Meet Your Neighbors

Weasels:
Small, Elusive Predators

Two species of weasels occur in the Chicago Wilderness: the least weasel, Mustela nivalis, and the long-tailed weasel, Mustela frenata. Though the long-tailed weasel is the most widespread carnivore in the Western Hemisphere, the chance of coming across either species in the wild is practically nil. Nonetheless, I’ve been lucky to meet six weasels over the past 30 years. It hasn’t been due to any skill on my part — it turns out that our family homestead of more than 150 years in a tiny corner of Kane County is prime weasel territory.

Weasels are hard to confuse with other mammals. They are much smaller and thinner than mink or otter, the only other local creatures with which they might be mistaken. In Illinois, the least weasel is found only in the northern half of the state, while the long-tailed weasel occurs throughout. As its name suggests, the least weasel is small, generally less than half the size of the long-tailed weasel. Adult least weasels are about seven to nine inches long and weigh no more than two ounces, making them the smallest carnivores in the state. Their long-tailed cousins are 12 to 16 inches long and weigh between three and ten ounces. Since the sizes of individuals of these two species can be close, however, the best way to differentiate them is to look at their tails. Tails of least weasels are uniformly reddish brown and typically about an inch long, while those of long-tailed weasels have black tips and are several times as long, from three to six inches. Both species can turn completely white in winter, especially farther north where snow cover is more frequent.

The population and status in Illinois of both weasel species remain virtually unknown. Both species of this reclusive and furtive creature are considered rare. The long-tailed weasel appears on the Illinois watch list of potentially threatened or endangered species. Despite exhaustive efforts, researchers in Illinois and elsewhere have sometimes failed to locate even a single individual, let alone a population large enough to study. The best information we have about weasel population and distribution comes from the mostly inadvertent trapping of 60 or so weasels across the state each year.

Both species of weasel frequently prey on animals much larger than themselves, including rodents and rabbits. A favorite prey species of the long-tailed weasel in Illinois and elsewhere is the state-threatened Franklin’s ground squirrel. My grandfather tells of a time when Franklin’s ground squirrels were very abundant in our part of Kane County, but by the mid 1970s, these “gray gophers” had become scarce.

Three of my encounters with weasels resulted from my boyhood efforts to trap Norway rats on the Rohrsen family farm 30 years ago. I unintentionally caught two least weasels and one long-tailed weasel. Two of the weasels were carrying mice, each with the telltale bites that weasels typically administer to the base of the skull to quickly kill their prey.

This past year, I once again encountered weasels in virtually the same area I had as a boy — near the Rohrsen farm and in the small adjacent Rohrsen Prairie. Unfortunately, I found two long-tailed weasels dead on an intersecting road. Happily, a third offered me a unique and ample photographic opportunity. This weasel seemed almost as intrigued with me as I was with it, as I watched it jump from the prairie grass into a tree, where it studied me intently. After a productive photo session, we went our separate ways through the dropseed, fringed gentians, and prairie lettuce.

Although now seriously threatened by road development and agriculture practices, the Rohrsen Prairie today remains virtually unchanged from 30 years ago. In addition to offering habitat for weasels, the site and adjacent land support a successfully breeding pair of upland sandpipers. Such prairie remnants — even small ones — are critical to preserving threatened and endangered flora and fauna. Thinking back to my past, I hold out hope that weasels like the ones I encountered may still be stalking Franklin’s ground squirrels across the rolling hillsides there.

— Bill M. Strausberger