In search of the original better mousetrap, learn about the different varieties of North American weasels habitat, history and habits.
The Weasels Habitat, History and Habits
The seemingly innocuous little creature we call the weasel
is an insatiable killer driven to murderous frenzy by a
large parasite residing in its stomach. It sucks the blood
of its victims, conceives through its mouth and gives birth
through an ear, can squeeze itself through a wedding ring,
and magically changes from brown to white within hours of
the first snowfall each winter. (See the different varieties of weasels in the image gallery).
In my research I’ve run across each of those beliefs
concerning the weasel — some several
times — recorded as myth, legend, or scientific fact.
Of course, there’s not a word of truth to any of them . . .
but lack of truth has seldom stopped people from believing
what they will about the mysteries of life. And, because of
its furtiveness, the weasel is a mystery.
That’s why such a small creature holds such great interest
for me. Even though two of the three North American weasel
species live literally just beyond my door, the secretive
little buggers continually frustrate my efforts to observe
them in the wild for more than a few seconds at a time.
Others have better luck. The trick to weasel watching, a
photographer friend tells me, is finding the rascals on
their home turf in the weasels habitat. Near their dens, he says, they’re not the
least bit shy — so long as you do nothing to startle
them. Once, my friend reports, an entire family of the
little squirts approached to within just a few yards and
cavorted for his camera.
I guess I’ve always been in the right places at the wrong
times and the wrong places the rest of the time. Or maybe
I’m just weasel jinxed. But I’ll keep at it. And between
treks to the woods, I’ll keep learning what I can from more
successful weasel watchers.
Weasels belong to the family of carnivores known to
biologists as Mustelidae — a taxonomic moniker that
translates crudely to “mouse stealers” and includes 64
species worldwide. North America’s mustelids include
weasels, badgers, skunks, otters, minks, wolverines,
fishers, martens, and the critically endangered
black-footed ferret. The smallest of the lot is the least
weasel (imagine a svelte chipmunk), the largest is the sea
otter (up to six feet tongue to tail), and the most
powerful is the wolverine.
All mustelids have highly developed anal scent glands, from
which they can emit a strong musk more or less on demand.
Unlike the skunk, most lack the apparatus to spray their
musk any distance; instead they use the noxious perfume to
mark the boundaries of their territories and for
close-range self defense.
With few exceptions, no matter where in North America you
live, you’re certain to have one or more of the continent’s
three weasel species — long-tailed, short-tailed, and
least — as a secret neighbor. While each species has
its distinctive physical and behavioral traits, the three
are more alike than different. All can take prey much
larger than themselves and strike with blurring speed. All
can climb and swim but are primarily terrestrial, making
their homes in woodpiles, under rocks or fallen logs, and
in burrows appropriated from rodents who were literally
eaten out of house and home.
Weasels are primarily nocturnal but often venture out in
daylight. All have beady, forward-set eyes with the
binocular vision necessary to successful hunters; small,
rounded, close-set ears; large brains relative to the size
of their bodies (a characteristic shared by all predators,
including humans; elongated faces and even longer necks;
slender, sleek-furred bodies; short legs; five-toed feet
with scimitar claws; and pencil-thin tails. The weasel’s
average life expectancy is about six years.
These pint-sized predators feed primarily on rodents-field
mice, ground squirrels, pocket gophers, moles, voles,
shrews, chipmunks, and rats — but also take lagomorphs
(rabbits, hares, and pikas), birds (including chickens) and
their eggs, reptiles, amphibians, insects, and fish.
In spite of their size (or lack of it), weasels are
ferocious hunters, locating their quarry primarily by scent
and shunning the common tactics of stalk and ambush in
favor of flush and chase. The weasel is both sprinter and
endurance runner, hinging its back, greyhoundlike, as it
bounds along tirelessly until it has worn down its fleeing
prey, then springing forward in a last lightning-fast leap
to seize its exhausted dinner. Additionally, the tiny
hunter’s slim and supple form enables it to weasel through
any opening large enough to accommodate its head (which
your average wedding ring isn’t), easily penetrating the
hidey-holes of its quarry — which it dispatches
instantly, with a powerful bite at the base of the skull.
Weasels need to eat an amount equal to only a quarter to a
third of their body weight daily. That means a mouse or two
a day will do. Still, when confronted with a particularly
happy hunting ground, the little terrors often will
continue killing until everything in sight is dead. Studies
indicate that movement triggers such massacres. As long as
there’s a wriggle, jiggle, or squirm in an enclosed kill
area, the weasel will press its attack, often wiping out an
entire colony of mice — numbering in the
hundreds — or a coop full of chickens in a few furious
Understandably, the weasel is considered
“bloodthirsty” — a term appearing repeatedly in most of
the biology texts I’ve read. Today we know that
bloodthirstiness is a false charge, that the weasel isn’t
some vampire guzzler of blood, and that its predatory
excesses are sparked, not by evil intent (and certainly not
by stomach parasites), but by instinct; in the weasel’s
genes it is programmed that he must lay in food when it’s
available, against those inevitable times when the pickings
will be slim. There’s little waste, since most species
cache their excess kills in underground larders for future
The once common belief that weasels, especially the
short-tail (ermine), don seasonal camouflage by changing
color from dark to white at the time of the first
significant snowfall is based, not on myth or legend, but
on relatively recent scientific research. Until the late
1800s, biologists believed that weasels shed their brownish
summer pelage and replaced it with a thicker white winter
coat in response to the lowered temperatures of autumn.
