Part 51

=Ants= (_Formicidae_).--These familiar and intelligent diminutive creatures are perhaps the most interesting of all insects, owing to the extraordinary way in which they have become adapted to a great variety of modes of life. All are social, and a community typically consists of males, females, workers (of one or more kinds), and, it may be, soldiers. The first two are generally provided with wings, though those of the females are soon shed, but exceptions to this occur, and some species may have both winged and wingless individuals of one sex or the other. The first pair of jaws (mandibles) are well or even excessively developed, and possess unusually free powers of movement in accordance with the varied functions they have to perform. In many cases the females (including the workers) are provided with a sting.

Ants hatch out as helpless, limbless larvæ, which have to be fed and carefully attended, either by the fertile females or the workers, as the case may be. Feeding is rather a curious affair, for the nurse possesses a sort of pouch (crop) connected with her gullet, and this is used as a store from which nutriment can be squeezed up into the mouth. Adults can feed one another in the same way, as also the little beetles and other insects which are often found as guests in their communities.

WANDERING ANTS OF THE TROPICS

These ants are of highly carnivorous habits, and move about in large armies, devouring everything of animal nature that comes in their way. The fact that they are blind, or practically so, does not seem to interfere with their devastations. Some of the forms are common in the hotter parts of South America, while others, the “driver” ants, are well known in Africa, where criminals, it is said, are sometimes tied up in their path, to perish miserably, if speedily.

SLAVE-HOLDING ANTS AND THEIR SLAVES

Some ants press weaker species of their kind into unmerited captivity. In one familiar instance the relatively large oppressor (_Polyergus rufescens_) is of reddish color and well endowed in the matter of jaws, while the enslaved species (_Formica fusca_) is small and dark. Regular slave raids are made from time to time, when, after stubborn resistance, the pupæ and older larvæ of the weaker form are carried away to lead a life of bondage, to which, indeed, they take very kindly. This kind of social economy has indeed become an absolute necessity to the slavers, which have quite lost the power of feeding their own young, while some such species cannot feed themselves.

A most extraordinary state of things occurs in the case of a small kind of ant (_Anergates_) which possesses no workers of its own, but lives within the communities of another species (_Tetramorium cæspitosum_) entirely made up of workers.

Some ants, such as the little black species (_lasius niger_) common in gardens, use as part of their food a sweet fluid that exudes from plant lice (_aphides_), and keep these insects as we keep kine. The captives are fed, sheltered, and jealously guarded. Fenced enclosures are constructed for them on plants in the vicinity of the nest, with which they are connected by covered roads. During winter the fragile eggs of the plant lice are taken underground and sedulously cared for.

THE HARVESTER ANTS OF EUROPE, NORTH AFRICA AND NORTH AMERICA

A number of ants are known that construct extensive underground dwellings, in which they store seeds of various kinds. Some of the American species (_Pogonomyrmex_) may be even said to winnow their grain, for they carefully strip off the husks and deposit these on rubbish-heaps outside the nest.

Some of the seed-storing ants almost deserve the name of maltsters on account of the way they deal with their harvest. The human method of making malt is to allow the barley grains to germinate to a certain extent until the contained starch is converted into malt-sugar, when the process is arrested by scalding. In similar fashion ants permit germination to go on to a certain point, and then kill the seedlings by biting away the little shoots and roots. In this way a supply of the sweet food they love is secured.

Among the most interesting of ants are leaf-cutting forms (_Atta_) native to tropical America. They are associated in huge communities occupying complex underground dwellings, the sides of which are marked by mounds that may measure as much as forty yards round. The chief food consists of a kind of fungus (_Rozites gongylophora_), cultivated on bits of leaf, and treated in such a way that little white elevations are produced. It is these that the ants desire.

The chief duty of one set of workers is to collect the pieces of leaf required. To facilitate their operations, roads, largely underground, are constructed, which lead to suitable trees, and may be as much as twenty yards long, or more. Curved pieces of leaf are bitten out and carried back to the nest, where they are handed over to another set of workers, by them to be reduced to smaller fragments and made into mushroom beds.

