Popular Science Monthly/Volume 7/July 1875/Anent Ants

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THE

POPULAR SCIENCE

MONTHLY.

 

JULY, 1875.


 

ANENT ANTS.
By E. R. LELAND.

SINCE the earliest recorded observations of insect-life, the ant has been a subject of especial comment and wonderment. Found throughout the range of both temperate and the torrid zones, it is in the tropics that the most interesting species abound, and where their vast numbers and their industry and fearless pertinacity make them a veritable scourge.

Many confused, not to say fabulous, statements regarding them have been published in books of travels, and copied in natural history works; but enough has been recorded concerning them, which has the warrant of recent and high authority, to justify the views popularly held as to their intelligence and sagacity.

Mr. Bates, in "The Naturalist on the Amazon," devotes considerable space to them, and, in the descriptions following, very free use is made of his delightful book, and most of the illustrations are borrowed from that source.

One of the chief peculiarities of the ants is their social relations. Assembling in countless multitudes, they are divided into different classes, each with a special order of duties to fulfill, but all working harmoniously for a definite end—the perpetuation of the species. Their communities consist of males, females, and neuters; with generally two and sometimes three distinct orders or castes of the latter. Upon them devolves all the labor, the divisions being known as the worker-minors and the worker-majors, the brunt of the work falling upon the first, while the function of the worker-major, though not definitely understood, seems to be that of a superintendent or a soldier, or perhaps a combination of the two.

One of the most interesting of the American species is the saüba, or leaf-cutting ant [Œcodoma cephalotes). The workers of this species are of three orders, and vary in size from two to seven lines. Some idea of them may be obtained from the accompanying woodcut.

The true working-class of a colony is formed by the small-sized order of workers (1, Fig. 1). The two other kinds have enormously-swollen heads; in one of these the head is highly polished (2); in the other (3) it is opaque and hairy. The worker-minors vary greatly in size, some being double the bulk of others. The entire body is of solid consistence, and of a pale, reddish-brown color. The thorax, or middle segment, is armed with three pairs of sharp spines; the head also has a pair of similar spines proceeding from the cheeks behind.

PSM V07 D272 Leaf cutting ants.jpg
Fig. 1.—Saüba, or Leaf-cutting Ant.—1, Worker-minor; 2, Worker-major; 3, Subterranean Worker.

Their domes or outworks are very extensive, some of them being forty yards in circumference, but not more than two feet high. The entrances are small and numerous; in the large hillocks a great amount of excavation is required to get at the main galleries; the minor entrances converge at a few feet below the ground to one broad, elaborately-worked gallery or mine four or five inches in diameter. These underground abodes are very extensive. The Rev. Hamlet Clark relates that the saüba of Rio de Janeiro has excavated a tunnel under the bed of the river Parahyba, at a place where it is as broad as the Thames at London Bridge. At the Magoary Rice-Mills, near Pará, these ants once pierced the embankment of a large reservoir; the great body of water which it contained escaping before the damage could be repaired. One other fact is told of these ants, which shows the herculean nature of their labors. Their lives are dependent upon access to water, and they always choose places where it is to be obtained by digging wells. One case is related where a well was dug for domestic purposes, and water found at a depth of thirty feet; to do this, an ant-well was followed which was twelve inches in diameter.

The habit in this ant of clipping and carrying away immense quantities of leaves has long been recorded. When employed in this work, their processions look like a multitude of animated leaves on the march. They mount the trees in swarms. Each one places itself on the surface of a leaf, and cuts with its sharp, scissor-like jaws a nearly semi-circular incision on the upper side; it then takes the edge between its jaws, and, by a sharp jerk, detaches the piece which is about the size of a dime. Sometimes they let the leaf drop to the ground, where a little heap accumulates, until carried off by another relay of workers; but generally each marches off with the piece it has operated upon, and, as all take the same road to their colony, the path they follow soon becomes smooth and bare, looking like the impression of a cartwheel through the herbage. The heavily-laden workers troop up and cast their burdens on the hillock; another relay of laborers place the leaves in position, covering them with a layer of earthy granules, which are brought up one by one from the soil beneath. It has not been shown satisfactorily to what use the leaves are put. It was formerly supposed that they were consumed as food. Mr. Bates's investigations convinced him that the leaves were used to thatch the domes which cover the entrances to the subterranean dwellings, thereby protecting from the deluging rains the young broods in the nests beneath. Mr. Belt, however, who observed the leaf-cutting ants in Central America, and gives a full and interesting account of them in his "Naturalist in Nicaragua," arrives at the conclusion that the leaves which they gather in such enormous quantities are used to form beds for the growth of a minute fungus, on which they and their young live. Fritz Müller, writing from Brazil (Nature, vol. x., p. 102), says that he has always held this view, and that an examination of their stomachs under the microscope confirms it.

