CHAPTER IXANT ARMIES—A SNAKE’S PRECAUTION—WONDERFUL BRIDGES AND TUNNELS—MUSHROOM-GROWING ANTS.
ANT ARMIES—A SNAKE’S PRECAUTION—WONDERFUL BRIDGES AND TUNNELS—MUSHROOM-GROWING ANTS.
We will next consider the foraging ants of such tropical countries as Brazil and Western Equatorial Africa. To the latter the name of driver-ants has been given, because when they set out on their invading marches they drive every living thing, including man, before them. Everything they seize they devour, and as they go in great numbers and constantly open out into two or more columns so as to enclose patches of the forest, hosts of creatures find it impossible to escape destruction. Du Chaillu gives an interesting account of these ants, which were calledbashikonayby the natives amongst whom he was living. He says: “This ant is very abundant in the whole region I have travelled over in Africa, and is the most voracious creature I ever met. It is the dread of all living animals from the leopard to the smallest insect. I do not think they build a nest or house of any kind. At any rate, they carry nothing away, but eat all their prey on the spot. It is their habit to march through the forests in a long regular line—a line about two inches broad, and often several miles in length. All along this line are larger ants, who act asofficers, stand outside the ranks, and keep this singular army in order. If they come to a place where there are no trees to shelter them from the sun, whose heat they cannot bear, they immediately build underground tunnels, through which the whole army passes in columns, to the forest beyond. These tunnels are four or five feet underground, and are used only in the heat of the day, or during a storm. When they grow hungry, the long file spreads itself through the forest in a front line, and attacks and devours all it overtakes with a fury which is quite irresistible. The elephant and gorilla fly before this attack. The black men run for their lives. Every animal that lives in their line of march is chased. They seem to understand, and act upon, the tactics of Napoleon, and concentrate, with great speed, their heaviest forces upon the point of attack. In an incredibly short space of time the mouse, or dog, or leopard, or deer is overwhelmed, killed, eaten, and the bare skeleton only remains.”
These terrible insects travel night and day. “Many a time,” says Du Chaillu, “have I been awakened out of a sleep and obliged to rush from the hut and into the water, to save my life, and after all, suffered intolerable agony from the bites of the advance-guard, who had got into my clothes. When they enter a house they clear it of all living things. Cockroaches are devoured in an instant. Rats and mice spring round the room in vain. An overwhelming force of ants kills a strong rat in less than a minute, in spite of the most frantic struggles, and in less than another minute its bones are stripped. Every living thing in the house is devoured. When on theirmarch the insect-world flies before them, and I have often had the approach of a bashikonay army heralded to me by this means. Wherever they go they make a clean sweep, even ascending to the tops of the highest trees in pursuit of their prey. Their manner of attack is an impetuous leap. Instantly the strong pincers are fastened and they only let go when the piece gives way. At such times this little animal seems animated by a kind of fury which causes it to disregard entirely its own safety, and to seek only the conquest of its prey. The bite is very painful.” This latter statement it is easy to believe from the figure given in Du Chaillu’s book of one of these driver, or bashikonay ants. It is drawn twice the size of the real insect, but, even so, this would make the latter at least as large as a wasp. The head is enormous, larger than the thorax and abdomen—which make the body—together, and from it a huge pair of curved and pointed mandibles project and cross each other at the tips. When fairly covered with such creatures the effect would be that of thousands of tiny pincers, all tearing out pieces of flesh at the same time. No wonder that the negroes who are naked, or nearly so, run for their lives. In old times, Du Chaillu tells us, native criminals used to be tied down in the path of these terrible ants, to be torn to pieces and devoured by them—a shocking piece of cruelty which one is glad to know even then (more than forty years ago) and amongst savages, was a thing of the past. This terrible fate, however, must sometimes overtake those who are too old or ailing to escape by their own efforts, and to assist whom there is no time, and possibly but little inclination.
But in spite of such catastrophes, and of the danger and inconvenience which these driver-ants cause to the negroes, they are yet, in reality, very useful to them, since, several times a year, their huts are freed from the vermin with which they at all times abound.
If the gorilla and elephant fly before these ants, one can understand that snakes, however large, would also be afraid of them; and accordingly we have a curious story told by the natives, of the anxiety felt by the great python lest he should be overtaken by their armies, whilst lying torpid after a meal, and of the means which he takes to avoid such a catastrophe. Having killed his prey by crushing it in the great folds of his body, he leaves it lying on the ground, and does not return until, having made a circle of a mile or more in diameter, about the body, he is assured that no ant-army is on the march. Only then does he dare to swallow his prey and risk the dangerous period of sluggish inactivity which is necessitated by the process of digestion. If, however, the object of fear should be met with the python glides off with all possible speed, leaving the booty to be devoured by the ants should they happen to come upon it.