WHERE AND HOW THE HOMES OF ANTS ARE BUILT

Ants live in dwellings of the most varied kind, many being underground. In a large number of species ant-hills are constructed of various loose materials, our common native wood-ant (_Formica rufa_) being a good example of this. An Asiatic ant (_Oecophylla_) constructs a summer-house of leaves in a curious fashion. The larva possesses silk-glands from which a sticky fluid exudes, hardening quickly on exposure to the air. Advantage of this is taken by the workers, for they hold larvæ in their jaws, and employ them as living gum-bottles, while the leaf-edges to be cemented are held in position by other workers.

Some South American ants construct hanging nests in trees, by which protection against floods is secured. Other ants in the same part of the world make curious homes which well deserve the name of “hanging gardens,” for they are mainly constructed of living plants, some of which have never been found in any other situation. The plants are cultivated and tended by the ants with which they are associated. The soldiers of certain ants (_Colobopsis_), which tunnel out homes in the wood of trees, play the part of living front doors. Every entrance to the nest is guarded by one of these hall-porters, its huge head not only exactly filling the aperture, but closely resembling the adjacent bark in appearance. If this curious door be touched by a bit of stick or a feather, it remains shut, but is immediately opened when stroked by the antennæ of a worker.

CURIOUS ANT GUESTS AND ASSOCIATES

Not only may ants of two or more kinds be associated together in the same dwelling, but a nest may also be tenanted by peculiar species of beetles (and other insects), spiders, mites, or other creatures. Many of these, especially the beetles, are fed and cared for by the ants, some of them for the sake of a substance which exudes from their bodies; others, perhaps, to serve as pets. The beetle-grubs are looked after as well as the adults; at least in the case of certain blind species.

On the other hand, certain ant-beetles not only steal food from the ants, but also devour their young. There can be no doubt that these curious associations are very ancient ones, for many species of beetles are found nowhere else. A kind of bristle-tail that lives in ants’ nests is a thief pure and simple. It has been seen to steal the drops of honey being passed from the mouth of one worker to another, afterwards retreating at full speed.

The common red ant (_Myrmica rubra_) shelters and feeds a curious kind of blind mite, which lives on the bodies of its hosts. By stroking its entertainers with its legs it makes known its need of nutriment, and such requests are never refused. Not impossibly some return may be made for these good offices.

One of the Indian ants (_Sima rufo-nigra_) lives on the bark of trees with a species of wasp (_Rhinopsis ruficornis_) and a kind of spider (_Salticus_), both of which closely resemble it in appearance. The three associates appear to be good friends, while wasp and ant sometimes engage in a friendly wrestle.

HOW ANTS COMMUNICATE WITH ONE ANOTHER

The complex life of an ants’ nest is a striking instance of order among apparent disorder. Each of the innumerable individuals discharges its special tasks without hesitation, unless unusual circumstances prove a hindrance. It would seem, therefore, that there must be some means by which any one can convey information to others. When two meet they frequently stroke one another with their feelers, and this perhaps serves the purpose of language.

THEIR REMARKABLE HABITS OF CLEANLINESS

Some wonderful facts are recorded concerning matters of personal cleanliness among ants, and has shown incidentally that these insects perform amazing feats of acrobatic skill without the least effort, and quite as matters of course. For example, an ant will often hang from a grass stem by the claws of one leg, while it combs its antennæ, cleanses its five remaining feet, or bends its head upwards to lick its abdomen and furbish the joints of its armor. Indeed, thanks partly to the wonderful flexibility of its “waist,” and still more to the tenacity of its muscles, an ant is able to assume and maintain almost any position that the need or fancy of the moment may prompt.

Many stingless ants, when fighting, first bite their adversary with their jaws, and then bringing the tip of the abdomen beneath the body, squirt formic acid into the wound.

