The fearless weasel’s white winter fur is a blessing and a curse

When it comes to disappearing into winter landscapes, Minnesota’s weasels boast a distinct advantage. Like snow hares, they shed their brown summer fur for a snow-white coat.

This survival adaptation, called leucism, helps them evade predators such as foxes, cats, hawks, owls and even other weasels, while their agility and stealth help them capture mice, voles and small birds.

“They can fit into about any hole a mouse or vole can get into,” said Blane Klemek, regional wildlife manager with the Department of Natural Resources’ Northwest Region. “They’re fascinating creatures and absolutely fearless.”

Three species of weasels make their home in Minnesota. The largest one, the long-tailed weasel, weighs about 7 ounces and can be 16 inches in length. The short-tailed weasel, also known as ermine or a stoat, can be 7 to 14 inches long and weigh 2 to 5 ounces. Both species have tails tipped with black fur.

Weasels’ white winter fur, especially that of ermine, were historically coveted as trim for luxurious capes and coats. The white fur was considered a sign of purity in medieval times when it was sewn on the robes of monarchs and high clergy. It also embellishes Britain’s Robe of State, which was worn by King Charles during his 2023 coronation.

North America’s third weasel species, the least weasel, lacks a black-tipped tail and clocks in at only 6 to 7.5 inches long and weighs 2 ounces or less. It’s listed as a rare species in Minnesota, partly due to competition from other weasels.

The least weasel has another potential disadvantage: its fur glows under ultraviolet light. It’s possible that makes it more vulnerable to predators such as kestrels and red-tailed hawks, which have UV vision. The raptors can find rodents, as well, by following the UV glow of their urine trails in ditches and fields.