The habit of these driver-ants of making a tunnel as they march along, and thus sheltering themselves from the heat of the sun, is very remarkable, but I cannot quite understand how they drive it so deep under the ground as Du Chaillu says. To do so must surely delay them for a very long time, and the quicker and more expedient course would seem to be to wait for the sun to go down, and then to cross the open space. However, we shouldnever assume, in natural history, that a certain course will be pursued by any animal, simply because it is the best one. Often, however obvious this seems, they act otherwise. From other accounts, however, it would seem as if the ants threw up their tunnel on the surface of the ground instead of excavating beneath it, and that, sometimes, the structure reared by them is more of the nature of an awning than a tunnel. The Rev. Dr. Savage, for instance, says: “If they should be detained abroad till late in the morning of a sunny day, by the quantity of their prey, they will construct arches over their path, of dirt agglutinated by a fluid excreted from their mouth. If their way should run under thick grass, sticks, etc., affording sufficient shelter, the arch is dispensed with; if not, so much dirt is added as is necessary to eke out the arch, in connexion with them.”
Sometimes a still more wonderful arch or tunnel is made by the ants, for it is a living one composed of the bodies of some of their number. These, apparently, stand in two rows upon their hinder legs, and by interlocking their jaws and intertwining their anterior legs and antennæ make a covered way for the workers to pass along. From this, it would appear that certain of the ants feel the heat less than the ordinary workers. Apparently, however, the ants only act in this way when the sky is clouded, and when, as a consequence, one would not have expected any covering to be necessary. Dr. Savage, who gives this interesting account of ant body-building, as one may call it, has not been sufficientlyexplicit in regard to the details and circumstances attending it.
More extraordinary even than their habit of making a living arch or gallery, is the method which these ants employ of passing rivers. To do this they climb a tree upon one or other of its banks, and running out along a branch overhanging the water, let themselves down by clinging one to another, until a rope is formed of their united bodies. This soon reaches the water, and becoming constantly longer as fresh ants run down and affix themselves, is swept out from the shore by the force of the current, until at length its free end is washed against the opposite bank. There is, now, a thin bridge of ants, like a ribbon and of immense length, stretched slanting-wise from shore to shore, and over it the main body of the ants ceaselessly pass, till there are no more to come. Only the bridge itself now remains, but the ants helping to form this, on the nearer side of the stream, detach themselves now from the tree, when the bridge changes to a rope in the water, and this, being carried at once down the stream, is soon washed against the further bank, to which its corresponding end is attached.[6]As soon as this has been accomplished, the living ants composing this organic work of engineering skill, crawl on shore and continue their march, bringing up the rear of the column. It has been asserted, I know—for I have read it somewhere, and well remember the accompanying illustration—that the monkeys inhabiting the Brazilian forests areaccustomed to cross the smaller rivers that flow through them, in the same way. As the ants do so, there seems nothing absolutely impossible in the thing, but as years have gone by and I have met with no reference to so interesting a fact in any work of standing, I have got to distrust the only authority I can remember for it—a boy’s book, namely, by Mayne Reid.
Du Chaillu, whose account of the driver-ants, or bashikonays, I have already quoted, describes their manner of bridging streams in a slightly different way, which, if correct, makes it still more remarkable. He says: “When, on their line of march, they require to cross a narrow stream, they throw themselves across, and form a tunnel—a living tunnel—connecting two trees or high bushes on opposite sides of the little stream, whenever they can find such, to facilitate the operation. This is done with great speed, and is effected by a great number of ants, each of which clings with its fore claws to its next neighbour’s body or hind claws. Thus they form a high, safe tubular bridge,throughwhich the whole vast regiment marches in regular order. If disturbed, or if the arch is broken by the violence of some animal, they instantly attack the offender with the greatest animosity.” This presents the matter in a still more interesting light, and as it is the account of a man who professes to have seen what he describes, it should rank, perhaps, before the other, which, though I have taken it from a trustworthy source, was not there given as a first-hand account. Both versions, however, may be correct.
