_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.
[Illustration: _Photo by W. Saville-Kent, F.Z.S._] [_Croydon._
AUSTRALIAN FRUIT-BAT, OR "FLYING-FOX."
This photograph shows the "flying-fox" in its customary resting position. A
photograph of it flying is shown on page v of Introduction.]
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.
[Illustration: _Photo by Henry King_] [_Sydney._
AUSTRALIAN FRUIT-BATS.
In their roosting-places these bats hang all over the trees in enormous
numbers, looking like great black fruits. Although shot in thousands, on
account of the damage they do to fruit orchards, their numbers do not
appear to be reduced.]
[Illustration: _Photo by A. S. Rudland & Sons._
TUBE-NOSED FRUIT-BAT.
The tubular nostrils distinguish this and a species of insect-eating bat
from all other living mammals.]
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.
[Illustration: _Photo by Fratelli Alinari_] [_Florence._
PIPISTRELLE BAT.
This is one of the commonest of the British bats. It is the first to appear
in the spring, and the last to retire at the fall of the year.]
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.
[Illustration: _Photo by A. S. Rudland & Sons._
LEAF-NOSED BAT.
The leaf-nosed are the most highly organised of all the bats. The
remarkable leaf-like folds of skin around the nose or chin, as the case may
be, serve as delicate organs of perception. There are numerous species of
leaf-nosed bats.]
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.
[Illustration: _Photo W. Saville-Kent, F.Z.S._] [_Croydon._
COBEGO.
Back view of the cobego, with the limbs extended, showing the great size of
the flying-membranes, or parachute.]
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.
[Illustration: _Photo by W. Saville-Kent, F.Z.S._] [_Croydon._
COBEGO.
Vertical (front) view of the cobego, with newly born and naked young
attached. Note the extension of the membrane between the toes of the fore
feet of the adult.]
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.
[Illustration: _Photo by W. Saville-Kent, F.Z.S._] [_Croydon._
COBEGO ASLEEP.
All four limbs are used in suspending itself when asleep, as in the sloths.
In this position the cobego closely resembles, and is mistaken by its
enemies for, the fruits of one of the native trees. It is a nocturnal
animal.]
[Illustration: _Photo by L. Melland, F.Z.S._] [_North Finchley._
THREE BABY HEDGEHOGS.
Young hedgehogs are born blind and naked. The spines on their first
appearance are quite soft; they soon harden, and at the same time the power
to roll the body up into a ball is acquired.]
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.
[Illustration: _Photo by A. S. Rudland & Sons._
COMMON MOLE.
Note that this mole is changing its coat.]
[Illustration: _Photo by W. Saville-Kent, F.Z.S._] [_Croydon._
COMMON MOLE.
The skeleton is here revealed by the Röntgen rays.]
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.
[Illustration: _Photo by A. S. Rudland & Sons._
GOLDEN MOLE.
This is found only in South Africa. The name is derived from the wonderful
metallic lustre of the fur: the brilliancy of the hues is intensified by
immersion in spirit.]
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.
----