Good Natured: A real weasel, a bona fide mustelid

So the other day we had a bit of an oddball show up here at the ‘Knolls. Slinky and furtive, he skulked in the shadows and did his best to avoid detection. Frankly, he probably would have gone unnoticed, were it not for the sharp eyes of our coworker Greg Pipis.

Being the quick-thinking sort, Greg (who also was a participant in the monster buck incident a few weeks ago) recognized just what he was dealing with. Rather than confront the individual, and risk undue harm, he reacted exactly as any modern, smartphone-carrying naturalist would: He snapped a picture and texted it to me.

In a little twist of irony, I was just leaving a seminar about how to handle building intruders when I got the message. I enlarged the photo and analyzed the stranger’s unusual features. Small head. Tiny ears. Dark, beady eyes. Let me tell you, this guy was a real weasel.

A bona fide mustelid.

Mustelidae is the largest family within the order Carnivora. This diverse group includes 56 species in 22 genera and runs the gamut from otters, badgers and wolverines on down to mink and, yes, weasels. Here in Kane County, we have two species of weasel, the long-tailed weasel, Mustela frenata, and the least weasel, M. nivalis. Although the latter, littler one is considered to be more unusual, it’s the one we seem to encounter the most in our adventures in and around the Hickory Knolls Nature Area. Since Greg estimated the weasel he spotted to be about 8 inches long, we’re almost positive it was a least weasel. Last spring, I saw one ducking in and out of the crevices of a rock pile, and our basement chest freezer (aka The Freezer O’ Fun) holds the remains of not one but two M. nivalis.

(For us to have been completely positive of this most recent weasel sighting, Greg would have needed to see the animal’s tail. On long-tailed weasels, the appendage measures anywhere from 3 to 6 inches long and has a black tip; on least weasels, the tail is about 1 inch long, with no black tip.) Regardless of species, our weasel neighbors are renowned for one trait in particular.

These slender, sinewy creatures are such efficient predators, they often are regarded as killing machines. Long-tailed weasels, which range in size from 11 inches (small female) to 16 inches (large male) in length can consume prey as large as chipmunks, squirrels and rabbits. Least weasels, with a size range of 8 to 10 inches in length, specialize in smaller prey like mice and voles.

With their sharp teeth and lightning-fast movements, weasels make quick work of their intended meals, typically applying a few swift bites to the base of the skull or, sometimes, the trachea. During times when prey is abundant, weasels are known to cache food, ostensibly saving it for later. But since these meals are meaty, their "shelf life" is limited; they're also why finding lots of flies around the opening of a small burrow is a good clue that the home belongs to a weasel. This tendency to take more than can be consumed at one time has led to weasels' reputation as being wanton killers. In truth, their hunting prowess comes more out of necessity than anything else. The combination of a high metabolism and small stomach means these carnivores need to eat the same way Chicagoans vote – early and often. In fact, on average a weasel will consume 50 percent of its body weight in prey each day, and even more during the cold-weather months.

• Pam Erickson Otto is the manager of nature programs and interpretive services at the Hickory Knolls Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346 or potto@stcparks.org.