Popular Science Monthly/Volume 3/May 1873/Instinct in Insects I
|INSTINCT IN INSECTS.|
WHAT is instinct? In what does it differ from intelligence? What explanation can be given of it in the present state of the sciences of life? All these are questions to which a positive answer is asked for the first time in our day. Philosophers and moralists do not in our time concern themselves with the relations or the differences between instinct and intelligence; for they have no means of solving problems that particularly concern biology. Without going farther back, we remember Descartes's strange notion of animal machines, adopted by Bossuet, and the whole seventeenth century; but at this time biologists in their turn attack the problem; anatomy and physiology will perhaps give us the solution sought in vain at the hands of philosophic and religious systems since the days of Aristotle and St. Thomas.
George Cuvier was the first to draw a clear distinction between instinct and intelligence, in the second edition of the "Animal Kingdom" (1829), in which he digests the works published during the course of several years, by his brother Frédéric. The latter, placed in control of the menagerie of the museum, believed that it pertained to the duties of his post to make a course of connected studies upon the animals committed to his charge: he thought, as Geoffroy Saint-Hilaire did, that such is the sole purpose of establishments of that kind. "There exists in animals," Cuvier tells us, "a faculty distinct from intelligence, which we term instinct. It makes them do acts which each individual performs without ever having seen them done, and which are repeated, from generation to generation, invariably the same. Without having learned, the animal knows; it knows from its birth, and knows so well, that it never makes a mistake, even in acts of extreme complexity, the secret of which it seems to bring with it into the world. Young ducks hatched under a hen go straight to the nearest piece of water, and boldly plunge and swim, in spite of their foster-mother's cries and distress. The squirrel lays up its winter stock of hazel-nuts and filberts; before it knows what winter is. The shepherd's dog and the pointer know how to do the duties expected of them, through a gift at birth. The bird hatched in a cage and reared a captive, if set free, will build a nest like that its parents built, on the same tree, of the same materials, in the same shape. The spider, more amazing still, weaves without any lessons the geometric network of its web; and the untaught bee builds its comb. Man too has his instinct, as animals have. By instinct the new-born child feels for and finds its mother's breast; but instinctive phenomena in man are less easy to determine, and their discovery demands careful research, because intelligence usually veils them. And yet intelligence is not wanting in animals either, only with them instinct has that predominance which intelligence takes in man."
With the exception of a few mistakes in details, Cuvier marked very accurately the line between the instinctive and the intellectual faculties, but he went no further. His character and disposition gave him but little taste for penetrating into problems of that kind. With a lofty disdain to which posterity has done justice, he left to his rival Geoffroy Saint-Hilaire the care of inquiring into the origins of vital manifestations. Cuvier affirmed simply that every species received at its beginning a certain share of intelligence, with a certain provision of instinct, so wisely proportioned as to insure the permanence of that species till the end of time, or at least till the next revolution in our globe. The intelligent race does its part with its faculties as it can; they must suffice for it. The race without intelligence, to make up for its want, brings into the world a supply of instinct which aids it to make its way. This odd theory of compensation, instinct and intellectual faculties respectively complementing each other, misled Cuvier; it agreed with the general scope of his doctrine; but it does not agree with facts. Those among animals that present the most highly-developed instinct are, unquestionably, the insects; the silky tissues of cocoons, the structures wrought by wasps, the beautiful works that are treasured in cabinets, bear witness to astonishing instinctive faculties; every thing seems to be instinct with the insects, and, if Cuvier's idea be adopted, it ought in general to be very poorly endowed as regards intelligence. We shall presently see that the truth is completely the reverse.
