Insect-eating mammals

Insectivora is probably the most ancient living order of eutherian mammals. These insect-eating mammals are known to have lived as much as 100 million years ago, sharing their world with the dinosaurs. All insectivores share certain basic features, but each species is specialized for a different way of life. Along with such non-insectivore orders as bats (Chiroptera), which are generally considered to be descended from Insectivora; anteaters, sloths and armadillos (Edentata); pangolins (Pholi-dota); and some primates, insectivores form the majority of a large group of mainly insecteating mammals. Although many species belonging to other orders, including rodents and foxes, also feed primarily on insects, this section discusses only those species whose entire family and order have evolved to consume insects and other invertebrates.

The diversity of insectivores is reflected in their limb structures. AH have basically pentadactyl (five-toed) limbs, modified to suit their life styles. Shrews walk on their toes, whereas a mole’s digits form a broad spade for digging. Anteaters have an enlarged third digit with a curved claw for breaking open ant and termite nests. Bats have four elongated digits on the forelimbs, which support the membranous wing.

Insectivore classification

Today, Insectivora is the third largest order of mammals, occurring throughout the world and comprising four suborders and about 410 species. Most insectivores belong to the suborder Lipotyphla, which includes moles, solenodons, tenrecs, desmans, golden moles, hedgehogs, moonrats, and shrews. Other suborders include Zalambdodontia, or the water shrews (also known as otter shrews); Macroscelidea, or the elephant shrews; and Dermoptera, which contains the flying lemur, the most accomplished of gliding mammals.

Typically, insectivores are small, nocturnal mammals with elongated, narrow snouts. Most are distinguished from other small mammals by the fact that they have five digits on each limb—most rodents, for example, have four or fewer. Each digit has a distinct claw. The body is covered with short, dense fur. In some species, such as hedgehogs and tenrecs, some of the hairs are developed into spines. Insectivores often have small ears and small eyes with poor vision. Their senses of smell and hearing, however, are usually sharp. The brain has a primitive structure, ana the placenta is simpler than that of most other mammals. Insectivores have up to 44 teeth— the largest number normally found in placental mammals. These usually have sharp cusps that enable them to slice their prey.

Insectivores include ground-living, burrowing, climbing, and even semiaquatic species. They feed on insects, grubs, snails, and occasionally on helpless vertebrates, such as the young of ground-nesting birds. Many insectivores are extremely active and need to be refueled constantly by large quantities of food.

Most bats (far left) eat insects and hunt their prey at night using echolocation (left). While flying through the air at up to 15 miles (24 kilometers) per hour, they generate high frequency sounds and detect prey or obstacles by the echoes they reflect. The range of detection is, however, limited to 3 feet (1 meter) or so, but is sufficiently discriminating to enable some bats to catch fish by detecting the ripples they make on the water surface.

Habitats and life styles

The solenodon is about the size of a rat and has a pointed snout. It uses this sensitive snout to root about on the ground for invertebrates and plant material. It also eats lizards, frogs, and small birds. Like some other insectivores, it produces a toxic saliva from a gland in the lower jaw. Of the two species of solenodon, one, last seen in Cuba in 1909, is now thought to be extinct The other lives on the island of Hispaniola in the West Indies.

The tenrec family (Tenrecidae) includes about 20 species, all of which are found on Madagascar and the Comoros islands. They retain some reptilian features, such as a cloaca. Tenrecs have adapted to fill a wide range of habitats in Madagascar. Some resemble shrews. Those of the genus Setiferov Echinops have sharp spines and resemble hedgehogs. Others are similar to mice and moles. Their main diet consists of small invertebrates and plant material.

The family Talpidae consists of about 29 species of mole, shrew-mole, and desman, which occur widely in the Northern Hemisphere. Most are borrowers and are highly modified for an underground existence, with powerful spadelike front feet, tiny weak eyes, and no external ears. The short, fine hairs on the body can be brushed in any direction, enabling them to reverse easily in their tunnels. The desmans, which are the largest of this group, lead a semiaquatic life in or near ponds and streams, feeding on aquatic invertebrates and fish. They use their long noses as snorkels, turning them up so that they stick out of the water.

