Mammals
Stoat
Mustela erminea · also called stoat, short-tailed weasel, ermine, Beringian ermine
The stoat is a predator built like a pipe cleaner — long, thin, and quick enough to chase a vole down its own tunnel — and strong enough to kill a rabbit five times its size with one bite to the neck. Turn it loose somewhere with defenceless birds, as happened in New Zealand, and it becomes a catastrophe.
Overview
Stoats live across the Northern Hemisphere, from Arctic tundra to the northern US and the Mediterranean. They are small — males 150–450 g, females about half — with a long tubular body, short legs, and a black-tipped tail in every season. They hunt mostly voles, mice, lemmings, and rabbits, and cache surplus kills.
The killing bite
A stoat kills prey much larger than itself with a precise, powerful bite to the nape that pierces the skull or breaks the neck, wrapping its body around the struggling animal to hold on.
Ermine
In the north, the brown coat is replaced each autumn by dense white winter fur, keeping only the black tail tip. This pelt — ermine — has trimmed coronation and ceremonial robes for centuries.
Delayed birth
Females mate in summer, but the embryos pause and do not implant until spring, so young are born nearly a year after mating.
Status
The stoat is Least Concern and abundant across its native range. Introduced to New Zealand in the 1880s to control rabbits, it instead devastated native birds and is now a prime target of national predator control.
Stoat: common questions
What is the difference between a stoat and a weasel?
In Britain and much of Europe, "weasel" usually means the least weasel (Mustela nivalis) and "stoat" means Mustela erminea, and the two are easy to confuse. The reliable difference is the tail — a stoat has a distinctly longer tail with an obvious black tip, present all year, while the least weasel has a short tail that is brown to the end with no black tip. The stoat is also larger overall, has a more bounding gait, and in the north turns white in winter, whereas the least weasel usually stays brown or turns a patchy white. In North America the stoat is often called the short-tailed weasel, and the least weasel and long-tailed weasel are separate species. All are members of the same genus and hunt in the same way.
What is ermine, and why is it associated with royalty?
Ermine is the winter coat of the stoat, which in cold climates is pure white apart from the black tip of the tail. Trapped and sewn together, these small white pelts, each dotted with one black tail tip, make a distinctive white-and-black-spotted fur. From the Middle Ages, ermine was reserved by sumptuary laws for royalty and high nobility in Europe and used to trim and line coronation robes, judges' and academics' hoods, and peers' ceremonial dress, with rank often indicated by the number of black "tails" shown. The look is still imitated in the ceremonial robes of the British monarchy and House of Lords, and "ermine" appears as a fur pattern in heraldry. Producing it historically required killing very large numbers of stoats.
How can a stoat kill an animal so much bigger than itself?
By specialising in a fast, precise, lethal bite rather than overpowering prey with bulk. A hunting stoat is relentless and agile, following rabbits and rodents into their burrows and runs, and when it catches up it grips the prey with its forelimbs and delivers a hard bite to the back of the skull or the top of the neck, killing quickly by penetrating the braincase or breaking the neck. Its long, thin, muscular body lets it wrap around struggling prey and hang on. Stoats also sometimes perform a strange, leaping, twisting "dance" near rabbits, which may confuse or transfix the prey, or may simply be a response to a parasitic worm; the effect and the cause are both debated.
Why are stoats such a problem in New Zealand?
New Zealand evolved with no land mammals except bats, so its birds, many of them flightless or ground-nesting, developed no defences against mammalian hunters. Stoats were deliberately introduced from Britain in the 1880s, along with ferrets and weasels, in a misguided attempt to control the rabbits that earlier settlers had released. The stoats spread rapidly, and instead of solving the rabbit problem they became one of the country's worst predators of native wildlife, killing kiwi chicks, mohua, kaka, kakariki, whio, and many other birds, as well as lizards and giant invertebrates. Today stoats are a central focus of New Zealand's Predator Free 2050 programme, targeted with trap networks, and in some places aerial baiting, especially during "beech mast" years when rodent and then stoat numbers explode.