INSECTIVORE

Forest elephant shrew (Petrodromus tetradactylus). any member of the mammalian order Insectivora, which includes the shrews, moles, hedgehogs, and several lesser known groups. Of about 400 species in the order, nearly 300 are shrews of the family Soricidae. All insectivores are small, as mammals go, the largest being about the size of a small rabbit. Shrews are probably the smallest of all mammals; some species of Sorex and Crocidura weigh as little as 2.5 grams (0.09 ounce). The general body plan varies greatly within the order. Many shrews are superficially mouselike but may be distinguished from mice and other rodents by the absence of chisel-like incisor teeth. Typical moles (Talpidae) and golden moles (Chrysochloridae) are cylindrical, burrowing animals with short, thick limbs and reduced tails and eyes. Hedgehogs (Erinaceidae) and some hedgehog-like tenrecs (Tenrecidae) are stocky animals whose upper surfaces are covered with short spines. Elephant shrews (Macroscelididae; see photograph) are rather delicate animals, with long hindlegs like those of kangaroo rats or jerboas. Within the larger families the body plan is quite variable. Most insectivores live at or near ground level, except for the squirrel-like tree shrews and several aquatic moles, shrews, and tenrecs. a member of the mammalian order Insectivora, which includes the shrews, moles, hedgehogs, and other groups. Insectivores are generally small, active, nocturnal mammals that depend on insects for food. They are found in most parts of the world except Antarctica, Australia (where certain marsupials fill similar ecological niches), and South America. Forest elephant shrew (Petrodromus tetradactylus). There are nine families of living insectivores: hedgehogs and gymnures (Erinaceidae), moles (Talpidae), shrews (Soricidae), solenodons and almiquis (Solenodontidae), tenrecs (Tenrecidae), otter shrews (Potamogalidae), golden moles (Chrysochloridae), elephant shrews (Macroscelididae; see photograph), and tree shrews (Tupaiidae; classed by some authorities in the Primates). Fourteen families of extinct insectivores are known from the fossil record. Insectivores exhibit some of the characteristics of primitive placental mammals and are in general not very specialized. For those reasons it is difficult to discern when they first appeared, but tree shrews are found in the fossil record in Early Paleocene times (approximately 65 million years ago). Although insectivores are a diverse group, certain features of natural history and behaviour are common to many or most species. They are short-lived; the average life span of some shrews has been estimated at six weeks, although one year is probably a more typical figure. They tend to be solitary except during the breeding season and in the temporary association of mother and immature young, and they are frequently territorial. Most insectivores are nocturnal, but tree shrews and elephant shrews are diurnal, and some other groups, such as moles, are apparently active by day and night. Tree shrews and some tenrecs are partly arboreal, and otter shrews and some other species are partly aquatic, but in general insectivores live on the ground. The most numerous insectivores in terms of species are the shrews, which account for nearly 300 of the 400-odd species. Some shrews are very small, the tiniest of them being the Savi's pygmy shrew (Suncus etruscus) of the Mediterranean, whose body measures 35 mm (1.5 inches) in length. Shrews are extremely active, alternating periods of intense feeding with short periods of rest. The amount of food that is eaten daily may exceed double or triple their own body weight. Typically they forage in and on the leaf mold of woodlands, where they construct shallow runways. Shrews tend to be solitary but communicate with each other by various high-pitched squeaks and clicking sounds. Hedgehogs are stout, spiny animals active at dusk or at night. They take a wide range of food, including such invertebrates as millipedes, insects, and slugs, the young of ground-nesting birds, and fruits and berries. Hedgehogs are able to cope with shortages of food by becoming dormant, a state in which chemical and physiological changes help conserve energy. As a natural defense