CHAPTER X.

_THE BATS AND INSECT-EATING MAMMALS._

BY W. P. PYCRAFT, A.L.S., F.Z.S.

These two groups are really closely allied; but the bats are generally considered apart, on account of their totally different mode of life. Originally, like their more commonplace relatives, they were dwellers upon the earth, or, more correctly, among the trees. By gradual modification of the fore limbs, and a corresponding development of folds of skin attached thereto, and to the body, they have acquired the power of flight. The cobego, to be mentioned presently, gives us a hint of how this may have come about.

The bats are the only members of the Mammalia which possess the power of true flight. The so-called flying-squirrels do not rightly deserve this title, for they have no wings. The wings of the bat have been formed by modification of the fore limbs, the finger-bones having become excessively lengthened, so as to serve as a support to a thin web of skin extending outwards from the body, much as the ribs of an umbrella support the covering. The hand of the bat is therefore a quite unique organ.

The wing-membrane serves yet another purpose, for its sense of touch is exceedingly delicate, enabling even blind bats (for bats are not blind usually, as is popularly supposed) to avoid objects placed in their path. Some bats, however, appear to depend also in some slight degree upon hearing. The sense of touch is still further increased by the development of frills or leaf-like expansions of skin round the nose and mouth, and by the excessive development of the external ears. Delicate hairs fringing these membranes probably act like the "whiskers" of the cat.

Insect-eating bats inhabiting regions with a temperate climate must in winter, when food-supplies cease, either hibernate or migrate to warmer regions. The majority hibernate; but two species at least of Canadian bats perform extensive migrations, it is supposed to escape the intense cold.

The power of flight has made the bats independent of the barriers which restrict the movements of terrestrial animals, and accordingly we find them all over the world, even as far north as the Arctic Circle. But certain groups of bats have an extremely restricted range. Thus the Fruit-bats occur only in the warmer regions of the Old World, the Vampires in America, whilst some of the more common insect-eating forms are found everywhere. Those forms with a restricted distribution are, it should be noticed, all highly specialised--that is to say, they have all become in some way adapted to peculiar local conditions, and cannot subsist apart therefrom. It is the more lowly--less specialised--forms which have the widest geographical range. There are some spots, however, on the world's surface from which no bat has yet been recorded--such are Iceland, St. Helena, Kerguelen, and the Galapagos Islands.

THE FRUIT-BATS.

These represent the giants of the bat world, the largest of them, the KALONG, or MALAY FOX-BAT, measuring no less than 5 feet from tip to tip of the wing. The best known of the fruit-bats is the INDIAN FOX-BAT. Sir J. E. Tennent tells us that a favourite resort of theirs near Kandy, in Ceylon, was some indiarubber-trees, "where they used to assemble in such prodigious numbers that large boughs would not infrequently give way beneath the accumulated weight of the flock." An observer in Calcutta relates that they occasionally travel in vast hordes, so great as to darken the sky. Whether they are performing some preconcerted migration or bent only on a foray to some distant feeding-ground is a matter for speculation. These hordes are quite distinct from the "long strings" which may be seen every evening in Calcutta on their way to neighbouring fruit-trees.

One of the most remarkable of this group is the TUBE-NOSED FRUIT-BAT, in which the nostrils are prolonged into a pair of relatively long tubes. Strangely enough, a group of insect-eating bats has developed similar though smaller tubes. Except in these bats, such tubes are unknown among mammals. Their function is not known.

INSECT-EATING BATS.

The vast majority of the bats comprising this group feed exclusively on insects. Some, however, have acquired the habit of fruit-eating, like the true fruit-bats; and a few have developed quite ogre-like habits, for they drink blood--indeed, they subsist upon nothing else. This they obtain from animals larger than themselves.

