Popular Science Monthly/Volume 12/January 1878/Our Six-Footed Rivals II
|←Style|| Popular Science Monthly Volume 12 January 1878 (1878)
Our Six-Footed Rivals II
|Sketch of Professor Joseph Le Conte→|
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EVEN more wonderful than the mere intelligence of the ant is its power of organization—the point, probably, in which it approaches most closely to man. Suppose that ants, instead of forming nations, lived like most creatures, merely in pairs, each endeavoring to rear a young brood, who, when mature, would enter upon a similarly isolated career. Let them be as brave, as intelligent, and as strong, as they now are, still how humble and insecure would be their position! Against the attacks of the giant spiders, centipedes, hornets, and wasps of warm climates, they could make no effectual resistance. Prey, which in their present condition they easily secure, would escape them, or would scarcely even notice their puny efforts. In short, there is every reason to believe that many of their species would become extinct, and that the remainder would live, so to speak, mainly on sufferance, playing no appreciable part in the economy of the globe. Turning from this hypothetical survey of the ant as an individual, unorganized being to its actual condition, we see the most striking contrast. Mr. Belt gives the following graphic account of the excitement caused by a marching column of Ecitons in the primeval forests of Nicaragua: "My attention was generally first called to them by the twittering of some small birds belonging to different species. On approaching, a dense body of the ants, three or four yards wide, and so numerous as to blacken the ground, would be seen moving rapidly in one direction, examining every cranny and underneath every fallen leaf. On the flanks, and in advance of the main body, smaller columns would be pushed out. These smaller columns would generally first flush the cockroaches, grasshoppers, and spiders. The pursued insects would rapidly make off, but many, in their confusion and terror, would bound right into the midst of the main body of ants. At first, the grasshopper, when it found itself in the midst of its enemies, would give vigorous leaps, with perhaps two or three of the ants clinging to its legs. Then it would stop a moment to rest, and that moment would be fatal, for the tiny foes would swarm over the prey, and, after a few more ineffectual struggles, it would succumb to its fate, and soon be bitten to pieces and carried off to the rear. The greatest catch of the ants was, however, when they got among some fallen brushwood. The cockroaches, spiders, and other insects, instead of running right away, would ascend the fallen branches and remain there, while the host of ants were occupying all the ground beneath. By-and-by, up would come some of the ants, following every branch, and driving before them their prey to the ends of the small twigs, where nothing remained for them but to leap, and they would alight in the very throng of their foes, with the result of being certainly caught and pulled to pieces.
"The moving columns of Ecitons are composed almost entirely of workers of different sizes, but, at intervals of two or three yards, there are larger and lighter-colored individuals that often stop and sometimes run a little backward, stopping and touching some of the ants with their antennæ. They look like officers giving orders and directing the march of the column.
"The ants send off exploring-parties up the trees, which hunt for nests of wasps, bees, and probably birds. If they find any, they soon communicate the intelligence to the army below, and a column is sent up immediately to take possession of the prize. I have seen them pulling out the larvæ and pupæ from the cells of a large wasps' nest, while the wasps hovered about, powerless, before the multitude of the invaders, to render any protection to their young."
Still more formidable are the "driver-ants" of tropical Africa, so called because, on their approach, even the lion, the elephant, and the huge python, at once betake themselves to flight.
Nor are the purely vegetarian ants of less importance in the economy of the countries they inhabit. They decide, in a manner, what trees shall grow and what shall be exterminated, and it is only such as are comparatively distasteful to them that escape. In Nicaragua, they render the acclimatization of any foreign tree or vegetable a task of great difficulty. Mr. Belt was often told, on asking the reason why no fruit-trees were grown at certain places: "It is of no use planting them; the ants eat them up." These ants climb up the trees, when "each one, stationing itself on the edge of a leaf, commences to make a circular cut from the edge with its scissor-like jaws, its hinder feet being the centre on which it turns. When the piece is nearly cut off, it is still stationed upon it, and it looks as though it would fall to the ground with it; but, on being finally detached, the ant is generally found to have hold of the leaf with one foot, and, soon righting itself and arranging its burden to its satisfaction, it sets off at once on its return."