Golden moles, which resemble true moles, form the family Chrysochloridae and are found in a range of habitats in Africa. They have a blunt snout covered with a leathery pad. The eyes are tiny and weak, and the front feet are armored with powerful claws for efficient burrowing. Golden moles are diurnal—that is, they are active during the day—and feed on a range of underground invertebrates. Some desert-dwelling, sand-burrowing types, such as the desert golden mole, even capture and kill burrowing reptiles.

The hedgehog family (Erinaceidae includes the familiar hedgehogs, with their covering of sharp, tough spines, and the more rodentlike, long-snouted moon rats. There are 17 species in all, found in Europe, Asia, and Africa. Erina-ceids are nocturnal. They feed on invertebrates, carrion, and small mammals.

The shrews of the family Soricidae are the most successful insectivore group in terms of numbers. There are about 250 species, and they inhabit almost every corner of the world. Most shrews are small. The smallest, the pygmy shrew, weighs less than 0.09 ounce ‘2.5 grams). Shrews forage on the ground, moving under logs, plant debris, and into crevices in search of invertebrate prey. Some are able to subdue larger animals such as mice and frogs because, like solenodons, they also have a highly toxic substance in their saliva. The prey is rendered helpless by just a few bites from these venomous animals. Shrews communicate by high-pitched squeaks and high-frequency noises that humans cannot hear.

The water shrews of the order Zalamb-dodontia are distinguished from other insecti-vores by their five-cusped molars, with the cusps arranged in a W-shape. This formation is almost identical to that of the earliest eutherian mammals. Water shrews lead a semiaquatic life in streams, rivers, and swamps, feeding on fish, crabs, and frogs. The giant otter shrew is the largest living insectivore, with a length of about 24 inches (60 centimeters). With its sleek, dense coat and powerful tail, it resembles a small otter.
The elephant shrews differ from other insec-tivores in that their hind limbs are adapted for hopping. There are about 18 species of elephant shrews, and they are found in Africa in habitats ranging from semidesert to forest. Elephant shrews have large eyes and ears and are further distinguished by their extremely long, narrow snout. These animals forage on the ground using their mobile snouts and long-clawed front feet to search for small invertebrates.

Hedgehogs are mainly nocturnal animals and predominantly insectivorous, although they have been known to feed on carrion and small mammals. They hibernate in winter because it is difficult for them to find and digest enough food to combat the cold.

Flying lemurs

The two surviving species of flying lemur (also known as colugos) represent an early specialized development of the basic insectivore type. These Southeast Asian tree-dwelling mammals resemble true lemurs, but are not related to them. They also are not really able to fly, but they glide among the treetops by means of membranes at the sides of the body. These membranes extend from the neck to the front feet, the hind feet, and the tip of the tail. Normally held folded in at the sides, the membranes become parachutelike when the animal extends them by stretching out its limbs. Flying lemurs are excellent climbers, and because they are nocturnal, they spend the day hanging by their clawed feet from a branch. At night they glide from tree to tree, feeding on leaves, buds, flowers, and fruit. Their jaw is unusual among mammals in that its lower incisors have become “comb teeth” and are used for grooming the fur. The comb teeth are similar to those of the lemurs.

Bats

The bats are second only to rodents in terms of number of species, more than 900 of which are known from almost all parts of the world. Their order, Chiroptera, is divided into two suborders. The suborder Megachiroptera contains one family, known as fruit bats, which feed primarily on fruit. Microchiroptera contains the other 17 families, most of which are largely insect-eating.
The main reason for the enormous ecological diversity of bats is their use of an otherwise unoccupied ecological niche their ability to capture nocturnal insects in flight. No other mammal can actively fly, and no other creatures, even birds, can surpass the bats’ mastery of the night skies. This agility is achieved by their sonar sensory system for navigation and prey-finding. To enable them to fly, bats have evolved extensive wings that consist of thin skin flaps stretched between the elongated fingers of the hands and between the forearm and the smaller hind legs. In most species, the skin flap also extends backward from the legs to the tail. The skin is an extension of the back and belly. In flight, bats can maneuver exceptionally well.

