The Carlisle Mosquito Online

Friday, May 27, 2005



Name: This week's critter is the animal formerly known as the short-tailed weasel. It is now known as the ermine. The scientific name is Mustela erminea. It is also called a stoat, mainly by the Brits. The long-tailed weasel is still called a weasel and so is a "treacherous or sneaky person" according to the American Heritage Dictionary.

When and where seen: On May 9, Jean Keskulla saw an ermine going into a wood-pile in her yard on Concord Street. Ermine are largely nocturnal but are known to come out during daylight hours.

The long and the short of it: The ermine has a long body but a short tail; it has a long neck but short legs. Only on average is it well proportioned, like my dachshund. By April, the ermine has completed its spring molt and the white winter coat is replaced by soft dark brown fur on its upper parts, with slightly darker brown on the head and legs. The feet and the underparts stay white all year round. The terminal third of the tail stays black all year round. The spring molt has been shown to be triggered by the length of daylight rather than by temperature — else Jean's ermine might still be white.

Not so weasily distinguished: Ermine are similar in shape and color to the long-tailed weasel so the overall size and the length of the tail are the main differentiators. But it gets complicated — in both species the males are larger than the females so a large male ermine would be about the same size as a small female long-tailed weasel. Ermine are 7 to 13 inches long, not counting the tail and weigh up to 7 ounces. Long-tailed weasels are 11 to 22 inches long, not counting the tail, and weigh up to l2 ounces. The animal Jean saw was about a foot long including the tail and so it can be identified fairly safely as a female ermine. A male ermine would be harder to be sure about.

Behavior: Ermine are active throughout the year and are mostly nocturnal. They are solitary creatures and get together only in the breeding season. They are bold, alert, and curious. While they are able to swim and can climb trees, they are primarily terrestrial. The normal gait is a kind of bounding or loping movement. They are energetic, cunning, clever, fearless hunters. They will quickly retreat when surprised but will reappear in response to a mouse-like squeak. D'Ann Brownrigg has a story of being out on a birding walk and making chirpy bird-like noises only to find the group was being followed by an ermine.

Diet: Ermine are carnivores. They kill more than they can eat but are not wasteful. They consume the flesh, fur, feathers, bones and all, and they cache the reserves. The dietary model would be the pyramid at Giza. Big is good, and it is important to have tunnels and safe places to store excess food. The "eat most" base level of the pyramid would be mice and voles; the next level would be chipmunks and animals larger than themselves like cottontails; after that it would be frogs, lizards, snakes, birds, and insects; the final level, "eat least and only if you have to," would be carrion. Ermine have a high metabolism and burn through a quantity of food equivalent to one third of their body weight per day. They don't get many miles per mouse. They have evolved as very efficient predators.

References: Alfred J. Godin, Wild Mammals of New England; Donald & Lillian Stokes, Guide to Animal Tracking and Behavior; Richard M. DeGraaf & Mariko Yamasaki, New England Wildlife.

2005 The Carlisle Mosquito