Many of the bats of this group have developed curious leaf-like expansions of skin around the nose and mouth, which are supposed to be endowed with a very delicate sense of touch. In some, as in the FLOWER-NOSED BAT, the nose-leaf is excessively developed, forming a large rosette. The upper border of this rosette is furnished with three stalked balls, the function of which it is surmised is probably ornamental--from the bat's point of view. To our more æsthetic taste the whole effect is hideous.

Limited as is our space, we cannot pass over the SUCKER-FOOTED BATS. These are met with, strangely enough, in countries so far apart as Brazil and Madagascar. The suckers from which they derive their name, in the Brazilian species, are small circular, hollow disks, attached to the thumb and the sole of the foot, recalling the suckers of the cuttle-fish and brown water-beetle. By their means the animal is enabled to climb over smooth vertical surfaces.

A white bat is a rarity in the bat world. We cannot therefore afford to pass without mention the fact that Central and South America possess two species of WHITE BATS. This colour is probably developed for protection's sake, the bats being found nestling between the silvery leaves of a cocoanut-palm. Brilliant coloration, on the other hand, is by no means so rare. WELWITSCH'S BAT, for instance--a West African species--is remarkable for its gorgeous coloration, the colours being orange and black. An Indian species, known as the PAINTED BAT, is said to be so brilliantly coloured as to resemble a gorgeous butterfly rather than a bat.

Ugliness is more common than beauty amongst the bats, and perhaps the ugliest of all the tribe is the NAKED BAT of the Malayan region. It is absolutely repulsive. The skin is naked, save for a collar of hair round the neck; whilst on the throat it gives rise to an enormous throat-pouch, which discharges an oily fluid of a peculiarly nauseating smell. On either side of the body is a deep pouch, in which the young are carried--a very necessary provision, for they would be quite unable to cling to the body of the parent, as do the young of fur-bearing bats, on account of the naked skin.

Of the great group of the VAMPIRE-BATS we can only make mention of the blood-sucking species. These are natives of South America. It is to Dr. Darwin that we owe our first absolutely reliable information about these little animals. Before the account in his Journal, it was uncertain to which of the vampires belonged the unenviable distinction of being the blood-sucker. During the stay of the great naturalist in Chili one was actually caught by one of his servants, as evening was drawing on, biting the withers of a horse. In the morning the spot where the bite had been inflicted was plainly visible, from its swollen condition. These two species, it has been stated, "are the only bats which subsist entirely on a diet of blood, yet it is possible that ... some of the JAVELIN-BATS or their allies may on occasion vary their ordinary food with it."

THE INSECTIVORA, OR FLIGHTLESS INSECT-EATERS.

Some members of this group have departed from the traditional insect diet. Thus the cobego feeds upon leaves, a curious aquatic shrew--the Potamogale of West Africa--upon fish, and the moles upon worms.

The group has a very wide geographical distribution, but there are nevertheless large portions of the globe in which they are conspicuous by their absence. They are never found in Australia or South America. Madagascar, Africa, and the West India Islands produce the most remarkable forms.

THE COBEGO.

This is a peculiarly interesting animal, which lives in the forests of Sumatra, Borneo, the Malay Peninsula, and the Philippine Islands. It dwells among the trees, moving from one to another by taking flying leaps through the air, covering as much as seventy yards at a jump. Prodigious leaps like this would be quite impossible but for the fact that the animal, which is almost as large as a cat, is provided with a sort of parachute, formed by a broad web of skin stretched between the body on either side and the fore and hind limbs, and between the hind limbs and the tail.

SHREWS, HEDGEHOGS, AND TENRECS.

The variation in form presented by the members of this group is considerable. The most noteworthy examples of this variation are furnished by the pretty little squirrel-like TREE-SHREWS of India and Borneo and neighbouring lands, the mouse-like JUMPING-SHREWS of Africa, the HEDGEHOGS, the TENRECS, the elegant little MOUSE-LIKE SHREWS of almost world-wide distribution, and the WATER-SHREWS. Of these, hedgehogs and tenrecs have undergone the greatest transformation. By a curious modification of their original hairy covering they have developed a formidable armour of sharp spines. When alarmed, the former roll themselves up into a ball by the contraction of powerful muscles, and so present an almost impregnable armour to an enemy. Stoats and foxes, however, appear at least occasionally to succeed in overcoming this defence and making a meal of the vanquished.