An observer, standing near the ant-hills, "sees from every point of the compass ant-paths leading to them, all thronged with the busy workers carrying their leafy burdens. As far as the eye can distinguish their tiny forms, troops upon troops of leaves are moving up toward the central point and disappearing down the numerous tunneled passages. The ceaseless toiling hosts impress one with their power, and one asks, 'What forests can stand before such invaders?' " Concerning the use to which the ant-leaves are put, some difference of opinion prevails; that they do not directly serve as food is admitted. Mr. Bates, from observations made in Brazil, concludes that "the leaves are used to thatch the domes which cover the entrances to their subterranean dwellings, thereby protecting from the deluging rains the young brood in the nests beneath." Mr. Belt, who has carefully examined the habits of an allied species in Nicaragua, believes that the real use they make of them is as a manure, on which grows a minute species of fungus on which they feed—that they are, in reality, mushroom growers and eaters. The reasons for this view are given in detail in Mr. Belt's work, and appear very satisfactory. But Mr. Bates's view may be correct also. In short, save man alone, there is no creature which can effect such widespread and profound alterations in the condition of a country as the tiny ant. It has been indeed mentioned in the Quarterly Journal of Science that the pig, the goat, and the rabbit, have succeeded in extirpating the natural flora, and consequently, to a great extent, the fauna, of certain islands, such as St. Helena. Yet this takes place only in countries where there are no carnivorous beasts, birds, and reptiles, to keep them in check. But in every warm and fruitful climate the ant is king. This power, we perceive, is not due to mere numbers; it is, in great part, the result of organization. Other species of insects are perhaps even more numerous, and, individually considered, as capable of destructive action; but locusts, potato-beetles, mosquitoes, noisome as they may be considered, are, in comparison with ants, what a promiscuous mob is in comparison with a well-trained and organized army. Each ant, like an experienced soldier, knows—whether rationally or instinctively it matters not—that it will be systematically supported by its comrades. What would be the prospects of agriculture in Western Asia, in Northern Africa, or in the Western States of the American Union, if the locusts, when engaged in desolating a field, were to attack, en masse, any man or bird who should interfere with them? But, on the contrary, they allow themselves to be slaughtered in detail, each indifferent to the fate of his neighbor.
Ants evince that close mutual sympathy which, to an equal extent, can be traced probably in man alone, and which has, in both these cases, proved one of the primary factors in the development of civilization. Had man been devoid of this impulse, he would have remained a mere wandering savage—perhaps a mere anthropoid, occurring as a rare species in equatorial districts. Without a similar impulse, the Ecitons would have ranked among the many solitary species of Hymenoptera. Of the mutual helpfulness of these same Ecitons, Mr. Belt gives us some most interesting cases which came under his own observation: "One day, when watching a small column of these ants (Eciton hamata), I placed a little stone on one of them to secure it. The next that approached, as soon as it discovered its situation, ran backward in an agitated manner, and soon communicated the intelligence to the others. They rushed to the rescue: some bit at the stone and tried to move it; others seized the prisoner by the legs, and tugged with such force that I thought the legs would be pulled off; but they persevered until they got the captive free. I next covered one up with a piece of clay, leaving only the ends of the antennas projecting. It was soon discovered by its fellows, who set to work immediately, and, by biting off pieces of the clay, soon liberated it. Another time I found a very few of them passing along at intervals. I confined one of these under a little piece of clay, with his head projecting. Several ants passed it, but at last one discovered it and tried to pull it up, but it could not. It immediately set off at a great rate, and I thought it had deserted its comrade; but it had only gone for assistance, for in a short time about a dozen ants came hurrying up, evidently fully informed of the circumstances of the case, for they made directly for their imprisoned comrade, and soon set him free. The excitement and ardor with which they carried on their exertions for the rescue could not have been greater if they had been human beings."
Such cases as these are of the greater moment because many other social and semi-social animals treat an unfortunate companion in a very different manner. It is on record that a rook, which had got entangled among the twigs of a tree, was pecked and buffeted to death by its neighbors, despite the efforts of its mate for its protection.
