The insectivores are not seen so frequently as other mammals. They are shy and retiring animals; they are mostly active at night, frequenting places where abundant growths of vegetation serve to attract numerous insects. For the most part they are small-bodied creatures with elongated and mobile snouts and small eyes and ears. They possess musk, or scent, glands, from which a strong-smelling substance is secreted. Their toes are armed with very strong claws; certain species of insectivores use these claws as tools for burrowing into the earth.
The burrowing types of insect eaters, such as the moles, excavate a vast network of tunnels in the ground. The shrews and the hedgehogs, on the other hand, live above ground, though shrews sometimes use the tunnels made by mice. Tree shrews dwell almost entirely in trees; the African otter shrews, the water shrews and the water moles are particularly well fitted for an aquatic type of life. Most of the
insectivores supplement their staple diet of insects with worms, snails, lizards and small birds. Shrews often devour mice; otter shrews feed upon fish; hedgehogs and tree shrews consume fruit.
Though the insectivores make up only a small part of today's mammalian population, they are particularly interesting because they show us what some of the first mammals were like. Between 160,000,000 and 230,000,000 years ago, certain reptiles gradually evolved into the mammalian type of animal. The first mammals were quite small; they ate either insects or flesh and they lived in trees. Their small size and tree-dwelling habits undoubtedly helped them escape the attention of the formidable flesh eaters belonging to the dinosaur group. From this early mammalian stock several types of mammals evolved. One branch developed into the egg-laying mammals, such as the duck-billed platypus; another, into the pouch-bearing animals; still another, into the true insectivores. The bats, which still feast upon insects, were an early offshoot from these insectivores.
The insect eaters of today seem to have departed but little from their ancestors. It is true that the hedgehogs now have a coat of bristling spines and that the moles have gone underground to live; but their skeletal structure, teeth and small brains show typically primitive characteristics. Perhaps the shrews have changed least of all; they are still unspecialized, mouselike creatures. The tree shrews, which have larger brains than their relatives, are generally considered to represent a link between the insectivores and the primates, which include the lemurs, the monkeys and the apes.
The tree shrews, also known as tupaias, are now included in the order of Primates, to which man belongs. The name "insectivores" was first applied to the group by the great comparative anatomist Baron Georges Cuvier.
The characteristics
of the true insectívores
Though many animals, such as birds, fish, bats, frogs and snakes, eat insects, they are not all insectivores. The true insectivore is a mammal distinguished by the peculiar character of its teeth. These have the shearlike action of the typical carnivore, as opposed to the grinding action found in most other animals. In addition, the insectivore's teeth are furnished with sharp projections enabling the animal to seize and pierce the body of insects. Nearly all members of the order possess a long, narrow, mobile muzzle. The brain shows several primitive characteristics; large olf actory bulbs (extensions of the brain concerned with the sense of smell), few folded surfaces and an underdeveloped cerebrum. The cerebrum is well developed in the higher mammals, such as the apes. In man this portion of the brain is concerned with the thinking process.
It has been extremely difficult for zoologists to classify the insectivores. The taxonomist (one who classifies living things according to their natural order) looks for similarity of anatomical features when he tries to fit animals into a logical classification. When he deals with the insectivores, he finds that some types have retained many ancient, specialized features, while others have been profoundly modified through the ages.
According to the modern classification, the eight surviving families, arranged according to increasing specialization, are the Solenodontidae (including the solenodon of the West Indies); the Tenrecidae (great tenrec, aquatic tenrec, rice tenrec); the Potamogalidae (otter shrew); the Chrysochloroidea (golden mole of South Africa); the Erinaceidae (hedgehog, moonrat, gym-nura); the Macroscelidae (elephant shrew); the Soricidae (common shrew, pygmy shrew, short-tailed shrew or "mole" shrew, musk shrew, web-footed shrew); the Talpidae (desman, "shrew" mole, eared shrew mole, star-nosed mole, all the American moles).
The ancestor of the insectivores is believed to have been a hedgehog type. Its teeth and bones have been found in fossil deposits that date back to the Upper Cretaceous period, some 60 million years ago. At this time the climate was changing írom warm and humid to temperate and dry. The great reptiles disappeared, and the small, shy, warm-blooded creatures called mammals began to increase and multiply. Certain mammals (the bats) became aerial; some (the whales) became aquatic; others (the hoofed mammals and rodents) became plant eaters; still others (the cats, civets and wolves) became meat eaters. The insectivores, however, followed the ancestral mode of life and became even more specialized in it. Considering the fact that they survived for such a long period of time, the insectivores must have been astonishingly successful in adapting themselves to changes in climate and to the predacious (preying) habits of the carnivorous animals, their greatest enemies.
