Curiously Isolated Hairstreak: The Story of a Newly Recognized Species

When I first started working on what we thought was a regional population of halfmoon hairstreak in 2021, our team quickly realized there wasn’t a lot known about the butterfly.

We knew when and where it flew — between July and August on the Blakiston Fan in Waterton Lakes National Park — and that it was an isolated population. Beyond that, there were still major gaps in our understanding of its life history: we didn’t know what plant the larvae fed on, whether it had associations with ants (as many hairstreaks do), or why this population was so curiously isolated.

Working alongside a strong field team, we began piecing those answers together.

One of our first discoveries was that the Waterton hairstreak feeds on a different lupin and relies on a single ant species, unlike populations in British Columbia. Combined with the 450 km separating it from any other population, it was clear something didn’t line up.

So, we looked at the genetics.

When we ran the full genome analysis, everything came together. The data showed that this population had been isolated for around 40,000 years, surviving through multiple glacial periods without reconnecting with other populations.

At that point, it became clear this wasn’t just an isolated population or subspecies of the halfmoon hairstreak, but it was its own unique species, which we dubbed the curiously isolated hairstreak in 2025.

One of the most interesting discoveries was its relationship with ants. Unlike related species that partner with several ants, this hairstreak relies on just one — the Ponderosa meadow ant — which protects and shelters the caterpillars underground in exchange for nutrient-rich secretions. This level of specialization is remarkable, and often it’s easier to find the ants first, then the larvae sharing their habitat.

Despite having persisted for tens of thousands of years, this species is now considered Endangered. Its entire population exists within a single, small area, making it especially vulnerable. Invasive plants are reducing habitat quality, and any major natural disasters could have serious consequences.

That’s why the focus now is on strengthening the population. We’re monitoring habitat, managing invasive species, and beginning to bring individuals into human care so we can learn more and support future population growth.

For me, being part of this discovery has been incredibly exciting.

It’s rare to find a new species, and even more meaningful to be able to contribute to protecting it. There’s still a lot we don’t know, and that process of discovery is what drives this work forward.

This species has been here for thousands of years, largely unnoticed. Now that we know it’s here, we have the opportunity, and the responsibility, to make sure it continues. The site also plays a key role in preparing for the species’ future reintroduction into this historic range.