Facts are not wanting which show that the social organization of ants takes cognizance of sanitary matters. In Australia they have been known to bury their dead, not without some degree of formality according to their caste. In experimental formicaries in this country, ants have been observed to throw the bodies of their dead companions into the water surrounding their dwellings. In the nests of almost all species great care is taken to preserve cleanliness. The agricultural ant of Texas removes any offensive matter placed near its city, and will even take the trouble to carry away the droppings of cattle that have fallen on its cleared ground. Any dung-rolling beetle which brings its ball of ordure within these sacred precincts is at once attacked and put to death, and the nuisance is quickly cut to pieces and carried to a distance.
Nor are laws on other matters wanting. Ants who have, from some unknown cause, refused to work have been observed to be put to death. Among the agricultural ants, prisoners have been known to be brought in by a fellow-citizen and handed over in a very rough manner to the guards, who are always on duty on the level ground before the city, and who carry off the offender into the underground passages. What is his after-fate is not known. It is almost needless to point out that even the faintest rudiment of law proves the existence of some notions of right and wrong, as well as of a power of communication which must go into minute details.
We have now to deal with the great question whether the civilization of ants, like that of man, has been gradually and slowly developed by the accumulation of experience, or whether — as the believers in the fixity of habits and instincts still contend — it is primordial, coexistent with the species in all the details which we now observe. Direct historical evidence is here yet more difficult to obtain than as concerns animal structure. We smile, with just reason, at the French savants of the Egyptian Expedition, who imagined that, by the study of the animal-mummies there preserved, they might gain some light on, or rather find some argument against, the mutation of species. At the same time, we readily admit that, could we find a complete series of skeletons, anatomical preparations, or even photographs of the best-known animals, made at intervals of a century, and extending backward for say a hundred thousand years, the doctrine of evolution would be brought to a crucial test. But, concerning the former habits and instincts of animals, correct information is far more difficult to obtain. The "stone-book" is silent or oracularly vague. Even if we had written documents left us by some naturalist of the Miocene ages — if we can suppose such a being to have existed — what security should we have for the accuracy and the completeness of his researches?
To meet this difficulty an attempt, remarkable for its subtile ingenuity, has been made by Prof. Heer. He points out that, according to the reckoning of the most discreet geologists, at least a thousand centuries must have elapsed since Britain was severed from the Continent of Europe. For this long stretch of time, therefore, British animals must have been cut off from their representatives in France, Belgium, and Switzerland. If, then, the habits of a certain slaveholding ant (Formica sanguinea) in England are found identical, as he maintains, with the habits of the same species in Switzerland, there is a strong presumption that its economy has undergone no change for the last hundred thousand years. To this argument, we must reply that the isolation between British and Continental species of insects is by no means so complete as is here assumed. Winged ants travel very considerable distances, and, if our memory does not deceive us, have been met with out at sea. That a part of a swarm should he blown over from the French coast to England, or vice versa, is by no means improbable. And it is well known that if a party of working-ants fall in with an impregnated female of their own species, they immediately lead her to their nest and install her in a royal apartment. That there may have been within the last ten thousand—or even one thousand—years direct intercommunication of this kind between the slave-making ants of England and those of Switzerland, seems to us fully more probable than the contrary supposition.
Again, we may ask whether the conditions under which ants would be respectively placed in Switzerland and in England are not so closely analogous that their social development must proceed on parallel lines? In both they would encounter nearly the same climate, the same food, and the same enemies. Surely, therefore, a close correspondence in habits is no decisive proof of their immobility. But, after all, is there such an absolute accord between the habits of the Swiss and of the British ants as the validity of Prof. Heer's argument would require? Mr. Darwin thinks that in the nests of the British Formica sanguinea there is a relatively smaller proportion of slaves, which therefore play a less important part in the economy of the ant-hill. Messrs. Kirby and Spence record a fact which, isolated as it is, seems to us to overthrow altogether the hypothesis of absolute stationariness. Ants have been found, namely, to establish their nest in the interval between the double casing of a glass beehive. Now, as such beehives are artificial objects, and of very recent origin, they cannot have come in the way of the ants for any great length of time. They offered, however, a certain advantage in the uniform temperature and the shelter which they supplied. This fact must have been recognized by some prying ant, and the discovery, being communicated to its comrades, was turned to practical account. Is not this case the exact parallel of a step in the development of human civilization? And if, as we see, ants can in one case observe a phenomenon, reason on such observation, and work out their conclusions in their daily life, we can certainly see no grounds for supposing that such processes may not have occurred often. In the case of larger animals, where observation is easier, changes of habits, in accordance with new facilities or new dangers, have been distinctly recognized. There can be no necessity for us to quote the cases of alterations in the nidification of birds given by Mr. Wallace. Recent American observations show that the habits of many birds, mammalia, and even fishes, have undergone a very decided alteration in settled districts as compared with less frequented regions. All species have become more wary and circumspect in their movements, and are decidedly more nocturnal. The birds build their nests on higher trees, or in the densest thickets. Any unusual object placed in a river alarms the fishes more than a similar object would have done some years ago, and more than it does now in solitary parts of the country. A new danger is recognized, and precautions are taken accordingly.
