The shrew is a small mole-like mammal in the family Soricidae.
There are about 385 species of shrews.
Shrews are found throughout North America to northwestern South America, Africa and Eurasia; of the major tropical and temperate land masses, only New Guinea, Australia, and New Zealand have no native shrews.
They have adapted to a wide variety of environments, inhabiting tundra, coniferous, deciduous, and tropical forests, savannas, humid and arid grasslands, and deserts.
The lifespan of shrews is from 12 to 30 months, depending on the species.
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) [Photo below], which at about 3.5 cm (1.4 in) and 1.8 g (0.063 oz) is the smallest living terrestrial mammal.
Shrews appearance: they have cylindrical bodies, short and slender limbs, and clawed digits. Their eyes are small but are usually visible in the fur, the ears are rounded and moderately large and a long, pointed snout is movable. Tail length varies among species, some being much shorter than the body and others appreciably longer.
Whereas rodents have gnawing incisors that grow throughout life, the teeth of shrews wear down throughout life; tooth wear can therefore become a problem, and older adults may starve to death when their teeth become too worn to function.
They have generally poor vision, but have excellent senses of hearing and smell.
Shrews are active throughout the day and night.
They have high metabolic rates and may consume more than their own weight in food daily; Shrews cannot survive for more than a few hours without eating. As a result, their life consists largely of a frenetic search for food.
They eat primarily insects and other invertebrates but also take small vertebrates, seeds, and fungi. A few kinds of shrews are aquatic, well adapted to swimming and catching aquatic invertebrates and small fish.
Shrews provide a valuable service for humans beings, as they consume pest insects and slugs that can damage crops. Beyond this, their small size, savage reputation, and unique behaviors have captured the interest and imaginations of people, adding to the wonder and mystery of nature.
Many species dig burrows for catching food and hiding from predators, although this is not universal.
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.
Shrews emit clicks, twitters, chirps, squeaks, churls, whistles, barks, and ultrasonic sounds in contexts of alarm, defense, aggression, courtship, interactions between mother and young, and exploration and foraging.
Female shrews can have up to 10 litters a year; in the tropics, they breed all year round; in temperate zones, they cease breeding only in the winter. Shrews have gestation periods of 17–32 days. The female often becomes pregnant within a day or so of giving birth, and lactates during her pregnancy, weaning one litter as the next is born.
Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species of shrew are venomous. Also, the only terrestrial mammals known to echolocate are some species of shrews.