Least Weasel

Yes, if carnivore is taken to mean a member of the mammalian order Carnivora, the meat-eating mammals. Small females of the least weasel are the tiniest members of that whole order, lighter than many mice, and even a large male is smaller than a typical rat. It is worth noting that other very small mammals, such as the Etruscan shrew, are lighter still, but shrews are not carnivorans, they belong to a different order, so the least weasel keeps the title within the group that includes cats, dogs, bears, and seals. Its small size is not a quirk but the whole point of its way of life, letting it hunt prey that lives in spaces no other carnivoran can enter.

Because its shape works against it in the cold. A long, thin body has a large surface area relative to its volume, so it loses heat quickly, and there is no room in a tube-shaped animal to carry a useful fat reserve. To keep its body temperature up, a least weasel has to burn energy at a high rate, which means eating a large amount relative to its size, roughly a quarter to a third of its body weight in prey every day. If it fails to catch enough for even a day or two, it can die of starvation and cold. This is why weasels hunt almost constantly, are active in short bursts around the clock, and cache extra kills whenever they can.

They are close relatives and look similar, both long, thin, short-legged predators with brown backs and pale bellies, but there are reliable differences. The stoat is larger, with a longer tail that has a distinct black tip in all seasons, while the least weasel is smaller and its shorter tail is all brown. The border between the brown upper parts and the white under parts is a straight, slightly wavy line on the weasel and a sharp, clean line on the stoat. In winter in the north, a stoat that has turned white keeps its black tail tip and is then called an ermine, whereas a white weasel is white all over. The old memory aid is that a weasel is weaselly distinguished by being smaller, and a stoat is stoatally different by the black tail tip.

Not to people. A least weasel is far too small to be a threat, and it will flee from a human, though a cornered one will hiss, chatter, and bite in self-defence, and the bite from those needle teeth is sharp. Around a farm or a garden the weasel is generally an ally, because its diet is dominated by the mice and voles that damage crops, stored grain, and gardens. The one situation where a weasel can be a nuisance is a poultry run or a nest box, since a weasel can enter through a very small gap and will take eggs, chicks, and sometimes adult birds, so runs and boxes in weasel country need to be built tight.