This ant is so abundant in some districts that agriculture is almost impossible, and wherever it exists it is a terrible pest. It is also troublesome to the inhabitants from its habit of plundering the stores of provisions in houses at night, for it is even more active by night than in the daytime.

The principal part of the visible work is done by the small-heads (1, Fig. 1), while those which have massive heads, the worker-majors (2), are generally observed to be simply walking about. They are not, in this species, soldiers, for they never fight. The function of superintendence would seem superfluous in a community where all work with precision. They cannot, however, be entirely useless to the community, for the sustenance of an idle class of such bulky individuals would be too heavy a charge for the species to sustain. Prof. Sennichrast, who studied some of the species of Œcodoma in Mexico, is of the opinion that their special rôle, if they have one, is borne in the excavation of the nest, and in tunneling the galleries, labors which require superior strength and better implements.

The third order of workers is the most curious. If the main shaft of a mine be probed, a small number of colossal fellows (3, Fig. 1) will slowly begin to make their way up the smooth sides of the mine. In the middle of the forehead is a trim ocellus, or simple eye, of quite different structure from the ordinary compound eye on the sides of the head. This frontal eye is totally wanting in the other workers, and is not known in any other kind of ant. Their special functions are unknown. None of this species are pugnacious.

The work of reproduction begins with the rainy season. The union probably takes place in the night, for in the morning the neighborhood of the nest will be strewed with the females, and the dead bodies of the males, the former already fertile, from whom the workers make it their duty to tear away the wings. The true females are incapable of attending to the wants of their offspring; and it is on the poor, sterile workers, who are denied all the other pleasures of maternity, that the care devolves. The successful début of the winged males and females depends likewise on the workers. Great activity reigns in an ants'-nest on the exodus of the winged individuals. The workers clear the roads of exit, and show the most lively interest in their departure, although it is highly improbable that any of them will return to the same colony. They are of large size, the female measuring two and a quarter inches in expanse of wing; the male is not much more than half the size. They swarm in vast numbers, but are so eagerly preyed upon by insectivorous animals that but few of the impregnated females escape the slaughter to found new colonies. An immense amount of labor would be saved to the ants, if, instead of raising annually myriads of winged males and females to perish, they raised only a few wingless males and females, which, free from danger, might remain in their native nests; and, as Fritz Müller says, he who does not admit the paramount importance of intercrossing must of course wonder why the latter manner of reproduction has not long since taken the place, through natural selection, of the production of winged males and females. But the wingless individuals would of course have to pair always with their near relatives, while by swarming a chance is given for the intercrossing of individuals not nearly related.

PSM V07 D274 Leaf cutting ant female.jpg
Fig. 2.—Saüba Ant, Female.

Resembling the saüba, in being vegetable-feeders, are the harvesting-ants (Atla stnictor, A. barbara, Pheidole megacephala etc.). It has been a fashion among naturalists to set down as pure invention the accounts by classical writers of the accumulation of cereals by ants for winter consumption, and to assume that the Biblical injunction to study the ways of her "who, having no guide, overseer, or ruler, provideth her meat in the summer, and gathereth her food in the harvests," was a figure drawn from careless observation; that ants, being carnivorous insects, would not eat dry, hard grains of wheat or barley, the idea that they would do so having arisen from mistaking the whitish cocoons which inclose the pupae for grains of wheat, to which they bear a resemblance. But Mr. Traherne Moggridge has recently, by careful observation in the south of Europe, confirmed in many of their minutest details the accounts given by ancient writers, and shown that, in treating these accounts with contempt, it is the modern authors who have been guilty of forming hasty conclusions from insufficient data.

The ants were described as ascending the stalks of cereals and gnawing off the grains, while others below detached the seed from the chaff and carried it home; as gnawing off the radicle to prevent germination, and spreading their stores in the sun to dry after wet weather. These statements Mr. Moggridge has verified, supplementing them by discovering the granaries in which they are stored, sometimes excavated in solid rock. He has seen them in the act of collecting seeds, and has traced seeds to the granaries; he has seen them bring out the grains to dry after a rain, and nibble off the radicle from those which were germinating; lastly, he has seen them feed, on the seeds so collected. A curious point is, that the collections of seeds, although stored in damp situations, very rarely germinate; yet nothing has been done to deprive them of vitality, for, on being sown, they grow vigorously. Their depredations are of such extent as must cause serious loss to cultivators.