=Bees.=--See Domesticated Animals.

=Bumble-bees.=--These common bees are large, somewhat clumsy-looking insects which live in communities including workers or imperfect females as well as ordinary members of the two sexes. The nests are constructed in holes in the ground or other sheltered places, and the establishment of a community is due in the first instance to the labors of a queen in early summer. She makes a number of waxen cells, stores them with honey and pollen, and afterwards feeds the larvæ when they have devoured these provisions. From the first (and several other), batches of larvæ workers are chiefly produced, which undertake the constructive and nursing work, until at last the queen has nothing to do but lay eggs. Males and other queens are reared from some of the eggs laid in late summer and early autumn.

=Wasps=, like bees, are either solitary or social, and it is only in the latter that workers exist. Solitary wasps construct small nests of clay and little stones, or else make burrows. They possess the curious habit of storing up immature--for example, caterpillars--or mature insects, or even spiders, for the benefit of their larvæ when these hatch out. The kind of victim depends upon the species of the wasp concerned, but in any case it is killed or paralysed by stinging.

Social wasps somewhat resemble social bees in their habits, but their building material, instead of being wax, is a kind of paper made of chewed wood mixed up with saliva. In some instances the nest is suspended from a bush or tree, and is provided with a kind of overhanging roof by which rain is drained off.

In our commonest species, an underground site is chosen, and a series of combs constructed from above downward, the whole being enclosed in several layers of wasp paper. Adjacent combs are held together by little pillars. The young are at first fed upon fruit-juice, nectar, and other vegetable matter, for which a more stimulating diet of chewed insects is afterwards substituted.

The HORNET (_Vespa crabro_) is a social wasp which commonly nests in hollow trees or constructs elaborate nests out of wood fibers, suspended from boughs. The females have formidable retractile stings. The hornet is represented in the United States by the white-faced hornet (_V. maculata_), also a large species.

=FLIES= (_Diptera_)

There are some thirty or forty thousand species of flies known, while no other order has so many individuals as this. This enormous assemblage of insects, most of which are small or even minute, includes many species that have earned an undesirable reputation as bloodsuckers and pests. Except in fleas and a few others, such as sheep-ticks, there are two membraneous front wings, the hinder pair serving as sensory structures. The mouthparts of the female are very often piercing and sucking organs of great efficiency, the first and second jaws being in the form of slender lancets protected above and below by the upper and under lip respectively.

But in other types, such as the house-fly (_Musca domestica_), the jaws are modified into a proboscis used for sucking juices, and devoid of powers of perforation.

THEIR UNCLEANLY AND DEATH-CARRYING HABITS

This fly lays its eggs in manure or other refuse, these hatching out, passing through all their stages and emerging as perfect insects in a few days. Their uncleanly habits make the house flies most efficient agents in the carriage of different diseases, especially typhoid fever and others which attack the digestive tract. Flies are therefore not merely a nuisance to be deplored, but a positive danger to mankind. Among other flies are the carrion flies, black flies, the gnats and the mosquitoes, all troublesome to man, while others attack various plants.

THE LARGE VORACIOUS FLEAS

Of these the breeze-flies or gad-flies possess powerful piercing mouth-parts, with which they torment both stock and human beings. A well-known species is the long brown clegg (_Hæmatopota pluvialis_), often met with in woods. In some tropical kinds the jaws are of enormous length.

Robber-flies are voracious and insatiable forms which prey upon other insects, even wasps and tiger-beetles being among their victims.

Hover-flies are swift and elegant insects which have already been mentioned in connection with flowers. Some of them closely resemble bees in appearance.

The dreaded tsetse fly (_Glossina morsitans_), so fatal to horses in parts of South Africa, belongs here. Germs of the fly-sickness (_Nagana_) are introduced into the blood of the victims, Tsetse flies of other species are responsible for “sleeping sickness,” which makes parts of tropical Africa uninhabitable.

