Small, white and feisty least weasels

Chel Anderson is a botanist and plant ecologist. She lives here in Cook County and joins us periodically to talk about phenology or what’s going on in the woods right now. Welcome, Chel.

Anderson: Hi!

Well, they’re white and pretty ferocious hunters. So, tell us about least weasels.

Anderson: OK. Will do. Least weasels. Let’s start out with some basic things about weasels, because it’s easy to get them confused, I think. We have a group of little weasels, and the least weasel is, of course, the smallest followed by the next largest, which is the ermine. They are different. Some people confuse them. And then, the next largest—so the largest of the weasels—is the long-tailed weasel. So, we’re going to talk about the least weasel, which, as you say, is a very notoriously ferocious and feisty predator of the woods and meadows and fields of a fairly large range of North America. We’re kind of in the southern half of its range, so it goes all the way up into the arctic. So, it’s a pretty successful little carnivore, but a hard one to get a look at because they’re quick, they’re small, they’re really busy because they are hunting pretty much 90 percent of their lives, which are pretty short. They live about a year, is all. So, it’s a fast- and furious-paced life for a least weasel. Least weasels are 6.5 to 8.5 inches long and about a quarter of that is the length of their little, short tail. So, these are really small creatures. Sleek, long and sleek, and chocolate brown on the back and tail in the summer and white on the chest and belly in the summer. Then, turning all white like the ermine in the winter.

Do all weasels turn white?

Anderson: No, the long-tailed weasel does not turn white. The ermine and the least weasel do. The key distinguishing feature—both summer and winter, but especially obvious in the winter between the least weasel and the ermine—is that the ermine has a black tip on its short tail. The least weasel does not have a black tip.

Well, how do these guys survive in the winter?

Anderson: Yeah, well, the least weasel is eating between a third and a half of its body weight every day. So, think about trying to do that yourself.

No, I’d really rather not think about doing that. I wouldn’t be able to get in the studio.

Anderson: No, but it would take a lot of time, right? Even though getting food is a little bit easier for us, you know, even if you have to go somewhere and go shopping for it and prepare it. It’s still fairly easy. But, if you have to hunt for your food, this is a big endeavor to eat that much of yourself. A least weasel weighs one to maybe 2.5 ounces, so this is less than you can mail with a first-class stamp. So, they are small, but still, eating half your body weight is going to suck up a lot of time and they pack a lot of energy and feistiness in that little package that they are. This time of year, they are spending a lot of time searching, and they use kind of random search pattern for their hunting method. And they are checking out every little tunnel down into the snow, every little tree well that will eventually develop. They are using both visual, auditory and scent clues to know whether they should explore further when they poke, you know, their heads down a dark hole. And, of course, they’re small enough to be able to go down into that subnivian layer and move around down there. Even though, of course, it’s going to be quite dim, they’re going to be able to move around and search for their prey in that subnivian layer and take advantage of those better temperature conditions. Because, remember, like all of our critters, they’re living in this energy budget world in the winter and they need to be able to sustain their body temperature in the face of the cold, so if they can get down and spend some time in the subnivian and have it pay off in terms of finding some food, then you’re having a better chance of sticking within that energy budget.

What are they going to find down there?

Anderson: Well, their big items are going to be rodents of all kinds—mice, shrews, voles. They might even find the occasional insect that’s dormant, and they would eat those, and in the summer, they eat insects as well as if they happen into ground-nesting birds, small ground-nesting birds, they would definitely take advantage of those options. They’re very efficient and effective predators. They are ferocious as you said, in the face of especially something—another animal, including a person—trying to take away a kill, they will go on the offensive against much larger animals in defense of a kill that they’ve made. But, because of their size and, of course, because they are important players in the lower part of the food chain, they’re a great meal themselves, so they are actively hunted by larger mammals, fox, even larger weasels like the ermine or the long-tailed weasel. House cats, even, have been known to take least weasels, and then raptors, of course-- owls and goshawks. If you want to try to see evidence of them, because they’re really hard to see in the summertime, as a lot of our other smaller animals, winter is a good time to try to pick out their tracks from among the variety of tracks that are out there. So, if you want to try to check that out, recall that weasels are bounders, so you’re looking for pairs or small clumps of tracks that are separated by long leaps. And, in the case of the least weasel, we’re talking about the leaps that aren’t maybe more than 8 inches, and that would probably be the outside. And, they’re going to have very tiny groups of tracks because their feet are only about a half an inch in length and width. These are weasels that might leave a bit of a body drag because they have such short little legs, if the snow is really light and fluffy, they’re going to go down. You know, you might be lucky enough to spot one zooming across the surface of the white snow. But, if it has a black tip, don’t be misled.

So, that’s the most we can say about the least.

Anderson: Perfect.

Chel Anderson, botanist and plant ecologist. Thanks for helping us understand what’s going on with least weasels this winter.

Anderson: You’re welcome.