Texas and Northern Mexico furnish a remarkable species in the honey-making ants (Myrmecocystus Mexicanus). The workers of their communities are divided into three classes: 1. Yellow workers, nurses and feeders; 2. Yellow workers, honey-makers; 3. Black workers, guards and purveyors.

The site chosen for their nest is usually some sandy soil in the neighborhood of shrubs and flowers, the space occupied being four or five feet square. The black workers surround the nests as guards, and are always in a state of great activity. They form two lines of defense, moving different ways, their march always being along three sides of a square; one column moving from the southeast to the southwest corners of the fortification, while the other proceeds in the opposite direction. Most of the nests lie open to the south; the east, west, and northern sides, being surrounded by the soldiers. In case of an enemy approaching, a number of guards sally forth to meet the intruder. Spiders, wasps, beetles, and other insects are, if they come too near the hive, savagely attacked, and the dead bodies speedily removed from the neighborhood, the soldiers at once resuming their places in the line.

Their object in destroying other insects is protection of the encampment, and not the obtaining of food. While one section of the black workers is thus engaged, a more numerous division will be found employed in entering the quadrangle by a diagonal line, bearing north-east, and carrying flowers and fragments of aromatic leaves, which they deposit in the centre of the square.

PSM V07 D276 Encampment of the honey making ant.jpg
Fig. 3.—Encampment of the Honey-making Ant (Myrmecocystus Mexicanus).

The line a of the sketch shows the path of this latter section, the mound of flowers and leaves being at c. This line leads to the shrubs, upon which another division of the black workers is settled, engaged in cutting off the leaves and petals to be conveyed to the nest. On the west side of the encampment is a hole marked d, leading to the interior of the nest. It is probably intended for the introduction of air, as, in case of any individuals carrying their loads into it, they immediately emerge and carry them to the common heap, as if conscious of having made a mistake. A smaller hole, near the southeast corner of the square, is the only other means by which the interior can be reached; and down this aperture, b, the flowers gathered by the black workers are carried along the line e from the heap in the centre of the square, by a number of the small yellow workers, who seem adapted for the gentler office of nurses for the colony within. No black ant is ever seen on the line e, and no yellow one ever approaches the line a, each keeping his own station, and following his given line of duty with a steadfastness which is remarkable.

When the course of the galleries is traced from the entrances, a small excavation is reached, across which is stretched, in the form of a spider's web, a net-work of squares about one-quarter inch across, the ends of the web being fastened firmly to the earth of the sides of the cell. In each one of the squares, supported by the web, sits one of the honey-making workers—prisoners, for locomotion is impossible, the distended abdomen which constitutes the honey-bag being at least twenty times as large as the rest of the body. The workers provide them a constant supply of flowers and pollen, which, by a process analogous to that of the bee, they convert into honey. Whether the honey-makers are themselves used as food, or excrete their saccharine fluid, and then proceed to distill more, is not known. Indeed, that the remainder of the inhabitants feed on the supply thus obtained in any manner, although surmised, has not been established, very little being known of the economy of these creatures.

The honey is much sought after by the Mexicans, who not only use it as a delicate article of food, but ascribe to it great healing properties.

The worst insect pest of tropical America is the terrible fire-ant (Myrmica sævissima), whose sting is likened to the puncture of a red-hot needle. It is found only on sandy soils in open places, and seems to thrive most near houses and in weedy villages. Towns are sometimes deserted on account of this little tormentor. It is a small species, of a shining red color, not greatly differing from the common red stinging-ant of our own country, except that the pain and irritation caused by its sting are much greater. Where it abounds, the whole soil is undermined by it; the ground is perforated with the entrances to their subterranean galleries, and a little sandy dome occurs here and there where the insects bring their young to receive warmth near the surface. Homes are overrun with them; they dispute every fragment of food with the inhabitants, and destroy clothing for the sake of the starch. All eatables have to be suspended in baskets from the rafters, and the cords well soaked with copaiba-balsam, which is the only means known to prevent them from climbing. They seem to attack persons out of sheer malice. The legs of tables, chairs, and stools, and the cords of hammocks, have to be smeared in the same way.