THE PESTIFEROUS MOSQUITOS AND GNATS

These are particularly notable for the blood-sucking propensities of the female. Some tropical mosquitoes disseminate the germs of such diseases as malarial fever. Wholesale destruction of the early stages, by pouring petroleum on the surface of the stagnant water in which they live, has been employed with conspicuous success at Havana and in the Panama Canal zone as a preventive measure against yellow fever and malaria.

Midges are very minute gnats, of which the aquatic larvæ are known as blood-worms.

THE WINGLESS FLEAS AND OTHER PESTS

Fleas are wingless members of the order, and their agility fully compensates for the loss of the power of flight. There are many species, infesting different mammals and birds. The females of the tiny sand-fleas, or chiggers (_Sarcopsylla penetrans_), of America deposit their eggs in the feet of human beings (or other animals), and unless the painful swellings thus brought about are carefully treated they are apt to fester dangerously.

=STRANGE ANIMAL FORMS FOUND IN THE SEA=

_STARFISHES AND SEA-URCHINS_ (_Echinoderms_)

=HEDGEHOG SKINNED ANIMALS OF THE SEA. SEA-LILIES, STAR FISHES, BRITTLE STARS, SEA URCHINS, AND SEA CUCUMBERS=

Echinoderms, or hedgehog-skinned animals differ from all the forms so far considered in the nature of their symmetry. Instead of being two-sided, with a well-marked distinction between right and left and front and back (bilateral symmetry), they resemble a star or regular flower in shape. The skin is hardened by the deposition of salts of lime, and the body is often covered with spines, as more particularly in sea urchins.

Five existing subdivisions are recognized: (1) Sea-lilies and feather-stars (_Crinoidea_); (2) Starfishes (_Asteroidea_); (3) Brittle Stars (_Ophiuroidea_); (4) Sea urchins (_Echinoidea_); and (5) Sea-cucumbers (_Holothuroidea_). All are marine.

=Sea Cucumbers= are sort of second cousins to the sea urchins and rather more distantly related to the starfish. As the name indicates, they are shaped like a cucumber, and hundreds of little feet on the side heighten the resemblance, as they recall the spines on the vegetable. Inside they have a coiled intestine, usually filled with mud and the contained vegetable and other debris. With us no use is made of the animals, but they are taken in great numbers in the South Seas, and sent to China, where, as trepang, they form an ingredient in soups.

=Sea-lilies= are deep-sea animals, once numerous and flourishing, but now comparatively rare, and only to be obtained by dredging in the deeper parts of the ocean. They are fixed by a long, jointed stalk bearing circlets of sensitive threads and terminating in a cup, in the center of which the mouth is situated. Radiating from the edges of the cup are five branching, feather-like arms, all of which are grooved above, the grooves uniting, and finally converging to the mouth. They are beset with cilia, and minute organisms are conducted inward along them to serve as food.

=Sea Urchins= are radiated animals which are usually shaped like a flattened sphere. They have a mouth, surrounded by five chisel-shaped jaws at one pole, while the whole outer surface is covered with slender, movable spines. Between the spines are numbers of slender, flexible, tubular feet, which pull the body along, while the spines act more like true feet. The animals feed mostly on seaweeds. They have no economic value with us, but in Europe the eggs of some species are eaten, forming part of the _frutti di mare_ of every Italian seaport.

=Starfishes.=--Starfishes are among the most familiar objects of the seashore, and the commonest kinds, such as the five-finger (_Asterias rubens_) and the comb-star (_Astropecten aurantiacus_) possess five radiating arms. The mouth is in the center of the under side, and leads into a capacious stomach, of which the first part can be protruded from the body to surround such prey as mussels and oysters.

A starfish crawls slowly by means of numerous tube-feet, which are lodged in five grooves radiating from the mouth, and make up a part of the water-vascular system, so called because it is full of sea-water. At the end of each arm is an unpaired tube-foot acting as a feeler, while on its under side there is an orange-red eye-spot.