Tenrecs are found in Madagascar. The COMMON TENREC is the largest of all insect-eaters, and one of the most prolific, as many as twenty-one having been produced at birth. Of all living mammals it is the one most nearly allied to the Marsupials.

THE MOLES.

The COMMON MOLE shows a most perfect adaptation to its underground mode of life. The general form of the animal is long, cylindrical, and pointed in front, whilst the legs are exceedingly short, the foot only in the fore limb projecting from the body. This foot is very broad and spade-like and immensely powerful, its use being to force a way--often with incredible speed--through the soft, yielding soil, and not to support the body, as in running or walking. The hind feet are weak, but resemble those of its allies the shrews, for instance. The eyes have become reduced to mere vestiges, very difficult to find. The fur has become so altered in structure that it will lie equally smooth whether brushed towards head or tail, so that it should not be damaged when the animal travels backwards in its burrow. External ears have been dispensed with.

Worms form the staple diet of the mole, but besides underground insects of all kinds are greedily devoured. This animal is one of the most voracious feeders, falling ravenously upon its prey. It has been said with truth that so great is the ferocity displayed by the mole that if it could be magnified to the size of the lion it would be one of the most terrible of living creatures. That a constant supply of food is necessary to satiate its enormous appetite is shown by the fact that a mole will succumb to an abstinence of from ten to twelve hours. Moles fight among themselves furiously; and if two are confined together, the weaker will be attacked and devoured. They take readily to the water, and instances of moles observed in the act of crossing streams are numerous.

It is a curious fact, but the mole is unknown in Ireland; yet it ranges from England in the west through Asia to Japan.

Careful observation seems to have shown that with the common mole males are more numerous than females. Whether this is true of other species remains to be seen. The moles of North America form a group distinct from those of the Old World, though closely allied thereto. The WEB-FOOTED and the STAR-NOSED MOLES are the most interesting of the American forms.

Speaking of the prodigious speed with which these animals burrow their way through the ground, Dr. Hart Merriam remarks that in a single night, after rain, they have been known to make a gallery several yards in length, and that he had himself traced a fresh tunnel for nearly a hundred yards. As he says, we can only appreciate the magnitude of this labour by comparison, and "computation shows that, in order to perform equivalent work, a man would have to excavate in a single night a tunnel thirty-seven miles long, and of sufficient size to easily admit of the passage of his body."

The star-nosed mole is peculiar in that its nose is surrounded by a ring of finger-like processes, forming a kind of rosette, which probably acts as a highly sensitive organ of touch; furthermore, it differs from other moles in the great length of its tail, which is nearly as long as its body. Like the mole, this species makes its way through the ground with great speed.

Beneficial as moles undoubtedly are in destroying worms and obnoxious insects, yet they are regarded as a pest both by the farmer and gardener. That there is some justification for this dislike must be admitted; for the farmer suffers in that, in the search for food, crops are damaged by cutting through the roots of plants--the gardener not only for the same reason, but also because the ridges and hillocks which they make in their course disfigure the paths and beds of a well-kept garden.

The nearest allies of the moles are the curious aquatic DESMANS of Russia, and the SHREWS, some of which are quite mole-like in form, owing to their having adopted a similar mode of life.

The BURROWING SHREWS are not the only forms in the great group which have assumed a mole-like shape, for allied to the hedgehog-like TENRECS is a remarkable animal known as the GOLDEN MOLE. The mole-like shape of the body of this animal is another instance of adaptation to a similar mode of life. The fore limb of the golden mole is provided with huge claws, which are used for digging purposes; the hand is not broadened out spade-like, as in the common mole, the claws rendering this unnecessary.

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