Animal Behaviour

by C. Lloyd Morgan

III.—Social Communities of Bees and Ants

Apart from human societies the most noteworthy social communities of animals are found among insects, especially in ants, bees, wasps, and termites. It is true that in the mammalia we find such communities as the troop of apes, the herd of cattle, the pack of wolves, the school of porpoises, the so-called “rookeries” of seals, and the colonies of “prairie dogs” and of beavers; and that among birds there are analogous communities. Undoubtedly the temporary or permanent association of many individuals is in such cases an advantage to the race, and confers mutual benefits on the associates. But in none of these cases is division of labour carried to such a high degree as among the social insects. And it is through such division of labour that the social community reaches its highest expression.

It is a somewhat remarkable fact that in man, where we find the social division of labour brought to a high pitch of perfection, and carried out with great nicety of accommodation to those circumstances which civilization has rendered extremely complicated, there is no organic differentiation of structure among the co-operating individuals; whereas, so low down in the scale of life as the colonial polype, Hydractinia, which is often found growing on the shells occupied by hermit crabs, there are at least three kinds of differentiated individuals: nutritive polypes with mouth and tentacles; mouthless sensitive members; and others whose sole office is reproduction. But these differentiated individuals in the colonial zoophytes are connected at their bases by a common flesh; and the division of labour is a product of organic evolution, and is probably not in any degree determined or guided by consciousness. We may say, then, that the division of labour in the zoophyte is wholly physical, whereas in man it is chiefly conscious or psychical; as is also the bond of union between the several members of the colony. Intermediate between these extremes stand the social insects. In them there is no physical bond of union, for each individual is distinct and separate; the social linkage is in some degree conscious under the conditions of their nurture; and the division of labour is partly conscious, though probably in large degree based on instinctive foundations, and partly the outcome of an organic differentiation of structure seen in the reproductive members and in the sterile workers, as exemplified in the common wood ant (Fig. 24). In some cases the workers themselves may be divided into different castes.

Fig. 24.—Wood ant. 1, Queen; 2, male; 3, worker (from Shipley).

So much has been written—and well written—on the social life of insect communities, that it will here suffice to indicate some of the problems which arise when we endeavour to interpret the modes of behaviour which have been carefully observed. In the honey-bee we have the well-known differentiation of structure into drones or effective males, queens or egg-laying females, and workers or ineffective females, in which the development of the reproductive organs is arrested or modified. Distinct modes of behaviour are correlated with these structural differences. When a swarm of bees leaves a hive it generally consists of the old queen-mother and a certain number of the workers which are her offspring. When they have found new quarters, or have been safely housed under domestication, the workers busy themselves in making the cells in which the queen may lay her eggs, and in which food may be stored. In doing this the bees act in concert, and though the mathematical accuracy of the form and size of the cells has been much exaggerated, the comb which results is a very beautiful and well-adapted product of mutual co-operation in joint labour. And though intelligence may, under special circumstances, modify the method of procedure there can be little doubt that comb-building is primarily due to inherited instinct. The cells are not, however, all of the same size, those for the drones being somewhat larger than the cells in which the workers are reared, while much larger and differently shaped cells are prepared for the future queens. If instinctive therefore—as it seems to be in the main—the behaviour runs into different lines, the immediate causes of which, internal or external, we are not able accurately to assign.

The reproductive behaviour of egg-laying in the queen-mother is also instinctive. It is believed that the drones are developed from eggs from which the queen bee withholds the fertilizing fluid, which she retains for months or years after the nuptial flight, stored in a special receptacle. And the size and shape of the drone-cell may supply the stimulus through which her behaviour in this respect is determined. But she lays similarly fertilized eggs in both the worker-cells and the queen-cells; and in these two cases the stimulating conditions must be different.

When the eggs have been laid, and the grubs hatched, the worker bees assume new duties—the feeding and tending of the young. They eat honey and pollen, which is partially digested, and supplied as pap to the grubs in such quantities that they seem bathed in it; but after a short time a mixture of honey pollen and water is substituted for this pap. It is said that the drone larvæ are fed with pap for a longer period than the workers; and the queen larva undoubtedly receives far more of this pap—or, perhaps, of a still richer nutritive product, sometimes spoken of as royal jelly—and, indeed, is supplied therewith throughout larval life. It is generally believed that this high feeding is the cause of queen-development, and that should the queen larvæ die ordinary worker larvæ are fed up, and produce queens nowise dissimilar to those developed in the royal cells. It is clear, if this be so, that the behaviour of the nurses decides the difference between the future queens and working bees—that is to say, the fertile and the sterile females. In any case, the feeding of the young by members of the same community is a fact to be specially noted. It is commonly said that the family is the germ from which the social community springs; and it may be added that food-collection or food-administration in some form makes the difference between the family that coheres and the family that scatters.

When the larvæ have been fed, each after its kind, the workers seal up the cells with lids of pollen and wax; the larvæ spin cocoons, pass into the pupa stage, and then change to perfect bees, which bite a way through the lid and take their place in the hive. These young bees now become the nurses, while the older bees go abroad to fetch honey and pollen to be stored away in some of the cells. But when a queen emerges, her first act is to go round to the other royal cells, tear them open, and sting to death the helpless occupants. Meanwhile the old queen may have led off the surplus population in a swarm, and the new queen reigns in her stead. Idle drones have also been emerging from their cells; and when the young queen starts forth on her nuptial flight she is followed by the drones, mates with one of them, and returns a potential mother of thousands. So long as there is abundance of food the useless drones are tolerated; but when there is scarcity they are ejected, and drone eggs, larvæ, and pupæ are said to be destroyed.