On carefully examining the habits of ants, we find that there exist among closely-allied species, and even in different colonies of one and the same species, gradations which, to our mind, supply powerful evidence that such habits cannot have been primordial. The slave making propensity, and the reliance placed upon slaves, occur in several species, but not to the same degree. Polyergus rufescens, for instance, is absolutely dependent upon its slaves, and would, without them, perish from sheer incompetence to manage its own affairs further than by conducting slave-hunts. It is a military aristocracy, which can fight, but will rather die than work. Formica sanguinea, on the other hand, has much fewer slaves, and restricts them to a much narrower sphere of duties, being itself capable of working as well as of fighting. It is curious that the raids of slave-holding ants are confined to worker-pupae of the species which they subjugate. No instance has reached us of ants carrying off male and female pupae with a view to raising a stock of slaves in their own city, without the necessity of obtaining them by war. Surely, the most rational way of accounting for this slave-making propensity is to suppose that, as in the human race, it is a gradual outcome of war. Ants, in the wars which they are known to wage against different species, as well as against their own, would take prisoners—an undeniable fact—with the original intention of killing and devouring them. Some few of these victims, escaping immediate slaughter, might, if of a docile and submissive disposition, be found useful, and might hence be allowed to live in servitude. Prisoners of fiercer and more indomitable species, if taken at all, are no doubt killed. The query here naturally arises: "What happens in the not infrequent wars between two cities of the same species? Are the prisoners slaughtered, or are they incorporated with the victorious nation?"
No less variation may be traced in the habits of the cattle-keeping ants. Of the honey-secreting Aphides, and Cocci that serve them as milch-kine, some have large herds, some small ones, while others have none at all, and if they encounter an Aphis straightway kill and eat it. Is it not more probable that the ants first sought Aphides, like other insects, for this very purpose, but gradually discovered a way to turn them to better account, than that a flock of Aphides was, by some wonderful coincidence or interposition, placed within the reach of the first ant-hill?
It would, therefore, in our opinion, be exceedingly imprudent to declare that ant-civilization has not advanced, may not now be advancing, and may be destined to take yet further steps in the future, especially if large and fruitful portions of the globe are long allowed to remain in an uncultivated or semi-cultivated state. But such advances must necessarily be slow, as in all cases where there are no means of recording the experience of one generation for the benefit of the succeeding, and where what among mankind would be known as oral intercourse is limited by shortness of life. What direction these future advances may take, it is as difficult to indicate as to foretell the discoveries and inventions to be made by man during the next century. But we may safely say that they will not consist in the introduction of tools or weapons or machinery. Were man, in proportion to his size, about twenty times as strong as he is at present—were he provided by Nature with a pair of forceps, playing laterally, and capable of being used for felling trees, for excavating the ground, or for cutting off the heads of his enemies—he would scarcely have been a tool-inventing and tool-using animal. A being which, like the Sauba ants of Brazil, can construct a tunnel underneath the bed of a river as wide as the Thames at London Bridge, is in no need of shovels, pickaxes, or barrows.