That theory was refuted when researchers noticed that
captive weasels kept in heated buildings still molted. The
researchers also noted that their mustelid prisoners began
molting within 48 hours of the first real
snowfall — and thus was born the theory that the
seasonal onset of snowfall controls the timing of the
weasel’s annual change from brown to white.
We now know that the weasel’s biannual color change stems
not from snowfall but from a decreasing photoperiod: When
days become shorter in late fall, the decreasing daylight
triggers the weasel’s pituitary gland to molt the summer
coat and simultaneously to inhibit the production of
hormones that produce the pigments coloring the weasel’s
fur. Come spring with its lengthening days, this phenomenon
reverses itself, replacing the shed white fur with a dark
The myth that the weasel conceives through its mouth and
gives birth through an ear originated in the fertile
imaginations of ancient Greek storytellers. While the truth
isn’t quite that strange, it’s highly unusual in a couple
In a process known as induced ovulation, the
female weasel releases her egg, not on a regular timetable
like most mammals, but only when it’s needed — at the
instant of copulation. There’s good reason for this: Adult
weasels are generally loners, so, rather than chancing a
mating meeting while the female’s egg is not viable, nature
invented on-demand ovulation to make certain that an egg
will be ready and waiting whenever a male might happen
along to fertilize it.
The weasel’s second unusual reproductive trait is called
delayed implantation, and applies to the
long-tailed and short-tailed species, but not to the least
weasel, which can mate and give birth at any time of year.
This biological anomaly allows mating to take place during
summer, when weasels are out and about and the most likely
to meet — but the resulting fertilized egg goes on
hold, not implanting in the uterus until late winter. This
months-long delay assures that the young will be born
during spring, when food is plentiful and living is at its
Weasel kits are born with a strong hunt ing instinct, but
must learn strategy and tactics from their mothers (with
some help from the fathers in the long-tailed species). The
kits mature rapidly and, by the winter following their
birth, are fully grown and fending for themselves.
Despite the many similarities shared by all weasels, each
of the three North American species has its own physical
and behavioral distinctions.
Least weasels(Mustela nivalis),
also known as common or pygmy weasels, have been aptly
called “cigar sized,” with adults measuring 5.2 inches to a
little over 13 inches long (of which about a quarter is
tail) and weighing as little as 25 grams (less than an
ounce). In addition to being the smallest member of the
weasel family, M. nivalis also has the distinction
of being the smallest carnivore in the world. (A member of
this tiny species could, in fact, squeeze through a wedding
ring . . . providing the ring belonged to someone with a
finger diameter of an inch or so.)
In summer, this littlest hunter’s fur is reddish brown
across the back and sides, with a white underbelly. The
least weasel keeps this two-toned coloration year-round in
the portions of its range that receive only spo radic
snowfall (though often fading to a lighter shade), but
molts to white for winter in colder climes. The most
reliable field identification feature of the least weasel
is lack of the black-tipped tail of both other species.
Short-tailed weasels ( M. erminea) are commonly known as ermines during their
allwhite winter phase, and as stoats in their darker summer
pelage. Lagomorphs are their favored foods. This species
has a reputation for playfulness, and — when not
hunting or holed up in its burrow-is known to gather in
groups to frolic in the sunshine. (Perhaps this was the
temerarious species met by my photographer friend.)
The short-tailed weasel’s summer coat is reddish brown
above, with yellowish underparts and a black-tipped tail.
In winter throughout its range-except for a strip along the
Pacific coast from British Columbia southward — the
short-tail turns pure white, save the tip of its tail,
which stays black. An adult short-tail will measure 7.5
inches to 13.4 inches nose to tip of tail, and, as you
might expect, has a shorter tail relative to its overall
length than the other two species.
Long-tailed weasels (M. frenata),
besides being the most plentiful and wide-ranging, are also
the largest of the three North American species, with
adults weighing 2.9 to 6.9 ounces and measuring 8.9 to 10.2
inches head and body, plus a generous 4 to 5.9 inches of
tail for a total length of 13 to 16 inches or so.
Northern long-tails turn white in winter (save for their
ink-tipped tails), while the various southern subspecies
merely fade to lighter shades of brown. Quite the athlete,
the long-tail may jump six feet straight up and take prey
10 times its own size. It has even attacked humans when
While humans are the only animals capable of premeditated
murder, you can’t argue that weasels don’t sometimes
indulge in instinctive overkill. Audubon reported a classic
example of just such a mustelid massacre (he watched more
than birds), writing that he had “known forty well grown
fowls to have been killed in one night by a single Ermine.”
If you suspect a weasel of raiding your hen house, search
out and plug even the tiniest coop entrances — such as
knotholes and cracks. If that doesn’t work, you’ll have to
resort to trapping the raider — live or otherwise (as
dictated by your conscience or lust for revenge, whichever
is the stronger).
Unlike the least and short-tailed species, the long-tail is
a notorious chicken killer (it’s quite possible that
Audubon’s “Ermine” was in fact a white-phase long-tail).
But even the chicken-stealing long-tail benefits the farmer
in the long run, since it destroys rats that would
otherwise prey on eggs and newborn chicks, and limits the
number of crop-damaging mice.
Just how efficient a mousetrap is the weasel? One field
study conducted in a national park netted these hungry
statistics: In 37 days of observation, a mother weasel
brought to her litter of kits a total of 148 rodents,
including 2 moles, 3 rats, 4 ground squirrels, 27 gophers,
34 chipmunks, and 78 mice. In all, a single weasel will
kill from 500 to 1,000 prey animals — mostly
mice — a year.
In the final analysis, then, that weasel hiding in the
woodpile is neither monster nor magician, but the original
(and still champion) better mousetrap.