Our research will provide foundational data on the aquatic insect communities at both ends of Yellowstone’s thermal spectrum, ensuring the park’s biological diversity will be better understood and preserved.