Besides, Cuvier had no very accurate knowledge of insects, which in his classification he degraded to a place below molluscs. We cannot address the same reproach to M. Emile Blanchard, who pursues the natural history of articulated animals, at the Jardin des Plantes. We regret keenly that in his late work on the "Transformations, Habits, and Instincts of Insects," he has not thought fit to follow the suggestions of such a title, and to dwell a little on that twofold subject of intelligence and instinct which would gain by being clearly stated. His usual studies and the direction of his labors enable M. Blanchard better than any one else to complete a blank which must be supposed one of choice only, in his work. The learned professor of the museum goes on from Cuvier's starting-point with him, and, with Flourens in his last work ("Comparative Psychology," 1865), M. Blanchard distinguishes instinct from intelligence, but he stops there. He makes no attempt whatever to measure the reciprocal influence of these two kinds of faculties in the very complex acts of insect-life; and, above all, he refrains from the study of their intelligence, full of interest as it is. "Individuals of the same species," he says, "always perform the same works without having learned any thing; instinct alone guides them." Yet, together with this instinct, as M. Blanchard himself admits, there are faculties of intellect, which offer greater difficulties of study by reason of the existence of those instinctive faculties. These very difficulties make the study more worthy of attention. How are the two classes of faculties combined? If that winged mite had nothing but the instincts that urge it, those alone would make it interesting; how is that interest increased, when in that tiny body instinct is paired with reflection that analyzes sensations, and will that determines movements! what a study might we find in these intellectual faculties used by so perfect an instinct! Does it not become indispensable to measure these faculties exactly in the case in which instinct is most developed? Suppose we were to find, contrary to Cuvier's opinion, that instinct, far from being inversely proportioned to the degree of intelligence, is just the reverse, and is greater, according as intelligence is more active.
This really is the truth, and it is important to fix this first point clearly in the study of instinct. Human inferiority in point of instinct is perhaps only apparent, since education hardly allows us to guess what we should be without it. We know from the history of more than one child found wild in the woods, especially from that of the idiot boy so well studied by Itard, what amazing instincts may be displayed by a human creature, even one absolutely without understanding, when abandoned to itself. Among all animals, insects are assuredly those in which instinct is most developed; we except neither birds with their nests, nor beavers with their dams. Among insects, those in which the highest expression of instinct is noted are bees, that build cells like the work of profound geometry; and particularly ants, acting with instincts yet higher, which seem to approach those perhaps smothered by education in man. A Genevese, Peter Huber, made these known to us. His book (1810) crowns a period of remarkable studies upon insects. Before his time, as far back as 1705, a woman, Mlle. Sybille de Merian, crossed the ocean and made a voyage to Surinam, to paint the caterpillars of the tropics; then after her come Réaumur, Da Geer, Bonnet, who watches night and day his flea, the daughter of five virgin generations, and, when it dies, writes to all Europe to disclaim any responsibility for the event. The pursuit grows a passion. Lyonnet passes his life in describing, drawing, and engraving the anatomy of the willow-caterpillar. Enthusiasm works miracles; Francis Huber, the father of the man of ants, although blind, performs the marvel of making wonderful discoveries as to things taking place in the inner darkness of beehives. Peter Huber, the son, is lost and absorbed in those societies of the ants to which he devotes his studies. While all Europe is agitated by coalitions, nothing from without reaches him.
Peter Huber observes and experiments with rare sagacity. No fact escapes him; he may remark upon it or explain it ill, but he notes it most accurately. His observations have not been contradicted; his experiments still remain patterns of care and patience. He peopled with ants, his garden, the terrace of his house, his study, his tables, which were turned into a kind of hives, and, lest this new dwelling might be unsatisfactory to the ants, and in order that they might keep at work in it, he made rain and fair weather for them; his rain-making consisting in rubbing his hand for hours at a time over a wet brush. In brief, he supplied them so richly with tempting dainties and weather-contrivances, that at last they wanted nothing better than their chance home, a bureau-drawer. Did he not even one day cherish the fantastic notion of bringing up the larvas of his ants by feeding by hand ? We cannot resist loving him for his attachment to these little, thinking beings. He meditated long over one decisive experiment nothing less than the question of setting two colonies of ants at war on the floor of his study. He hesitated and lingered to awake the casus belli which should be the signal of slaughter; he devised pretexts to adjourn the dreadful scene. "I thought over this experiment for a long time," he says, "and I constantly postponed it, because I had grown to be very fond of my captives." This recalls one of Réaumur's sayings. He observes with what celerity humble-bees rebuild their nest of moss after it has been opened to examine the inside, an intrusion which these insects allow much more patiently than honey-bees do, and he adds: "If the moss from above is thrown down pretty near to the foot of the nest, as one would naturally do without even thinking that it ought to be done to save the insects some trouble, they very soon busy themselves with putting it back in its place." To save the insects some trouble! What a love for Nature the eighteenth century had, and how differently things are done nowadays! Our entomologists study their ant-hills spade in hand; a stroke of the pick into the mysteries of that underground dwelling costs their feverish passion for