The water-vascular system assists in breathing. It was probably first evolved in the interests of respiration, and this is its chief use in the sea-lily. Some of the spines are formed of little, two-bladed pincers, which clean the surface of the body.

Starfishes are remarkable for their powers of restoring lost parts. A detached arm can grow a fresh disc and another four arms.

_ANIMALS THAT APPROACH THE SIMPLEST FORMS OF LIFE_

WORMS, LEECHES, SEA-ANEMONES, CORAL-POLYPS, JELLY-FISHES, SPONGES

Several groups of the lower animals are collectively known as Worms, though most of these groups are but remotely related. Ringed worms are elongated creatures in which the body is made up of a considerable number of rings or segments, most of which are, on the whole, much alike. There is often a well-marked head, but no distinct thorax and abdomen, as in an insect or crayfish. Two subdivisions are recognized: (a) Bristle-worms (_Chætopoda_) and (b) Leeches (_Discophora_).

=Bristle-worms= include a host of marine worms, together with some that live in fresh water, and also the earthworms. Their average characters are best understood by examining one of the commonest shore-worms, known as the sea-centipede (_Nereis_). Here the segments are very clearly seen, and almost every one of them bears a pair of unjointed conical foot-stumps, used for crawling.

Imbedded in the foot-stumps of the sea-centipede are bundles of strong bristles, which give a hold on the underlying surface and prevent slipping. The head-region is fairly distinct, and bears a number of feelers of various kinds, as well as four simple eyes. Sea-centipedes and many of their allies are highly carnivorous, and seize their prey by means of a pair of horny jaws which can be protruded at will.

=Earthworms= are found in all parts of the world, though naturally they do not thrive in arid tracts; and their effect upon the fertility and drainage of the soil can hardly be calculated. Burrowing into the ground, they cast up the earth they have swallowed, and so pursue a constant and thorough system of ploughing. Though eyeless, they evade the light and only come out of their burrows at dusk, often remaining, even then, with their tails in the holes and their bodies working round and round.

Darwin long since demonstrated, the earthworm is one of the farmers’ best friends. Its burrows drain and aerate the soil, while the earth which has passed through its body is finely divided and constantly being brought to the surface from lower levels.

Not far from the front end of an earthworm a thickening will be seen, often erroneously supposed to be the result of injury. From it exudes a fluid which hardens into the egg-cases.

=Leeches= live in the sea, fresh water, or even in damp, tropical forests. The flattened body of the leech is divided by grooves into a number of narrow parts, several of which go to make up a segment. Foot-stumps and bristles are entirely absent, and progression is effected by means of suckers, one at each end. They effect a looping movement, but the animal can also swim by undulations of its body. The freshwater leech is a bloodsucking parasite. The mouth is situated in the middle of the front sucker, which serves to fix the animal to its victim. Three saw-edged jaws are then brought into play, a three-rayed cut being made, and a fluid poured out which prevents the blood from clotting. Digestion is slow, and the food is stored in a large crop, drawn out into numerous pairs of pouches. The head possesses eye-spots, but no feelers.

=ANIMALS LIKE PLANTS= (_Cœlenterata_)

of which sea-anemones, corals, and jelly-fishes are examples, are distinguished by the ray-like symmetry of starfishes and their kind, though here, as a rule, it is more perfect. In structure they are much simpler, than any of the animals so far considered. For such a creature is to all intents and purposes simply a stomach, the wall of which is made up of two layers of cells, one (_ectoderm_) external, and the other (_endoderm_) internal. In higher animals a third layer (_mesoderm_) is interposed.

=Sea Anemones= are common between tides and lower on all coasts. They are cylindrical animals, with a mouth surrounded by tentacles at one end. Inside there is a single cavity which serves as a stomach and whose branches run to all parts of the body, thus distributing the food like a blood vessel. The colors, especially in the tropics, are variable, and often gorgeous.