When bats alight, they hang upside down from perches with the aid of clawed hind feet. Some bats feed on the nectar and pollen of night-flowering plants and are important pollinators of those plants. Others feed primarily on fruit. For these species, flight enables them to travel long distances between fruiting or flowering trees. Other bats feed on small invertebrates and mammals and even capture fish in swoops to the water surface. The vampire bats (Desmodontidae) use their sharp, triangular-shaped front teeth to cut a narrow groove into the skin of sleeping mammals and birds and to sever capillaries, which bleed freely. They lap up the blood that flows from these wounds, consuming about 1 tablespoon (15 milliliters) of blood a day.

The three-toed sloth is found in the Amazonian forests, where it feeds on leaves and rarely descends to the ground. Its three digits are internal for almost their entire length. Only the long, curved claws protrude from the skin.

Armadillos, anteaters, and sloths

The order Edentata today contains about 30 species in three families: armadillos (Dasypo-didae), anteaters (Myrmecophagidae), and sloths (Bradypodidae). All have a reduced number of teeth, or none at all. And although the sloths are grouped with the insect-eating armadillos and anteaters, they are completely herbivorous that is, they feed only on plants.

The 20 species of armadillo of the Americas are nocturnal and feed primarily on insects, which they lick up with their long, narrow tongue, as well as other small invertebrates and vertebrates and, in some cases, carrion. Their limbs are sturdy and powerful, with large strong claws. Because armadillos have only a few small teeth set well back in their mouths, they cannot bite in self-defense. Instead, their bodies are protected by a shell made up of bands of bony plates, leaving only the limbs and underside vulnerable to attackers. Two species of armadillo curl up into a ball to protect these parts of the body.

Anteaters, with their long, toothless snout and long, sticky tongue, are highly specialized for feeding on ants and termites. Four species of anteater live in Central America and South America. The largest of them, the giant anteater, grows to more than 6 feet (1.8 meters) long. The giant anteater is grounddwelling, but the other species spend at least some of their time in the trees. The collared anteater, ortamandua, wraps its long tail around tree branches while feeding on ants and termites so that it will not fall.

The five species of sloth are so adapted to life in the trees that they can barely move on land. For this reason, they rarely descend to the ground, as they would make easy prey. They live in forests in Central and South America and spend much of their time hanging upside down from their large hooklike claws. There are two genera: Bradypus, the threetoed group, and Choloepus, which are twotoed. The three-toed species tend to be slower than the two-toed, and their grooved hairs carry algae, which give them a green color.

The tamandua, or collared anteater, is a mainly nocturnal, tree-dwelling species found in South America. Its body length reaches 23 inches (58 centimeters). This animal walks on the outside of its hands to prevent the tips of its curved claws from digging into its palms.

Pangolins

The pangolins (order Pholidota), or scaly anteaters, of Asia, Indonesia, and Africa lead a life similar to that of the American anteaters. They have no teeth and feed largely on termites, ants, and other insects, which they capture with delicate movements of their long tongue. The largest pangolin can extend its tongue 16 inches (40 centimeters) out of its mouth. Like anteaters, pangolins have a gizzardlike stomach that grinds down the hard exoskeletons of the insects they eat.

Pangolins are covered by a coat of horny scales resembling a coat of mail. When threatened, they roll themselves into a tight ball that few predators can pierce. Pangolins are shy creatures and move about at night.

Scaly anteaters, or pangolins, are distinguished by their scaly skin, which resembles the bracts of a pine cone. These arboreal mammals have a prehensile tail and a flexible body that can roll into a ball. Like the anteaters, they have strong claws for tearing open termite nests.