Shrews are distributed almost worldwide: of the major temperate land masses, only New Guinea, Australia, and New Zealand do not have native shrews at all; South America has shrews only in the far-northern tropics, including Colombia. In terms of species diversity, the shrew family is the fourth most successful of the mammal families, being rivalled only by the muroid families Muridae and Cricetidae and the bat family Vespertilionidae.
All shrews are small, most no more than mouse size. The largest species is the House Shrew (Suncus murinus) of tropical Asia which is about 15 cm long and weighs around 100 grams; several are very small, notably the Etruscan Shrew (Suncus etruscus) which at about 3.5 cm and 2 grams 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, in the subniveal layer 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 and unusually high metabolic rates. Shrews must eat 80-90 % of their own body weight in food daily. They are not able to hibernate.
Whereas rodents have gnawing incisors that grow throughout life, the teeth of shrews wear down throughout life, a problem made more extreme by the fact that they lose their milk teeth before birth, and therefore have only one set of teeth throughout their lifetime. 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:
Shrews are fiercely territorial, driving off rivals, and only coming together to mate. Many species dig burrows for caching food and hiding from predators, although this is not universal..
Female shrews can have up to ten litters a year, and the animals only stop breeding in the winter in temperate zones, and breed all year round in the tropics. Shrews have a gestation period 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 live for between 12 and 30 months.
Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species of shrew are venomous. Also, along with the bats and toothed whales, some species of shrew use echolocation. Unlike most other mammals, shrews lack a zygomatic bone (also called the jugal), and therefore have an incomplete zygomatic arch.
Shrews hold nearly 10% of their mass in their brain, a relatively high brain to body mass ratio.
The only terrestrial mammals known to echolocate are two genera (Sorex and Blarina) of shrews and the tenrecs of Madagascar. These include the Vagrant Shrew (Sorex vagrans), the Common or Eurasian Shrew (Sorex araneus), and the Northern Short-tailed Shrew (Blarina brevicauda). The shrews emit series of ultrasonic squeaks. In contrast to bats, shrews probably use echolocation to investigate their habitat rather than to pinpoint food.
In the English language, the word shrew is also used to describe a woman with a violent, scolding, or nagging temperament, as in Shakespeare's play The Taming of the Shrew. The animals were believed historically to behave aggressively and with cruelty, and to have a poisonous bite; the term "shrew" was then applied to a person thought to have a similar disposition.
Shrew was one of the names originally proposed for the British Fighter Airplane which finally became known as the Spitfire and played a key role in the Second World War.