Shrews: Soricidae

Most shrews are active at night and rest during the day. A few, however, like the long-tailed shrew, stay awake for much of the day trying to feed their hefty appetites. When they can't find enough food, some species may spend a few hours in an inactive state called torpor that decreases their energy needs. Unlike most other mammals, some shrews actually produce venom to immobilize their prey, and then either kill the prey immediately or save it for a later meal. European water shrews, for instance, have a deep groove in the lower front tooth to help direct the venom from a duct at the base of the tooth into the prey.

Shrews are well-known for being aggressive toward members of their own species and sometimes other species. By making and marking small territories with scents, they typically avoid one another and thus sidestep fights. However, when two shrews, like the short-tailed shrews of North America, encounter one another in a confined space, they will commonly attack quickly and continuously, often until one dies. Despite their reputation as fighters, a few species tolerate other shrews quite well. Adult small-eared shrews will even share a nest.

Most shrews spend their whole lives on land, usually running from place to place. A few species are good swimmers. These aquatic shrews typically have stiff, fringed hairs on their feet that serve to enlarge the surface area of their feet and help them paddle through the water. The elegant water shrew has actual webbing on its feet to aid in swimming.

Shrews generally breed two or more times a year, giving off specific odors or making characteristic movements, such as tail-wagging in house musk shrews, to announce that they are ready to give up fighting long enough to mate. Females may mate with several males during each breeding period, so the offspring in one female's litter may have several different fathers. Many species build nests. The short-tailed shrew, for example, makes a small nest of leaves and grass in a hidden spot, often under a rock or inside a tunnel. Pregnancies last only three to four weeks for most species, and the babies are small and quite helpless. The number of offspring varies, but three to seven is a common litter (young born at the same time) size for shrews. Babies grow very rapidly and are ready to face the world on their own at just three to four weeks old. Before they do so, however, some species of the group, known as white-toothed shrews because they lack the reddish tinge seen in other shrews, take part in an odd behavior. The mother leads them around in a row, with each shrew using its teeth to grasp the hair on the rump of the one in front of it. This line-up of shrews is called a caravan, or chain behavior. Scientists now believe that families of some red-toothed shrews may use this peculiar but effective method of travel, as well.

As noted, shrews develop quickly and they begin having young of their own before they reach their first birthday. Shrews rarely live much past fourteen to eighteen months of age.