Belonging to a totally different group are the. Ecitons, or foraging-ants; they are carnivorous, and hunt in vast armies, exciting terror wherever they go, resembling in their habits the. often-described drivers of tropical Africa, though belonging to quite another subgroup of the ant tribe. They are composed, besides males and females, of two classes of workers—a large-headed and a small-headed class; the large-heads have, in some species, greatly-lengthened jaws; the small-heads have jaws always of the ordinary shape, but the two classes are not sharply defined in structure and function, except in two species. In these the jaws of the worker-majors are so monstrously lengthened that they are incapacitated for taking part in the labors of the worker-minors, and act as soldiers. The peculiar feature in the habits of the genus Eciton is their hunting for prey in regular bodies or armies. It is this which chiefly distinguishes them from the genus Myrmica, the common red stinging-ant of the temperate zone, whose habit is to search for food in the usual irregular manner. All the Ecitons hunt in large organized bodies; but almost every species has its own special manner of hunting.

Eciton Legionis.—In this species there is no division in classes among its workers, although the difference in size is very great. It lives in open places, and its movements are easy to be observed; its sting and bite are not very formidable. The armies consist of thousands of individuals, and move in rather broad columns. They are quick to break line on being disturbed, and attack hurriedly and furiously any intruding object. Their activity seems to be chiefly directed to plundering the nests of a large defenseless ant of another genus (Formica).

Eciton Drepanophara.—This, one of the commonest species of foraging-ants, confines its ravages to the thickest part of the forest. When a pedestrian falls in with one of their trains, the first signal given him is a twittering and restless movement of small flocks of plain-colored birds (ant-thrushes) in the jungle. If this be disregarded, and he advances a few steps farther, he is sure to fall into trouble, and find himself suddenly attacked by numbers of the ferocious little creatures. They swarm up his legs with incredible rapidity, each one driving his pincer-like jaws into his skin, and, with the purchase thus obtained, doubling its tail and stinging with all its might. There is no course left but to run for it. The tenacious insects then have to be plucked off, one by one, a task which is generally not accomplished without pulling them in twain, and leaving heads and jaws sticking in the wounds.

The errand of the vast ant-armies is plunder. Wherever they move, the whole animal world is set in commotion, and every creature tries to get out of their way. It is especially wingless insects that have cause to fear, such as heavy-bodied spiders, maggots, caterpillars, larvæ of cockroaches, etc., all of which live under fallen leaves, or in decaying wood. The main column, from four to six deep, moves forward in a given direction, clearing the ground of all animal matter, dead or alive, and throwing out here and there a thinner column to forage for a short time on the flanks of the main army. If some rich place be encountered, for example, a mass of rotten wood abounding in insect-larvæ, a delay takes place, and a very strong force is concentrated upon it. The excited creatures search every cranny, and tear in pieces all the grubs they bring to light. They attack wasps'-nests, when built on low shrubs, gnawing away the paper covering to get at the larvæ, pupæ, and newly-hatched wasps, and cut every thing to tatters, regardless of the infuriated owners which are flying about them.

PSM V07 D279 Foraging ants.jpg
Fig. 4.-Foraging-Ants (Eciton drepanophara).

The life of the Ecitons is not all work, however; they seem frequently to be employed in a way that looks like recreation. This always takes place in a sunny nook. The main column of the army and the branch columns are in their ordinary relative positions; but, instead of pressing forward eagerly and plundering right and left, they seem to be smitten with a sudden fit of laziness. Some walk slowly about; others brush their antennæ with their fore-feet; but the drollest sight is their cleaning one another. Here and there an ant may be seen, stretching forth first one leg and then another, to be brushed and washed by one or more of its comrades, who perform the task by passing the limb between the jaws and the tongue, finishing by giving the antennæ a friendly wipe. It is a curious spectacle, and well calculated to increase one's amazement at the similarity between the actions of ants and the acts of rational beings—a similarity which must have been brought about by different processes of development of the primary qualities of mind. The action of these ants looks like simple indulgence in idle amusement. Have these little creatures, then, an excess of energy, and do they expend it in mere sportiveness, like young kittens, or in idle whims, like rational beings?

Eciton Prædator.—This species differs from other Ecitons chiefly from its habit of hunting, not in columns, but in dense phalanxes consisting of myriads of individuals. A phalanx, when passing over smooth ground, occupies a space from four to six yards square. Nothing in insect-movements is more striking than this rapid march of these large compact bodies.