against predators a hedgehog will roll itself into a ball by contraction of a well-developed skin muscle that acts like the drawstring of a purse. Eleven species of hedgehog are known in the Old World. The related moonrats are much larger, about the size of an opossum, and lack spines. The three species live in lowland forests and mangrove swamps in Malaysia. They are recorded as being aggressive, and, when alarmed, they produce a foul smell from secretions of their anal glands. True moles form a specialized group of burrowing insectivores. The bones of the forelimbs are short and wide and are used in a backward sweeping motion when burrowing. Moles build extensive burrow systems consisting of an underground nest chamber surrounded by concentric rings of tunnels interconnected by radiating tunnels. Mounds of earth often mark their excavations. Moles feed mainly on earthworms. They detect food mainly by smell and touch. Golden moles have thick top fur and dense underfur with an unusual iridescent bronze sheen. The eyes are vestigial. These moles dig with two large pointed claws on each forefoot together with the snout, which is protected by thick leathery skin. They tend to burrow near the surface. Eleven species of golden mole are known in southern Africa. The tenrecs live only on Madagascar and the neighbouring Comoros islands. In their isolation the 20 tenrec species exhibit a variety of forms that resemble other families of insectivoreshedgehogs, shrews, water shrews, moles, etc. The common tenrec (Tenrec ecaudatus) is one of the largest insectivores, some 41 cm (16 inches) long. Its coat is a mixture of stiff hairs and spines. Most tenrecs are nocturnal and remain during the day in underground burrows. During the dry season, they burrow into the earth and become dormant. Only two species of solenodon are known from the islands of Cuba and Hispaniola. They are about the size of guinea pigs, with extremely long pointed snouts, small eyes, and large naked ears and tail. As do some other insectivores, they secrete a poisonous saliva used to subdue prey as large as mice. The population of solenodons has declined since the introduction of cats, dogs, and rats to their native islands. The three species of otter shrews are large amphibious insectivores. Two digits of the hind feet are fused and are thought to be used in grooming. Otter shrews live in tunnels in the banks of streams, and crabs appear to be a favourite item of their food. The 28 species of elephant shrews resemble long-nosed rodents. Confined to the African continent, many species live among rocky hills and scrubland, but the giant elephant shrews Petrodomus and Rhynchocycon inhabit tropical forests. Elephant shrews feed mainly on ants. Additional reading A. Cabrera, Genera mammalium, vol. 1, Insectivora, vol. 2, Galeopithecia (191925), a Spanish classica still unsurpassed illustrated review of living insectivora; Peter Crowcroft, The Life of the Shrew (1957), a review of the biology of the common Eurasian Sorex araneus; J.F. Eisenberg and E. Gould, The Behaviour of Solenodon paradoxus in Captivity with Comments on the Behavior of Other Insectivora, Zoologica, 51:4958 (1966); The Tenrecs: A Study in Mammalian Behavior and Evolution, Smithson. Contr. Zool., no. 27 (1970), a technical but easily read review of the biology of this family; F.G. Evans, The Osteology and Relationships of the Elephant Shrews (Macroscelididae), Bull. Am. Mus. Nat. Hist., 80:85125 (1942), a technical comparison of elephant shrews, tree shrews, erinaceids, and lemuroids; Gillian Godfrey and Peter Crowcroft, The Life of the Mole (Talpa europaea Linnaeus) (1960), a readable, semipopular account of the common European mole; E. Gould, N.C. Negus, and A. Novick, Evidence for Echolocation in Shrews, J. Exp. Zool., 156:1938 (1964); K. Herter, Das Verhalten der Insektivoren, Handb. Zool., vol. 8, sect. 9, pp. 150 (1957), a German language review of the behaviour of all insectivores; M.W. Lyon, Treeshrews: An Account of the Mammalian Family Tupaiidae, Proc. U.S. Natn. Mus., vol. 45 (1913); S.B. McDowell, The Greater Antillean Insectivores, Bull. Am. Mus. Nat. Hist., 115:117214 (1958), a technical review of the relationships of solenodons to other insectivores. James Smith Findley