Insectivora is the third largest order of mammals after the rodents and bats. Most of the insectivores are smaller than a child's hand, and shrews are some of the smallest mammals known. A few, however, reach a foot long (30 centimeters) or more. The largest insectivore is the moonrat, which stretches 24 inches (60 centimeters) long from the tip of its snout to the end of its tail.
A typical insectivore is covered with smooth fur, although some, like the hedgehogs, have spines. They usually have five clawed fingers or toes at the end of each of its four, short legs, but the tenrecs and golden moles have only four claws. Their skulls are small, long, and flat, however the furry coat may make the head appear larger. They also have tiny, often unnoticeable ears and eyes. Insectivores have an excellent sense of smell that is assisted by their snouts, which may be long and flexible, or short and stout. Many insectivores have rows of stiff sensory hairs, called vibrissae (vuh-BRIS-ee), on their snouts, tails, ears, and sometimes feet. Beyond this general description, these animals vary widely.
Insectivores occur worldwide except Antarctica, Australia, and northern South America.
Insectivores live primarily on land, typically at ground level or beneath it. A few species, like the Asiatic water shrews, are aquatic. Insectivores can survive in a wide range of habitats from tropical rainforests to temperate marshes, from thick forests to open fields, and from sea-level deserts to mountainsides up to 14,760 feet (4,500 meters). Some fossorial, underground, species, like the star-nosed mole, prefer to burrow in the wet soil around freshwater marshes and occasionally venture into somewhat salty, brackish, waters, while others, like the eastern mole, use enlarged, shovel-like forefeet to tunnel through the drier soils of forests and fields. The gymnures prefer hiding places among tree roots or fallen branches, sometimes even inside termite mounds. Shrews, which comprise almost three-quarters of all species in the order, spend much of their time in shallow depressions that they dig beneath some form of shelter, including rocks, logs, and fallen leaves.
As the name of the order implies, most of these animals primarily eat insects, although many will also eat other invertebrates, animals without a backbone. In addition to insects, many will also eat leaves, tender shoots, seeds, fruits, and other plant materials. Some, like hedgehogs and tenrecs, prefer to dine on invertebrates other than insects, such as snails, clams, and worms, or on vertebrate animals, animals with a backbone, like small snakes or lizards, fish, frogs, and bird eggs.
Many insectivores require a lot of energy, so they must eat frequently. Some, like the long-tailed shrew, spend almost every waking moment eating in order to meet their energy needs.
BEHAVIOR AND REPRODUCTION
These active little mammals prefer to remain out of sight, whether that is underground in tunnels, beneath leaf litter or brush piles, under rocks, or in some species, in the water. Typically nocturnal, active at night, although a few are active during the day. Insectivores have poor eyesight and they must rely on other senses. Sensory hairs, which are located on various parts of their bodies, heighten their sense of touch and make them extremely sensitive to their surroundings. Their hearing is also good, and the animals communicate with others of their own species and with other animals through a variety of squeaks, hisses, whistles, and buzzes. Insectivores have a keen sense of smell, which is important in locating and identifying prey, picking up the scent markings that border the territories of other insectivores, and in finding mates during the reproductive season. The moles and desmans have sensory receptors called Elmer's organs on their snouts, to identify and possibly to locate food items.
Insectivores' best defense against predators, animals that hunt them for food, is to remain hidden, so that predators are more likely to overlook them. Some, however, use other defense tactics. Hedgehogs, for example, can erect their spines to present an intimidating barrier to attacker. Some shrews and solenodons actually produce venom that they transfer with their bites in order to capture prey. Many species, especially shrews, will also attack members of their own species—not for food, but to protect territory. When placed in a confined space, shrews will typically charge one another, sometimes locking together and inflicting tearing bites until one dies.
Insectivores are typically active all year long, even in climates where temperatures in the winter drop below freezing. In colder areas of North America, for example, shrews are sometimes seen scurrying across the snow. A few, like some hedgehogs and tenrecs, hibernate, a dormant state where the animal does not eat or pass wastes, or go into a hibernation-like state when temperatures dip too low or when food becomes scarce.