inquiry nothing, and yet what a spectacle rewards such barbarity! If the spade uncovers a house of tawny ants (Formica fusea), we see under the arched top a labyrinth of low rooms, of galleries and passages, which penetrates the ground and leads to spacious chambers full of nymphæ in their cocoons, or of larvæ almost as motionless. That ant, larger than the others, which is busily coming and going, is a female; for the common ants, the workmen, have no sex; naturalists call them neuters. The female lays eggs, and some workers, surrounding her, take these, one by one, and pile them in little heaps. The worms, when hatched, would perish without the workers, being able only to lift their heads to show their want of food; a worker comes up and lets them take from between its mandibles such nourishing juices as it has brought from its quest in the fields. When the hour comes for carrying all these papooses into the sun, they carry them up and spread them out on the arched top. If the heat is too strong, or if it rains, they bring them back again at once into rooms of suitable temperature. When the time of their transformation comes, the larva has spun itself a cocoon, but is quite unable to get out of it alone. It is the duty of the workers again to extract it; they cut the silk, tear the shell, release the weak, new-grown creature, and then the old empty cocoons are stored away in a remote chamber. Thus are produced males, females, and neuters. The males and females fly off; some females will come back to lay eggs in the ant-hill; the neuters do not leave it. As soon as they have gained a little strength, they set about all those labors that instinct teaches them—the repair and keeping in order of the ant-hill, inside and without, carrying of useful materials, pursuing plant-lice, and gathering stores of all kinds. Assuredly, these instincts alone are very wonderful; but there remains still another to be spoken of, peculiarly conferred on certain species, and which is indisputably the highest of all those we know among animals.
Peter Huber discovered it on the afternoon of the 17th of June, 1804. The date is a memorable one for biology. He was walking in the environs of Geneva, between four and five o'clock in the evening, when he saw a regiment of great red ants crossing the road. They marched in good order, with a front of three or four inches, and in a column eight or ten feet long. Huber followed them, crossed a hedge with them, and found himself in a meadow. The high grass plainly hindered the march of the army, yet it did not disband; it had its object, and reached it. This was the nest of another species of ants, blackish-gray ones, whose hill rose in the grass twenty steps from the hedge. A few blackish-gray ones were scattered about the hill; as soon as these perceived the enemy, they darted upon the stranger, while others hurry into the galleries to give the alarm. The besieged ants come out in a body. The assailants dash upon them, and, after a very short but very spirited struggle, drive the black-gray ones back to the bottom of their holes. One army corps presses after them into the galleries, while other groups labor to make themselves an opening with their teeth into the lateral parts of the hill. They succeed, and the remainder of the troop makes its way into the besieged city by the breach. Peter Huber had seen battles and exterminations of ants before this; he supposed they were slaughtering each other in the depths of the caverns. What was his amazement, after three or four minutes, when he saw the assailants issue hurriedly forth again, each holding between its mandibles a larva or a nympha of the conquered tribe! The aggressors took exactly the same road again by which they had come, passed through the hedge, crossed the road, at the same place, and made their way, still loaded with their prey, toward a field of ripe grain, into which the honest citizen of Geneva, respecting another's property, refrained, with regret, from following them.
This expedition, worthy of the annals of barbarian piracy, inspired Huber with an amazement easy to understand. He examined, and discovered, to his great surprise, that some ant-hills were inhabited in common by two kinds of ants, forming two castes. He designates one of these by the name of "amazon or legionary ants; a name strongly suggesting their martial character," he says. The others he calls, very justly, "auxiliaries." The amazons do not work; their duty is fighting and carrying off the nymphæ and larvæ. They choose the hour toward sunset for their warlike raids against the industrious and peaceable tribes of the neighborhood. Whenever the weather is fine, they sally out thus, and levy their tribute of flesh. The auxiliaries, for their part, are employed in all internal duties, and in keeping up and repairing the dwelling. They alone open and close the entrance to the ant-hill, night and morning; they alone (in the species observed by P. Huber) go after provisions, for they feed the whole establishment, even the legionaries, which are idle except when on their forays; they rear with equal care the larvæ of the legionaries and those that are stolen; they alone, in fine, seem to decide upon the material interests of the community, the requisite enlargements, the need of emigration, and the place suitable for it. Peter Huber made one experiment that shows very plainly the absolute dependence of the amazons upon their associates. These fierce warriors do not understand any household work. Huber put thirty amazons into a glazed drawer, covered, with earth on the bottom, with a certain number of larvæ and of nymphæ, both of their own kind and of the auxiliary species. A little honey in a corner was provided for the support of the colony. At first, the amazons seemed to pay some attention to the larvae, carrying them about here and there, but they soon left them. They did not know how to provide themselves with food. At the end of two days some had already died of hunger close alongside the honey-drops, all were languishing, and they had not even built a chamber. "I was sorry for them," says Huber. He put an auxiliary into the drawer. This solitary one restored order, made a house in the earth, gathered the larvae into it, released several nymphæ of both kinds that were ready to leave the cocoon, and at last saved the lives of those among the amazons that still had breath.
