Sometimes confused with mice, the typical shrew has a long, pointy snout with sensitive whiskers, a long and thin tail, tiny eyes that are sometimes hidden under their fur, noticeable ears, and fairly short legs with five clawed toes on each foot. Most have short, brown or gray fur, and many of them have red-tinged teeth. The vast majority of shrews are no bigger than a house mouse, but a few species, like the water shrews, can top 5 inches (12.5 centimeters) in head and body length. Overall, shrews range from 1.4 to 5.3 inches (3.6 to 13.5 centimeters) in head and body length and 0.06 to 1.5 ounces (2 to 40 grams) in body weight. Tails are typically from half the length to the same length as the head and body measurement. The smallest shrew, and indeed one of the tiniest living mammals, is Savi’s pygmy shrew with a body that is just 1.4 to 2.1 inches (3.6 to 5.3 centimeters) long. The tail is about half that size. The tiny shrew weighs 0.4 to 0.1 ounces (1.2 to 2.7 grams).
Common shrew can be found nearly worldwide, including North America, Central America, northern South America, Africa, Europe, and Asia.
This is a very wide-ranging family, but most species tend to prefer areas with at least some moisture. Many scuttle along the damp earth under leaf litter, but a few will climb trees in search of food. The aquatic species naturally seek out water sources that may range from bogs and swamps to streams and rivers. A few species survive well in the desert.
WHAT DOES A SHREW EAT
Shrews are not picky eaters. While insects and other invertebrates (animals without backbones) make up the bulk of their diet, they will also eat fruit and seeds, as well as small mammals, lizards, frogs, and even other shrews if food is scarce. They burn energy very quickly, so many shrews spend just about every waking moment either eating or looking for their next meal. Many species eat at least their body weight, and sometimes up to four times that amount in food every day.
BEHAVIOR AND REPRODUCTION
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 redtoothed 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.
SHREWS AND PEOPLE
Since they are small, usually active only at night, and like to hide, shrews avoid human attention most of the time. They do, however, play an important role for farmers and gardeners, who have fewer destructive insects in the crops, thanks to the shrews’ appetites. Shrews have cultural significance, as well. For example, Shakespeare’s The Taming of the Shrew is a classic tale, and people in Taiwan consider a shrew to be a symbol of good luck. On very rare occasions, shrews have bitten people. If the shrew is venomous, this can be quite painful.
According to the Red List of the World Conservation Union (IUCN), twenty-eight species are Critically Endangered, facing an extremely high risk of extinction; twenty-eight are Endangered, facing a very high risk of extinction; fifty-five are Vulnerable, facing a high risk of extinction; and four are Near Threatened, not currently threatened, but could become so.
In other words, more than one-third of all shrew species are at some risk. The U.S. Fish and Wildlife Service names one species, the Buena Vista Lake ornate shrew, as Endangered.
Many of the at-risk shrews live in limited areas and have very small known populations. This combination puts them in danger, because a single natural disaster, like a flood or one human disruption of their habitat, such as a mining operation, could destroy the entire population.