A new Canadian butterfly species has been discovered: meet the Curiously Isolated Hairstreak
- Natasha Dudek
- May 2
- 3 min read
A new species of butterfly has been identified in Waterton Lakes National Park, Alberta. Named the Curiously Isolated Hairstreak (Satyrium curiosolus), its moniker reflects the species’ unusual geographical distribution and ecological isolation.
Once thought to be part of the Half-moon Hairstreak (Satyrium semiluna) butterfly species, this Alberta population has now been recognized as a completely separate species. The discovery came as scientists began reassessing the conservation status of the Half-moon Hairstreak in Canada. It’s currently listed as Endangered under the federal Species at Risk Act, but there has been growing momentum to downlist it to Threatened.
Why? Most Canadian Half-moon Hairstreak populations live in southern British Columbia (B.C.) and are closely connected to larger populations in the United States, where the butterfly is considered “apparently secure.” Given that there is little genetic or ecological distinction between the B.C. and U.S. groups, some experts argue that Canada’s conservation assessment may be more reflective of political borders than actual biological risk.
For the one population living in Alberta, however, the situation is dramatically different. Isolated by over 400 kilometers and occupying a unique environment, a team of researchers led from the University of Alberta realized that this population is genetically distinct, ecologically specialized, and shows no evidence of mixing with other groups. Notably, its known range is limited to just 300 hectares within Waterton Lakes National Park, with an area smaller than many city parks. Due to its small size and vulnerability, scientists have recommended upgrading this population’s status to Critically Endangered, the highest level of conservation concern.
Targeted conservation efforts for this population have been proposed. With very low genetic diversity and limited ability to adapt to rapid environmental change, one possible solution is genetic rescue, which consists of introducing individuals from other populations to increase genetic variation. But would that actually help?
To find out, researchers created the first full genome for the species and compared butterflies from Alberta, BC, and Montana. What they found was striking: the Alberta population has been isolated for around 40,000 years, with no recent gene flow. It also occupies a distinct habitat, has unique host plant preferences, and relies on a specialized mutualism with local Lasius ponderosae ants. These ants protect and care for the larvae, even allowing them to pupate in their underground nests, where they stay cool during heatwaves. In return, the larvae provide the ants with sweet secretions called honeydew.
Taken together, these genetic, ecological, and behavioral differences led researchers to conclude that this isn’t just a unique population of the Half-moon Hairstreak; it’s a separate species altogether.
As for genetic rescue? While it’s often a go-to strategy for struggling populations, in this case, it may do more harm than good, at least for now. The Curiously Isolated Hairstreak appears to have purged many harmful mutations over its long isolation (otherwise interbreeding would have caused some serious issues), and introducing new genes could re-introduce harmful mutations. Assuming they can even interbreed with their closest relative, the Alberta group lives in environmental conditions very different from other Hairstreak butterflies, raising the risk of outbreeding depression, where hybrid offspring are less fit. Hybridization with the Half-moon Hairstreak could disrupt the Curiously Isolated Hairstreak’s finely tuned local adaptations, for example its symbiotic relationship with ants.
Still, things could change. The Alberta population’s lack of genetic diversity could become a significant vulnerability, limiting its ability to adapt to the environmental shifts brought on by climate change. Scientists recommend preparing for that possibility now, by conducting controlled crosses to test reproductive compatibility and offspring health, in case future intervention becomes necessary.
In the meantime, this discovery highlights just how much there is still to uncover in the natural world. The Curiously Isolated Hairstreak, with its incredibly limited 300-hectare range, is amongst the most geographically restricted butterfly species known. It’s not just a fascinating scientific breakthrough; it’s a reminder of the hidden biodiversity that’s still out there, waiting to be explored.
Study:
MacDonald, Z.G., et al. " Genomic and ecological divergence support recognition of a new species of endangered Satyrium butterfly (Lepidoptera, Lycaenidae)." ZooKeys 1234 (2025): 291.