That ants, in tropical climates, occasion much loss and annoyance to man is indisputable; yet the annihilation of all kinds of ants, were such a measure practicable, would scarcely be prudent. Here, as elsewhere, the rule holds good that small carnivora are to be cherished, and small herbivora and omnivora destroyed. The carnivorous ants, such as the Ecitons, are invaluable, from the myriads of cockroaches, scorpions, centipedes, venomous spiders, grasshoppers, and even rats and mice, that they destroy. They keep down serpents, also, by devouring their eggs. The plant-eaters, on the contrary, and especially the leaf-cutters, are an unalloyed evil, and their destruction ought to be attempted in a much more systematic way than what takes place at present. Nor can the "cattle-keeping" ants be tolerated. Even though they may not, in their own persons, attack the fruits and the leaves of useful trees, they compass injury to the latter by cherishing and defending swarms of such pernicious vermin as the Aphides of temperate regions and the scale-insects and tree-hoppers of warmer climates. All these live by sucking the juices of plants, and over them the ants watch with a wonderful care, defending them from the attacks of birds, wasps, ichneumons, and other creatures, who would rid the poor plant of its parasites. They have even been known to build galleries of clay over the surface of a pine-apple, in order to shelter the Cocci who were destroying the fruit.
Mr. Belt found that a red passion-flower, which secretes honey from glands on its young leaves and on the sepals of its flower-buds, was carefully guarded by a certain species of ant (Pheidole), who consumed the honey, and who furiously drove off all leaf-cutters and other intruders. But, after a couple of seasons, a colony of parasitical scale-insects, which secrete honey, established themselves upon the passion-flower, to its great injury. The ants transferred their care and attention to these, and, from the guardians of the plant, became indirectly, but not the less substantially, its enemies. This is a striking proof of the untrustworthy character of our insect—or, more generally speaking, of our animal—allies. At one moment they may be defending our property from depredation, but on a slight change of circumstances their interests may cease to coincide with our own, and they may go over to our enemies. The question what animal species we ought to protect and which to destroy, and how far we ought to go in each case, becomes, on closer inspection, exceedingly complicated.
As an example of an omnivorous ant, we may take the "fire-ant" of the Amazon, of which Mr. Bates gives us a striking account: "Aveyros may be called the headquarters of the fire-ant, which might be fittingly termed the scourge of this fine river. It is found only on sandy soils, in open places, and seems to thrive more in the neighborhood of houses and weedy villages, such as Aveyros; it does not occur at all in the shades of the forest. Aveyros was deserted a few years before my visit on account of this little tormentor, and the inhabitants had only recently returned to their houses, thinking its numbers had decreased. It is a small species, of a shining reddish color, not greatly differing from the common stinging ant of our own country (Myrmica rubra), except that the pain and irritation caused by its sting are much greater. The soil of the whole village 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. The houses are overrun with them; they dispute every fragment of food with the inhabitants, and destroy clothing for the sake of the starch. All eatables are obliged to be suspended in baskets from the rafters, and the cords well soaked with copaiba-balsam, which is the only means known of preventing them from climbing. They seem to attack persons out of sheer malice. If we stood for a few moments in the street, even at a distance from their nests, we were sure to be overrun with them and severely punished, for the moment an ant touched the flesh he secured himself with his jaws, doubled in his tail, and stung with all his might. When we were seated on chairs in the evenings, in front of the house, to enjoy a chat with our neighbors, we had stools to support our feet, the legs of which, as well as those of the chairs, were well anointed with the balsam. The cords of hammocks were obliged to be smeared in the same way to prevent the ants from paying sleepers a visit." The ravages of the leaf-cutting ant (Oicodona), or Saubas of the Brazilians, have been already mentioned; but it also invades houses and carries off articles of food on a far wider scale than is ever done by rats or mice. It is capable of carrying off such a quantity as two bushels of mandioca-meal in the course of a single night! Unfortunately, the Sauba has few enemies. The number of these depredators who fall a prey to birds, spiders, wasps, tiger-beetles, etc., is too small to be of any importance. The Pseudomyrma bicolor easily repels them if they come to clip the leaves of the bull's-horn acacia on which it resides, but it is not sufficiently numerous to pursue and destroy them. The Ecitons have never been known to storm the nests of the Sauba. Thus, as we often find, for the greatest mischiefs Nature provides no remedy, and man must step into the breach, armed with carbolic acid and corrosive sublimate.—Quarterly Journal of Science.
- Journal of Linnæan Society, vol. v., p. 217.
- "Contributions to the Theory of Natural Selection," p. 227.
- "Naturalist on the River Amazon."