Peter Huber refrains from any comments in describing all these wonders; he leaves each one, as he says, at liberty to draw any conclusions he pleases. This one conclusion is inevitable: We do, then, find among animals artificial societies, communities of beings strangers in race, yet living together, contributing, toward one common end, their different qualities and their individual efforts. The hive is always one family only. A mixed ant-hill is inhabited by individuals belonging to species at least as different as the horse, the ass, the zebra so different sometimes that zoologists have classed them in distinct genera (Polyergus formica). Like provinces subject to the same form of government, every ant-hill has, nevertheless, its local history, explained by external circumstances, by conditions of neighborhood and boundary. Each one has only the principle of its organization in common with the rest. The same legionaries have sometimes one species of auxiliaries and sometimes another, the black-grey or the mason ant, whichever is within their reach, sometimes both together; or there may be two kinds of legionaries, the "polyergus" and the dark-red, living in the same hill, with one or two species of auxiliaries. Some naturalists, Darwin among others, call these frankly "slave-holders," and the others "slaves." These names are unfair. We must guard against any mistake as to the very peculiar nature of the relations existing between the two castes. Each fills a special part in the community, and neither exercises control or despotism in it. If the association, at the outset, rests on violence and abduction, nothing has ever given rise to a suspicion that there is any thing else in a mixed ant-hill than a collection of individuals kept together by special instincts. These names of "slavery" and "republic," applied to such a form of life, are quite void of meaning. Any allusion to politics, to systems, or doctrines of equality, is wholly out of place here; biology alone has the right of giving a name to a social state which is its peculiar subject of study; this territory belongs to it alone.
We have selected these instances because they furnish the most striking proof both of the perfection that instinct may reach, and of the degree of intelligence of which animals are capable which are placed by their nature at an immeasurable distance from man. Peter Huber did not clearly draw the distinction, nor could he do so in his time, between that which is instinct and that which is the share of intelligence in those acts which he witnessed. It is clear that these two orders of faculties are constantly combined. It is by reason of their perfection in instinct that intelligence appears so clearly in these little beings. The construction of the ant-hill is an act of instinct; the choice and distribution of its materials partake of intelligence. A thousand traits reveal the thought which perceives, deliberates, wills, executes. We may cite the observed fact of a crowd of ants dragging with great effort a beetle's wing toward their hole. The opening is too small, the wing will not go in. The workers drop it a moment, tear down a piece of the wall, and renew their attempt. Some push it from outside, others drag it from within. Fruitless effort! The superb spoil, which will make an entire ceiling, will not pass yet; they drop it once more; the breach is widened, and the wing at last is swallowed up in the cavern, where perhaps ten partitions must be torn down to carry it to the proper place. The wing once got in, they rebuild the wall, and restore its former dimensions to the entrance. We cannot cite, in the case of monkeys watched in captivity in menageries, a single instance so clearly showing deliberation and common judgment.
The social phenomena presented by the higher animals are unfortunately very little known. We know scarcely any thing of what goes on in a habitation of beavers; we know nothing of the habits of the republican sparrow, which builds a city for its nest; the insect communities are the most perfect ones that have been studied hitherto. So soon as a society exists, there are understanding and concurrence of all at every moment to reach a definite object. No zoologist now doubts that insects of the same species may communicate with each other, under certain circumstances, by a language of which the methods elude us. Blanchard says of the ant: "It has its ideas, and communicates them;" but a singular detail of the history of the sacred scarabee shows this still more clearly. The female, as we know, wraps up her newly-laid egg in a ball of manure, the nourishment for the coming grub. The point now is to transport the ball into a suitable place, where it may be buried. The insect rolls along, with its hind-claws, or, if necessary, hoists with its head, this little world, in which the Egyptians found an emblem for their myths. Sometimes the journey is pretty long; the ball, lifted to the ridge of a mole-hill, rolls down the other side, and so much is gained. But, if a rut or a crevice is encountered, the precious globe drops to the bottom, and would be hopelessly lost if the scarabee had only its own strength to depend on for mounting that steep wall. It struggles in vain, and begins again twenty times over; at last it seems to desert its load, and flies off. Wait and watch; after a little while you will see the insect coming back, but not alone now. It is followed by two, three, four, five companions, which all drop down into the place pointed out, combine their efforts, drag out the ball, and set it on its path again. What did the scarabee say to its comrades? how did it make itself understood? how did it bring them back with it? It is not possible to make any positive answer to these questions; what is beyond dispute is, that there was in this case a concert of intelligences knowing how to understand each other and to come together. Nothing more is needed for the assertion that the insect judges, wills, and perhaps speaks, a language of which we know as yet neither the signs nor the organs.
