The weasel family has a reputation for being ferocious hunters, and long-tailed weasels (Mustela frenata) are no exception. This ferocity has resulted in a negative perception of weasels as indiscriminate bloodthirsty killers, but long-tailed weasels are simply efficient predators and their reputation for being bloodthirsty may come from the fact that they often kill prey as large as or larger than themselves and so must attack swiftly and effectively. This speed and determination can often look vicious.
This hunting strategy has helped the long-tailed weasel become the most widespread mustelid species in the western hemisphere (click here for range map). Weasels are very active hunters, and prefer to hunt in small tight spaces rather than the open. Long-tailed weasels are one of the most generalist weasels, and kill all types of rodents and rabbits up to the size of snowshoe hare, but they rarely eat plants and fruit.
Their long thin bodies and small head allow them to squeeze into all kinds of burrows and holes in search of prey. Above ground hunting is characterized by moving in a zig-zag fashion through the landscape while investigating all available nooks and crannies for prey. Weasels also burrow in the snow, hunt in rabbit runs and pocket gopher burrows, and under logs and other tight spaces. If a long-tailed weasel encounters prey underground or in tight quarters they will typically grab the prey by the throat and suffocate it. In more open ground a weasel will tackle and wrap rodents up with its long sinuous body, usually killing them with a bite at the base of the neck that severs the spine. Rabbits and larger prey are chased and repeatedly struck and bitten which eventually wears the prey down to the point that the weasel can jump on the back of the prey and deliver the killing bite to the base of the neck.
Weasels gained their blood thirsty reputation because often the first thing a weasel will do after killing is to lap up the blood from bite wounds, gaining valuable liquid and sustenance. The head and brains are the next thing to be eaten, and then the organs, and finally the muscle. Every bit of food counts for long-tailed weasels, and due to their high metabolism and active hunting style they must eat 30% of their body weight a day to survive. Weasels also stay active year round and must kill even more to survive in the winter.
For more information about weasels see:
Elbroch, Mark and Kurt Rinehart. Behavior of North American Mammals. New York: Houghton Mifflin, 2011. 374 pgs.
Sheffield, S. R. and H. H. Thomas. 1997. Mustela frenata. Mammalian Species 570:1-9.