<p>In the face of the current biodiversity crisis, understanding the species biology of organisms most threatened with extinction is more important than ever. Endemic to Canada’s Waterton Lakes National Park, the Curiously Isolated Hairstreak butterfly is the most geographically restricted butterfly species currently recognized (&lt; 3 km² global range). Although this population has been known for decades, it was only recently described as a distinct species. Very little is known about the species biology of the Curiously Isolated Hairstreak, and published information is scattered and incomplete. An exhaustive compilation of all known species biology information is needed for this species, to facilitate further research and conservation planning. Most existing information on this species was obtained via a variety of surveys, both structured and unstructured, during the months of May through August in 2021–2025. From these, we provide detailed descriptions of the morphology (including egg, larval, and pupal stages, and fluorescent properties under 365&#xa0;nm UV light), and comprehensive information on the currently known phenology, food plant preferences, behavior, dispersal ability, and natural enemies of the Curiously Isolated Hairstreak. We confirm that the Curiously Isolated Hairstreak exhibits distinct resource preferences compared to related species, and has unique dispersal behavior. This makes it a fascinating case-study for speciation, and offers a rare opportunity to feasibly study an insect species over its entire geographic range.</p>