For many insectivores, details about their reproductive behavior and their early development are unavailable. In general, however, individual insectivores remain alone all year, except during the breeding season. Even then, males and females come together for a very short time, and the male leaves the female well before she has her offspring. Depending on the species, an insectivore may mate once a year with many offspring, as the tenrecs do, or several times a year with fewer offspring per litter, which is common in many moles. Often the young of several nearby females will have the same father. The young of all species are born fully developed, with some becoming independent of their mothers within a few weeks, while others rely on their mother for food and protection for several months. In an unusual display of mother-and-child interplay, the mother in a few shrew species will lead the family in a caravan, with one youngster gripping the tip of her tail with its teeth. A second youngster does the same to the first youngster and on down the line, until the entire three to seven member family is all linked together in a row.
Most insectivores live only about a year, but a few, like the solenodons, may live several years in the wild.
INSECTIVORES AND PEOPLE
For the most part, people rarely see insectivores and are not affected by them. A few, like the eastern mole, make above-ground mounds when they tunnel, which are visible and may present a source of frustration to people who want to maintain a perfect lawn. The majority of insectivores are small and inactive during the day, which makes them poor pets. Hedgehogs, however, are larger, easy to keep, and have become quite popular in homes around the world.
Dozens of insectivores around the world are threatened, according to the World Conservation Union (IUCN). Thirty-six are listed as Critically Endangered, facing an extremely high risk of extinction in the wild. Forty-five are Endangered, facing a very high risk of extinction in the wild, and eighty-eight are Vulnerable, facing a high risk of extinction in the wild. In the United States, only the Buena Vista Lake ornate shrew is listed as Endangered by the U.S. Fish and Wildlife Service.
ARE THEY ALL INSECTIVORES?
Scientists are beginning to rethink exactly which animals should be placed in the order Insectivora. Many scientists believe that two of the families traditionally placed under the Insectivora should fall under a separate order known as Afrotheria. Under this arrangement, the tenrecs and golden moles would be classified in Afrotheria with such animals as elephants and aardvarks. While this controversy continues, field biologists are still finding new species, especially in the tropics of Africa where the small, hidden shrews are particularly difficult to find.
Habitat destruction has proven to be the biggest danger to these species. As humans clear forests, farm more land, and use toxic chemicals to control plants and animals, populations of these small animals can be destroyed.
FOR MORE INFORMATION
Nowak, R. Walker's Mammals of the World, 6th ed. Baltimore: Johns Hopkins University Press, 1999.
Wilson, D., and S. Ruff, eds. The Smithsonian Book of North American Mammals. Washington, DC: Smithsonian Institution Press, 1999.
"2003 IUCN Red List of Threatened Species." World Conservation Union. http://www.redlist.org (accessed on July 1, 2004).
Haberl, Werner. The Shrew-ists Site.http://members.vienna.at/shrew/index.html (accessed on July 1, 2004).
"Threatened and Endangered Species System (TESS)." U.S. Listed Vertebrate Animal Species Report. http://ecos.fws.gov/tess_public/TESSWebpageVipListed?code=V&listings=0#A (accessed on July 1, 2004).
University of Michigan Museum of Zoology. "Order Insectivora." Animal Diversity Web.http://animaldiversity.ummz.umich.edu/site/accounts/information/Insectivora.html (accessed on July 1, 2004).
Insectivore Specialist Group (ISG). Hamburgerstrasse 11, A-1050 Vienna, Austria. E-mail: [email protected] Web site: http://members.vienna.at/shrew/itses.html.
IUCN/SSC Afrotheria Specialist Group. Web site: http://www.calacademy.org/research/bmammals/afrotheria/ASG.html.
European Hedgehog Research Group (EHRG). Phone: +47 370 36 509. Fax: +47 370 35 050. E-mail: [email protected] Web site: http://www.ngo.grida.no/ngo/hedgehog/.