Enemies
The great-horned owl, barn owl and long-tailed weasel are to be counted as enemies since Nelson (1934:252) found the fur, skull and other fragments of the skeleton of a least weasel in one of 26 pellets of the great-horned owl in Wisconsin; Handley (1949:431) found the skull and other skeletal remains of a least weasel in one of 22 pellets of the barn owl in Virginia; and Polderboer, Kuhn and Hendrickson (1941), in Iowa, found the remains of a least weasel in the den and scats of a Mustela frenata. A domestic cat in Michigan killed a least weasel (Dearborn, 1932B:277).
Food
Mice are killed by the least weasel biting into the back of the head and neck according to Allen (1940:460) who reported upon the growth of five young, from Michigan, that he had in captivity. He further states that a weasel was able to kill a mouse in 30 seconds. One large Microtus introduced into the cage slept with a weasel for several days and ate parts of the mice that the weasel killed but then the weasel killed this mouse! Llewellyn (1942:440-441), in writing of a captive from Virginia, says: "When a live mouse was placed in the cage, the weasel sprang upon it almost instantly. Grasping the mouse by the back of the head, the weasel bit its victim through the skull several times in rapid succession and held on with its sharp teeth. The sound of the teeth piercing the bone was distinctly audible at a distance of several feet. During this interval the weasel hugged the mouse closely with its fore legs and pressed it firmly to its belly through a kicking motion of the hind legs. The hold on the back of the head was not relinquished until the mouse was dead. The killing took only a few seconds. Upon releasing the mouse the weasel usually came to the front of the cage and inspected the observer for an interval of several seconds after which it returned to its prey and began its meal at once. Sometimes the blood would be licked from the wound in the back of the head or perhaps an ear would be chewed a bit and the blood licked off, but never did the weasel 'cut the throat' of its prey and 'suck the blood.'
"The weasel ate the head and brain first, beginning at the back of the head and working forward. Just before reaching the nose the process was reversed and eating then proceeded from the base of the skull toward the tail of the mouse. The tip of the nose, maxilla with teeth, and the tail seemed to be the parts least preferred; they were not eaten when an abundance of food was present. At no time did the weasel place its front feet on the mouse in an attempt to hold it. A second or third mouse was killed immediately upon being placed in the cage even though the first one had not been consumed. The weasel, however, usually returned to the partially eaten mouse and finished it before starting on a new one. Upon completing a meal, especially if the meal had been particularly bloody, the weasel rubbed its chin on the bottom of the cage, scooting along and appearing more snakelike than normal. Whenever I attempted to remove a mouse, or partially eaten one, from the cage, the weasel hung to the mouse tenaciously, and often allowed itself to be lifted up in this manner.
"In the six days that the weasel was kept in captivity it was fed 10 house mice having a total weight of 118 grams. As no food was given on one day, the amount of food eaten is probably slightly below the actual capacity of the animal. Since the weasel weighed only about 32 grams, the average amount of food eaten a day was slightly in excess of one-half the weight of the animal."
Polderboer (1942:146-147) found in three dens, in Iowa, bits of Reithrodontomys (harvest mice) and Peromyscus maniculatus (deer mouse), and in the digestive tract of one least weasel there was a bone fragment and a few hairs of a deer mouse. In the account, given beyond, of a nest, Criddle (1947:69) records the Pennsylvania meadow mouse (Microtus pennsylvanicus drummondi) and the Gapper red-backed vole (Clethrionomys gapperi) as prey at Treesbank, Manitoba. The same author, concerning the same place, earlier (1926:199-200) wrote that in 1922 the meadow mouse, Microtus minor, "went into winter quarters in great numbers and its homes were well stocked with provisions . . . all went well until the middle of February, 1923. Then, within a few days, each was taken possession of by a least weasel (Mustela rixosa) and the inhabitants were quickly destroyed. One dwelling was occupied by one of these weasels for about two weeks during which time I observed that it had dragged several mice over the snow to its temporary home. This residence was examined in April, and in it were discovered six dead Microtus minor, one Evotomys, the head of another, and at least six or eight remnants of small rodents including Microtus drummondi, these last remains being chiefly indicated by the hair-lined nest of the weasel.