If streams are not sufficient to daunt the driver-ant,neither are floods. When these occur, numbers of them rush together and cling to one another, forming a ball-shaped mass, that, being lighter than the water, floats upon it, till such time as the flood has retired. The size of these balls is, for the most part, that of an orange, but they may be either larger or smaller—tangerine orange-balls in the latter case. The natives say that the larger and stronger ants form the outer circumference of the globe, whilst the weakly ones—or, as they express it, the women and children—are contained and guarded in the centre.
I have never seen the real driver-ants, not having been in any really tropical country. In South Africa, however, I have often seen the armies, or, as the Kaffirs call them,impis, of a black, stinging ant, that seems to take their place. When these insects are disturbed in their march, the whole column makes a hissing noise, which can be very distinctly heard. How the sound is produced I do not know, but it is more like a hiss than anything else, and is accompanied, if I remember rightly, with a strong smell of formic acid. Though these black ants are fierce and bold, so that the Kaffirs admire them, call them warriors, and compare them with themselves, their marches are not attended with the striking sights which belong to those of the drivers, nor have they the wonderful habits or instincts of the latter. They are less than half their size, moreover, and their chief weapon being a sting, the mandibles are not extraordinarily developed. I never myself happened to be stung by one, but have heard others complain bitterly.
The driver-ants of Africa are represented in tropical America by theEcitons—a family containing numerous species—of which we have some interesting accounts by travellers who were, at the same time, naturalists. Speaking of theEciton drepanophora, Mr. Bates, in his well-knownNaturalist on the River Amazon, says: “When the pedestrian falls in with a train of these ants, the first signal given him is a twittering and restless movement of small flocks of plain-coloured birds (ant-thrushes) in the jungle. If this be disregarded until 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 in its tail and stinging with all its might. There is no course left but to run for it.” However, it is almost as easy to “fly from oneself” (a hard thing, Horace tells us) as from ants that have once crawled up beneath one’s garments and embedded their jaws in one’s flesh. Only after a halt, and special attention paid to each individual, are these to be got rid of, and then only by degrees, since these determined little warriors—all undecorated, and without even a thought of crosses or promotions—are content to let their bodies be torn from their heads, as long as they can leave the latter, with the jaws attached, sticking in the wounds they have made.
“The errand,” continues Mr. Bates, “of the vast ant armies is plunder, and wherever they move the whole animal world is set in commotion, and every creaturetries to get out of their way. But it is, especially, the various tribes of wingless insects that have cause for fear, such as heavy-bodied spiders, ants of other species, maggots, caterpillars, larvæ of cockroaches, and so forth, all of which live under fallen leaves or in decaying wood.” Unlike the bashikonay ants that we have been considering, these Ecitons do not ascend trees to any great height, so that young birds in their nests for the most part escape. Both species consist, like other ant communities, of males, females, and workers, but the differentiation of the latter into two castes, differing both in size and shape from one another, is most marked amongst the Ecitons. The members composing these two classes are known as the worker-majors and worker-minors respectively, and whilst the latter make up the majority of the host, and thus present the standard size and appearance, the former are much larger, with heads disproportionately big, and greatly lengthened jaws.
Both the African and American kinds hunt with method and system, and each species has its own particular way of setting to work. Of that employed by the one under consideration, Mr. Bates gives us the following account. “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 off, here and there, a thinner column, to forage for a short time on the flanks of the main army, and re-enter it again after their task is accomplished. If some very rich place be encountered anywhere near the line of march—for example, a mass of rotten wood abounding in insect larvæ—a delay takesplace, and a very strong force of insects is concentrated upon it. The excited creatures search every cranny, and tear in pieces all the large grubs they drag to light. It is curious to see them attack wasps’ nests, which are sometimes built on low shrubs. They gnaw away the papery covering, to get at the larvæ, pupæ, and newly hatched wasps, and cut everything to tatters, regardless of the infuriated owners which are flying about them. In bearing off their spoil in fragments, the pieces are apportioned to the carriers with some degree of regard to fairness of load: the dwarfs taking the smallest pieces, and the strongest fellows, with small heads, the heaviest portions. Sometimes two ants join together in carrying one piece, but the worker-majors, with their unwieldy and distorted jaws, are incapacitated from taking any part in the labour.”