Cuvier, then, was in error when he announced that instinct in animals is in an inverse ratio to their intelligence. The contrary seems rather to be true, and it is at least probable that in those intelligences of insects which feel, will, understand, deliberate, there are, on a finer scale, differences similar to those we remark in the higher animals. The faculty is common to all, but with shades as marked among the wild beasts of menageries as among our domestic animals. One is cross, and another jealous; this one is good-tempered, that other quarrelsome, faithful to the house, or a vagabond in the streets—all are more or less intelligent. In the lower animals these differences have not been as closely observed; in the first place, they are probably less distinctly marked, and in any case they are much more difficult to observe for reasons of all kinds. The small size of the being, its life wholly alien to our own, the predominance of instinct, are all so many impediments; but, on the other hand, the acts we see them perform under our very eyes, the admitted existence of faculties that may be compared with our own, and those of a relatively high order, allow of very little doubt that not only do insects possess a remarkably-developed intelligence, but that this intelligence presents, in consequence of its very development, individual variations, just as in the higher animals.
This is already a great advance upon Descartes, whose strange theory no one at this day, that we are aware of, undertakes to defend; but this is not all—a new step has been taken in these later times. We are beginning, with our better knowledge, to ask whether those intellectual and instinctive faculties, arranged by Cuvier in two parallel series, may not have some common bond, so that one would flow from the other, and instinct, after all, be definitely a product of intelligence. The question has its importance. Instinct would then no longer be one of those essential properties of living beings which absolutely elude our comprehension, such as thought in the brain, contraction in the muscles, the electricity of the eel, or the gleam of the glow-worm; it would be accessible, like all dependent phenomena, to our processes of experiment and investigation.
Darwin is entitled to the credit of having taken the question into this entirely new region. This bold attempt to found the scientific study of instinct is found rather indefinitely in the "Origin of Species." Darwin does not enter on the problem with deliberate purpose as a physiologist. He continues to be what he is in the whole work, the zoologist, exclusively occupied with his great theory: he foresees and meets objections; he has particularly anticipated those that might be brought against him in the name of instinct; and he gives, in a few pages, a more complete study of instinct than any philosopher had made before him, and the first study ever made by aid of experiment. He ignores instinct as an essential property, and treats it as a function—that is, he explains it. Instinct, as he holds, is nothing but a result from the intellectual faculties, properly so called, modified in a particular way under the twofold power of habit and inherited influence.
Inherited tendency, like intelligence, is one of those properties peculiar to living beings of which we can prove the existence, while its principle completely and absolutely baffles investigation. When we attempt to pierce the mystery by which the plant that springs from theseed, the bird that grows from the yelk, will be more like the plant or the bird it proceeds from than like any other, we confront the impenetrable unknown. Hereditary tendency does not merely carry down from one generation to another all the imaginable modifications of form, size, coloring; it extends to the cerebral faculties, transmitted doubtless by the help of some physical peculiarity of the organ of intelligence. This is what is called the spirit of race, which decides that one people shall be born brave and crafty, like the Greeks of Homer; industrious, like the Chinese; traders, like the Jews; or hunters, like the red-skin. This is, if we choose to term it so, a kind of instinct that education sometimes allows us to control, but never eradicates. As the wolf, fattened in the kennel, ends by going back to his wretched life of the woods, the child of a savage reared in the midst of civilization preserves in his mind, as upon his features, the deep, hereditary stamp of his origin. Habit, almost as much as hereditary tendency, is another mysterious faculty which we recognize without being able to explain it. Some act, most difficult in appearance, which required on the part of our brain a considerable effort of will and all our mental activity, at last surprises us by almost performing itself. We might say that attention and reflection have gone down into our limbs, which perform the most delicate tasks, and protect themselves against attacks from without, while the mind, occupied with something else, is pursuing a different object.—Revue des Deux Mondes.