The ermine, better known as the stoat and also known as the short-tailed weasel, is a species of Mustelidae native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip. The name ermine is often, but not always, used for the animal in its pure white winter coat, or the fur thereof. In the late 19th century, stoats were introduced into New Zealand to control rabbits. The stoats have had a devastating effect on native birds. It is classed by the IUCN as Least Concern, due to its wide circumpolar distribution, and because it does not face any significant threat to its survival. It was nominated as one of the world's top 100 "worst invaders".
The stoat is an opportunistic predator, which moves rapidly and checks every available burrow or crevice for food. Because of their larger size, male stoats are less successful than females in pursuing rodents far into tunnels. Stoats regularly climb trees to gain access to birds' nests, and are common raiders of nest boxes, particularly those of large species. The stoat reputedly immobilises prey such as rabbits by mesmerising them with a "dance" (sometimes called the Weasel war dance), though this behaviour could be linked to Skrjabingylus infections.When tackling large prey, the stoat bites the nape of the neck while grasping it with its forefeet, intertwines its body around the animal then scratches its lower body with its back feet. Contrary to popular belief, blood which flows from resulting wounds is not sucked, but lapped up. The stoat may surplus kill when the opportunity arises, though excess prey is usually cached and eaten later to avoid obesity, as overweight stoats tend to be at a disadvantage when pursuing prey into their burrows. Small prey typically die instantly from a bite to the back of the neck, while larger prey, such as rabbits, typically die of shock, as the stoat's canine teeth are too short to reach the spinal column or major arteries.