Blind Ecitons.—None of the foregoing kinds have eyes of the faceted or compound structure, such as are usual in insects, and which ordinary ants (Formica) are furnished with; but all are provided with organs of vision, composed each of a single lens. Connecting them with the utterly blind species of the genus, is a very stout-limbed Eciton, the E. crassicornis, whose eyes are sunk in deep sockets. This ant goes on foraging expeditions like the rest of its tribe, but it avoids the light, always moving in concealment under leaves and fallen branches. When its columns have to cross a cleared space, the ants construct a temporary covered way with granules of earth, arched over, and holding together mechanically; under this the procession passes in secret, the indefatigable creatures repairing their arcade as fast as breaches are made in it.

Next in order comes the E. vastator, which has no eyes, though the collapsed sockets are plainly visible; and, lastly, the E. erratica in which both sockets and eyes have disappeared, leaving only a faint ring to mark the place. The armies of E. vastator and E. erratica move wholly under covered roads, constructing them rapidly as they advance. The column of foragers pushes forward, step by step, under the protection of these covered ways, and, on reaching a rotten log, or other promising hunting-ground, pour into the crevices in search of booty. The grains of earth for their arcades are taken from the soil over which the column is passing, and are fitted together without cement.

PSM V07 D280 Foraging ants.jpg
Fig. 5.—Foraging-Ants (Eciton erratica), constructing a Covered Road—Soldiers sallying out on being disturbed.

Working in numbers, they build up simultaneously the sides of their convex arcades, and contrive in a surprising manner to approximate them and fit in the key-stone without letting the loose, uncemented structure fall to pieces. There is a very clear division of labor between the two classes of neuters in these blind species. When a breach is made in one of their covered ways, all the ants underneath are set in commotion, but the worker-minors remain behind to repair the damage, while the large-heads issue forth in a most menacing manner, rearing their heads, and snapping their jaws with an expression of fiercest rage and defiance. Pitched battles sometimes occur between different pugnacious species, and classical writers have deemed them worthy to be recorded. Kirby and Spence relate that "Æneas Sylvius, after giving a circumstantial account of one contested with great obstinacy by a large and a small species, adds that 'this action was fought in the Pontificate of Eugenius IV.'" Thoreau gives a graphic description—in his whimsical style of exalting small things and emphasizing the trifling difference that there is between big and little actors and events in Nature—of a similar engagement that took place near his hut "in the presidency of Polk, five years before the passage of Webster's Fugitive Slave Bill" ("Walden," p. 346).

Whether such an enactment obtains in any of the ant nations is unknown, but that certain of them possess the extraordinary instinct of capturing the pupæ of other species and bringing them up as slaves, is a well-authenticated fact. They are made captive while still in the cocoon, and on emerging become the auxiliary workers and friends of their captors, as though such was their natural destiny.

But no fanciful exaggeration is needed to impress us with the degree of forethought, methodical industry, and dauntless courage, the engineering and mechanical skill, the reasoning and perceptive powers and general sagacity which the ant displays.

If space permitted, numerous illustrative citations could be given. A member of the Natural History Society describes a tubular bridge, half an inch in diameter, and spanning a chasm twelve inches across. A correspondent of Mr. Darwin's, Mr. Joseph D. Hague, a geologist of California, submits what seems to be satisfactory evidence that they realize danger from seeing the corpses of their fellows, an inference drawn by no other invertebrate, if indeed it be by the higher animals.

They keep domestic animals. The aphides, or plant-lice, excrete a peculiar sweet fluid which the ant obtains by caressing the abdomen of the aphis with its antennæ. Ordinarily they seek the aphides upon plants, but that they also keep them in their nests much as man keeps cows, is an opinion which receives the sanction of eminent naturalists, among them Sir John Lubbock, who further says: "Ants also keep a variety of beetles and other insects in their nests. That they have some reason for this seems clear, because they readily attack any unwelcome intruder; but what that reason is we do not yet know. If these insects are domesticated by the ants, then we must admit that the ants possess more domestic animals than we do."

Indeed, their whole social economy is of a complex order. Nowhere is the division of labor—which in mankind always marks a high state of civilization—so rigid, being carried to the extreme of a physical modification of great numbers of the community for the better fulfillment of their duties. Their undeveloped sterile females may serve to warn—or to encourage—those members of the Anthropidæ who are so anxious to subordinate, if not wholly lay down, the gentle functions of maternity in order that they may engage in the sterner work of the world!

When, marking their size, we consider the mighty character of the works which they complete; when we reflect upon the infinitesimal ganglion which is the seat of the intelligence they display, we may well be filled with surprise, and almost wonder if man, or any other order of the vertebrata, is destined to remain forever the higher animal!