Least among us: Weasel common, but seldom seen

For a variety of reasons, I got behind in mowing trails in the hayfield this summer. My wife insists I keep them well groomed because she’s afraid she’ll encounter one of those long slithering creatures. So when I finally got to it on Saturday, the grass was about 8 inches tall.

Experience has taught me to go slowly when I mow, especially when the grass is high. Doing so has saved many box turtles, meadow voles, and even a few of those slithering creatures over the years. That’s how I happened to notice a dark form lying in the grass before me.

Rarely seen

I stopped the mower to investigate and found a small mammal I’ve seldom seen in nature. It was North America’s smallest carnivore, a least weasel — chocolate brown above and white below, and about 7 inches long, including its 1-inch tail.

Back at the house, it weighed in at just under 2 ounces. Other than being dead, it was in perfect condition.

Though commonly prey to owls, hawks, snakes, foxes and larger weasels, this one seemed to have died a natural death. It was limp and still warm. Perhaps it starved to death.

Least weasels are metabolic dynamos and require about half their body weight in food every day. Maybe it was an older individual and could no longer meet the demands of daily life.

Healthy least weasels are a bit smaller than chipmunks, and though seldom seen, they are probably common in old fields, meadows, and marshes. They eat voles, mice, insects, small birds, and eggs.

Efficient hunter

These highly efficient killers grab their prey by the head and subdue it by wrapping their legs around the victim’s body. After a few quick bites to the base of the skull, death is almost instantaneous.

In fact, if small mammals experience fear, their greatest terror may come from least weasels. Thanks to a long tubular body, they can explore almost any burrow they find. So while a mouse or a chipmunk can escape hawks and owls by dashing underground, there is no safe haven from least weasels. At any moment these tiny predators might appear in the sleeping quarters of underground prey. It almost doesn’t seem fair.

Larger species. Two larger species of weasels inhabit woods and fields, so prey as large as cottontails, squirrels, and young ground hogs are subject to weasel attacks. Long-tailed weasels are the largest and most widely distributed of the three common North American species. They measure up to 17 inches long, including tail.

Ermine, or short-tailed weasels, grow to about 11 inches in length.

During the spring and summer, weasels are brown above and white below. But in the fall, weasels molt into an almost pure white pelage that creates a perfect camouflage when the snow flies.

In the southern part of their range, long-tail weasels retain their brown fur all year long.

On the go

Though most active between dusk and dawn, weasels hunt any time they’re hungry. Their small size and secretive nature, however, make them difficult to observe.

They spend much of their time exploring the grassy runways of meadow voles and underground burrows of other small mammals. During winter, they often tunnel beneath the snow.

Making more weasels

Unlike many small mammals, which breed in the spring, weasels have adopted a different reproductive strategy. Least weasels can breed at any time of year, even in mid-winter. When prey is abundant, they take advantage of the situation and make more weasels. Two to three litters per year are typical.

Gestation lasts about 36 days, and litter size averages five.

Ermine and long-tailed weasels bear a single litter of five to eight young each year. These two species mate in mid-summer, but the tiny embryos do not implant on the female’s uterine wall until sometime in the spring.

This “delayed implantation” allows males and females to complete the energetically demanding task of mating when food is abundant rather than waiting until spring when food is often in short supply.

Another adaptation among weasels reduces competition for food between the sexes. In all three species, males are as much as 25 percent larger than females. This sexual size dimorphism enables a pair of weasels to eat different sized prey.