Distinct Species of Ermines Have Been Hiding in Plain Sight

Arguably the cutest member of the weasel family, ermines can be found throughout the northern regions of North America and Eurasia. A closer look at ermines suggests these creatures really represent three distinct species, in a discovery with ecological implications.

Sure, ermines look cute, but their slender bodies pack a mighty punch. Despite measuring anywhere from 6.7 to 13 inches (17 to 33 cm) in length, ermines—among the smallest of the weasels—are formidable hunters, preying on shrews, mice, rats, squirrels, and even the occasional rabbit, which is a wild thing to witness. Ermines, also known as stoats or short-tailed weasels, aren’t picky eaters, and they’re often found munching on bugs, worms, and berries.

Ermines feature a small face, short legs, oval ears, and a furry tail. Their coat is normally brown but turns a brilliant white during the winter, except for the tips of their tails, which remain black (southern populations don’t turn white in the winter). Native to North America and Eurasia, these adaptable mammals are comfortable in a variety of habitats, including forests, marshes, meadows, and open pastures.

Their scientific name is Mustela erminea, but as new research published in Diversity and Distributions argues, there are three species of ermines, not just one. That this might be the case is not a huge surprise, given that 34 different subspecies of ermines are known to exist. What’s more, some ermines have been trapped on islands for hundreds of thousands of years, resulting in the emergence of distinct characteristics, and as a result, distinct populations.

“Until this study there was only one recognized species of ermine—Mustela erminea—distributed throughout the Holarctic,” Jocelyn Colella, an evolutionary biologist at the University of Kansas and the first author of the new study, explained in an email. By “Holarctic,” Colella is referring to the northern regions of both Nearctic North America and Palearctic Eurasia.

For the study, Colella and her colleagues analyzed whole genome sequences of ermines described in an earlier paper (DNA was analyzed from specimens found across North America, Europe, and Asia), followed by a physical analysis of skulls belonging to 27 subspecies.

Analysis of this data pointed to the presence of three distinct species, with the Mustela erminea complex being divided into three proposed species: Mustela erminea from Eurasia (which includes 18 subspecies), Mustela richardsonii found in continental North America (with 13 subspecies), and Mustela haidarum from the Haida Gwaii Archipelago of British Columbia and Prince of Wales Island in Southeast Alaska (three subspecies). Of the 34 subspecies, 12 still require additional study, according to the paper.

Of the three newly described species, M. haidarum is probably the most fascinating. These ermines “appear to be the result of an ancient hybridization event between the two [other newly proposed] species, followed by extended isolation in a glacial refuge and now on an island,” said Colella. This population became stranded on their respective islands around 375,000 years ago, and they’ve been on their own evolutionary journeys ever since, according to the research.

The authors believe their new findings should inform sensible conservation management strategies to protect the island species from threats like old-growth timber harvests, mining, and tourism. Diseases common to pets can also spread to ermines, and “the devastating reports of recent transmission of SARS‐CoV‐2 from humans to [weasels] are yet another potential conservation challenge,” write the authors. Indeed, massive culls of farmed mink took place last year, as fears grew that the coronavirus was mutating in them and spreading back to humans.

The new research suggests more unique species belonging to other animal groups are still waiting to be found, particularly on isolated islands. We just have to find them.