If your familiarity with weasels only extends to your ability to hum along to the tune of "Pop goes the weasel," you're not alone. Weasels aren't exactly rare critters, but they are unfamiliar to most people because they are seldom seen even in places where they are common.

The world is home to 16 weasel species, and two live in Illinois: the long-tailed weasel, which lives across the state, and the least weasel, which is only found in the northern half of Illinois, according to Wildlife Illinois. A third weasel species, the short-tailed weasel, can be found in parts of the northern United States and much of Canada, but we don't see it in Illinois.

Least weasels are not often seen by humans even in areas where they are common, but long-tailed weasels are more common and familiar to people. Unlike most mammals, the color of all three weasel species is variable, changing with the seasons. They most commonly have brown fur on their backs, with white or cream-colored bellies, Outdoor Illinois reports. In the winter, weasels change color as a protective strategy, molting their brown fur for a lighter-colored coat to help them better blend in with their environment.

They may be nearly all white in color in areas where winters are snowy. While this molt is designed to help camouflage them in the winter months, it can actually have the opposite effect when little if any snow falls, the National Wildlife Federation reports. Against a drab and dreary winter background, their white fur stands out, drawing attention to themselves. 

This seasonal color change isn't unique to weasels, but most of the animals that undergo such a change are more closely associated with Arctic environments. Other animals that turn white in winter to better blend in include Arctic foxes; hare species including the snowshoe hare and Arctic hare; and the peary caribou, which lives exclusively in the Canadian Arctic archipelago, Live Science reports. 

Both our local weasel species have long, slim bodies and short legs, like a Daschund. They have wide heads and small, round ears. Long-tailed weasels are considerably larger than least weasels. They are about 11 inches to 17 inches long with tails about half the length of their bodies. Least weasels are generally no more than 10 inches long, and their tails are much shorter, only about a quarter of their body length, Wildlife Illinois reports.

Weasels are not strictly nocturnal or diurnal, Wildlife Illinois reports. They are active during the day and night, spending time hunting and then resting for awhile before resuming hunting again. They are good climbers and swimmers, and as they move about their range they often stand on their hind legs, like prairie dogs, to get a good look at everything around them. 

Both long-tailed and least weasels are mighty predators, with the least weasel earning the title of smallest carnivorous mammal in the world, according to the Indiana Department of Natural Resources. Their main food source is small mammals. Least weasels have a more specialized diet, primarily hunting mice and voles. Long-tailed weasels hunt a wider variety of small mammals, including rats, squirrels, chipmunks, shrews, moles and rabbits as well as mice and voles. Both weasels will also eat bird and bird eggs, snakes, frogs and insects. 

Weasels typically have established hunting routes that they travel over and over again, but they do not cover their entire route at once. Once they make a catch, they kill their prey by biting into its neck, according to Wildlife Illinois. When they hunt in underground burrows, they will kill any prey they encounter by biting their windpipe. 

Like some of our more familiar mammals, such as squirrels and chipmunks, weasels also cache food for later. They will hunt more than they can eat at a time and hide away extra food to eat later, Wildlife Illinois reports. 

Least weasels are generally found in open areas near water, including meadows and grasslands, Wildlife Illinois reports. The long-tailed weasel is more tolerant of humans than the seldom-seen least weasel. They too, prefer, open areas near water, but they are more likely to be seen on farms and even the edges of suburban areas. 

Neither species has a long lifespan in the wild, most often not even living a year, Wildlife Illinois reports. Least weasels breed through the entire year and can have as many as three litters of young a year when prey is easy to find. Long-tailed weasels typically breed in the summer, with babies born in spring. Litters for both species typically include an average of four to five babies, called kits or pups.

Although weasels are not often seen, we can sometimes find evidence of them through their tracks and scat. Both long-tailed and least weasels have tracks that appear in pairs, the front paws side by side and the rear paws side by side, Wildlife Illinois reports. Because of how they move, the rear paw prints are often close to or even covering the front paw prints.

As the larger of the two species, long-tailed weasels have larger paw prints, between 1 inch and 2 inches long and about an inch wide. The least weasel's prints are between a half-inch and an inch long and no more than a half-inch wide.

The scat of both is similar, about an inch long and thin and twisted. Many time you can see bones, fur and parts of insect exoskeletons in their scat, and it is most often found near their dens or on rocks and logs, according to Wildlife Illinois.