Shrew

The shrew (family Soricidae) is a small mole-like mammal classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, or the West Indies shrews, which belong to different families or orders. Although its external appearance is generally that of a long-nosed mouse, a shrew is not a rodent, as mice are. It is, in fact, a much closer relative of hedgehogs and moles, and shrews are related to rodents only to the extent that both belong to the Boreoeutheria magnorder – together with humans, monkeys, cats, dogs, horses, rhinos, cattle, pigs, whales, bats, and others. Shrews have sharp, spike-like teeth, not the familiar gnawing front incisor teeth of rodents. Shrews are distributed almost worldwide; of the major tropical and temperate land masses, only New Guinea, Australia, and New Zealand have no native shrews; in South America shrews appeared only relatively recently, as a result of the Great American Interchange, and are present only in the northern Andes. In terms of species diversity, the shrew family is the fourth-most successful mammal family, being exceeded only by the muroid rodent families Muridae and Cricetidae and the bat family Vespertilionidae. All shrews are comparatively small, most no larger than a mouse. The largest species is the Asian house shrew (Suncus murinus) of tropical Asia, which is about 15 cm long and weighs around 100 g; several are very small, notably the Etruscan shrew (Suncus etruscus), which at about 3.5 cm (1.4 in) and 1.8 g (0.063 oz) is the smallest living terrestrial mammal. In general, shrews are terrestrial creatures that forage for seeds, insects, nuts, worms, and a variety of other foods in leaf litter and dense vegetation, but some specialise in climbing trees, living underground, living under snow, or even hunting in water. They have small eyes and generally poor vision, but have excellent senses of hearing and smell. They are very active animals, with voracious appetites. Shrews have unusually high metabolic rates, above that expected in comparable small mammals. Shrews in captivity can eat 1/2 to 2 times their own body weight in food daily. They do not hibernate, but are capable of entering torpor. In winter, many species undergo morphological changes that drastically reduce their body weight. Shrews can lose between 30% and 50% of their body weight, shrinking the size of bones, skull, and internal organs. Whereas rodents have gnawing incisors that grow throughout life, the teeth of shrews wear down throughout life, a problem made more extreme because they lose their milk teeth before birth, so have only one set of teeth throughout their lifetimes. Apart from the first pair of incisors, which are long and sharp, and the chewing molars at the back of the mouth, the teeth of shrews are small and peg-like, and may be reduced in number. The dental formula of shrews is:3.1.1-3.31-2.0-1.1.3 Shrews are fiercely territorial, driving off rivals, and coming together only to mate. Many species dig burrows for catching food and hiding from predators, although this is not universal.