The precise part in the life of the community which is played by these great worker-majors, with the relation which it no doubt bears to their superior size and modified shape, has long been a puzzle to naturalists. The first idea was that they formed a soldier caste—a natural supposition in view of their great armour-plated heads, and elongated twisted jaws. Observation, however, does not bear out this theory. The jaws, in spite of their size, are not so well adapted for seizing on a plane surface—the skin, for instance, of an animal—as are those of the smaller workers; and, moreover, these large ants seemed to Mr. Bates to be less pugnacious than the others. “The position,” he tells us, “of the large-headed individuals in the marching column was rather curious.There was one of these extraordinary fellows to about a score of the smaller class; none of them carried anything in their mouths, but all trotted along empty-handed and outside the column, at pretty regular intervals from each other, like subaltern officers in a marching regiment of soldiers. I did not see them change their position, or take any notice of their small-headed comrades marching in the column, and when I disturbed the line, they did not prance forth or show fight so eagerly as the others.” Mr. Bates then hazards a conjecture that these big ants may serve indirectly to preserve the community, by being indigestible to birds, and that their great, twisted mandibles may be effective, whilst lying in the crops or stomachs of the latter. This seems possible, since a certain number of unpalatable individuals in a community of ants might make birds disinclined to eat any of them. I think, myself, however, that it is premature to speculate on the part in life which these curiously modified worker ants may be designed to play, until we know something more of their home economy, and particularly of their architecture. This, it is true, is of a very rude kind, nor do these marauding ants appear to have any permanent place of abode. Still, they may do something in the shape of building, and the peculiar jaws of the worker-major class suggest that they are formed for seizing some special object, or performing some special kind of labour.
These foraging ants show a good deal of sympathy with one another, and if one is in distress the others will do their best to relieve him from his embarrassment. Mr. Belt, a naturalist who spent some time in Nicaragua,made some experiments with a view to testing these points. He took an ant, and placed it under a stone in the line of the marching column. The first of the marching ants that saw its plight hurried back, and soon returned with several companions, to whom it had evidently communicated the intelligence. Some seized and tugged the ant, whilst others bit and pushed the stone, and, between them, the prisoner was soon freed. Other ants Mr. Belt covered up with clay, leaving only their head or antennæ projecting, and all were rescued in the same way. Lord Avebury has tried similar experiments with our own English ants, but the results were not so satisfactory. Both in sympathy and intelligence, these foraging ants of America seem much superior to the various European species. More experiments, however, with a greater number of species are much to be desired.
Another ant of tropical America is the famoussaubaor leaf-cutting ant. All day long these insects seem occupied in cutting out pieces of leaves, and carrying them off to their nests. New arrivals in the country are astonished to meet long columns of them marching down well-beaten paths, and all carrying circular pieces of green leaf, the size of a sixpence, held upright in their jaws. All these are marching homewards, but beside them, empty-handed, another stream goes hurrying back to the forest, from which their comrades are returning laden. What use do the ants make of these leaves, after they have carried them down into their nests? In regard to this there have been various opinions. Some naturalists used to think that they used them as food simply, others thatthey made a sort of underground roof to their nests with them; but Mr. Belt has almost proved that what the ants really do with their leaves, is to make them into mushroom-beds, the mushrooms—not the leaves themselves—being used as food by the community. He found, on excavating their nests, that they consisted of a number of chambers, as large, and almost as round, as a man’s head. In each of these lay a brown mass of vegetable matter, which, on examination, proved to be made of the leaves themselves, now withered and cut into a number of small pieces, amidst which, and holding them all together, grew a minute white fungus—the mushrooms of the ants. Mr. Belt proved that it was not the leaves themselves which the ants ate, because he found deserted chambers filled with these, which, now that their manuring properties had become exhausted, no longer supported any fungus. Yet that the ants require food in their nests must be assumed, since they are never seen feeding outside them; and, moreover, when they desert the nest and establish themselves in another, they take the fungus-bearing leaves, but not the others, with them. Clearly, then, this fungus, which they cultivate themselves, must be their food—the ants are mushroom-growers.
Mr. Belt concludes his very interesting account of the sauba ants with one more instance of their intelligence. “A nest,” he tells us, “was made near one of our tramways, and, to get to the trees, the ants had to cross the rails, over which the waggons were continually passing and repassing. Every time they came along, a numberof ants were crushed to death. They persevered in crossing, for some time, but at last set to work and tunneled underneath each rail. One day, when the waggons were not running, I stopped up the tunnels with stones; but although great numbers carrying leaves were thus cut off from the nest, they would not cross the rails, but set to work making fresh tunnels underneath them. Apparently an order had gone forth, or a general understanding been come to, that the rails were not to be crossed.”