In the works of Huber and others, further marvels of hive-life, some well-authenticated, others more or less doubtful, are duly set forth. But enough has here been said to show that a social community of bees presents problems of animal behaviour which are sufficiently difficult of explanation. How far is the behaviour instinctive? How far is it due to experience individually acquired? Are we constrained to admit a rational factor? If so, is it, like human reason, the result of generalization from experience of the relationships of phenomena? Or are there features of insect psychology which differ from any of which we have firsthand knowledge? These questions are more easily put than answered. As in the case of bird-migration, so too in that of the social life of bees, there is much that honesty forces us to confess our inability satisfactorily to explain.

So, too, is it in the social life of ants. Among these insects the males and perfect females bear wings, though these appendages may be subsequently shed. In some kinds, however, there are also wingless males or females capable of exercising the reproductive function. The workers are wingless, and are often of two or three kinds, differing in form and appearance, and in some cases playing different parts in the social economy. There is also, in some cases, a separate class of large-headed soldier ants; so that differentiation of structure among the sterile females is carried further in ants than in bees. Their nests generally consist of an elaborate system of chambers and passages, either built with pine-needles, as in our common wood ant, or hollowed out in the earth or in wood, or sometimes built with a paper-like material, or formed of rolled leaves. It is said that a common ant in Eastern Asia (Œcophylla smaragdina) “forms shelters on the leaves of trees, by curling the edges of leaves and joining them together.... The perfect ant has no material with which to fasten together the edges it curls; its larva, however, possesses glands that secrete a supply of material for it to form a cocoon with, and the ants utilize the larvæ to effect their purpose.”[91] This has recently been confirmed by Mr. E. G. Green, Government entomologist, at the Botanic Gardens at Peradeniya, Ceylon. “He has seen ants actually holding larvæ in their mouths and utilizing them as spinning machines. To find out what would be done, some leaves were purposely separated by Mr. Green. The edges of the leaves were quickly drawn together by the ants, and, about an hour later, small white grubs were seen being passed backwards and forwards across the gaps made in the walls of the shelter. A continuous thread of silk proceeded from the mouth of the larva, and was used to repair the damage.”[92] This is a remarkable act of apparently intelligent behaviour. But when we remember how much of the time of ants is occupied in carrying about their larvæ, it is hardly an act of which it can be affirmed that it could not arise as the result of chance experience.

In some cases two different genera are found in the same nest, with separate chambers and passages, as in the case of the robber-ant (Solenopsis) and the slave-ant (Formica fusca). The orifices by which the former enter are too small to allow of the entrance of the latter, “hence the robber obtains an easy living at the expense of the larger species,” for “they make incursions into the nurseries, and carry off the larvæ as food.”

In a few cases the foundation of a new colony has been carefully watched. Blockmann was successful in observing the formation of new nests by Componotus ligniperdus at Heidelberg. “He found under stones, in the spring, many examples of females, either solitary or accompanied only by a few eggs, larvæ, or pupæ. Further, he was successful in getting isolated females to commence nesting in confinement, and observed that the ant that afterwards becomes the queen, at first carries out by herself all the duties of the nest. Beginning by making a small burrow, she lays some eggs, and when these hatch, feeds and tends the larvæ and pupæ: the first specimens of these latter that become perfect insects are workers of all sizes, and at once undertake the duties of tending the young and feeding the mother, who, being thus freed from the duties of nursing and of providing food while she is herself tended and fed, becomes a true queen-ant. Thus it seems established that, in the case of this species, the division of labour found in the complex community does not at first exist, but is correlative with increasing numbers of the society. Further observations as to the growth of one of these nascent communities, and the times and conditions under which the various forms of individuals composing a complete society first appear, would be of considerable interest.”[93]

The queen does not, as in the case of the bee, deposit her eggs in separate cells where they are tended by nurses. The eggs, which are laid in the chambers of the nest, are subjected to much licking by the nurses; the larvæ are, moreover, moved about from place to place, so as to be subjected to the requisite conditions of moisture and temperature. They are carefully cleaned, and after they have passed into the pupa stage the emerging insects are stripped of a delicate investing skin. And not only do the ants assiduously feed their young; those who have gone forth and drunk their fill of sweet juices feed those who have remained behind. Forel took some specimens of Componotus ligniperdus, “and shut them up without food for several days, and thereafter supplied some of them with honey, stained with Prussian blue; being very hungry, they fed so greedily on this that in a few hours their hind bodies were distended to three times their previous size. He then took one of these gorged individuals, and placed it among those that had not been fed. The replete ant was at once explored by touches of the other ants and surrounded, and food was begged from it. It responded to the demands by feeding a small specimen from its mouth, and when this little one had received a good supply, it in turn communicated some thereof to other specimens; while the original well-fed one also supplied others, and thus the food was speedily distributed. This habit of receiving and giving food is of the greatest importance in the life-history of ants.”[94] It affords the basis or starting-point of the keeping of aphides, the making of slaves, the curious development of honey-pot ants, and in some cases the association with ants of other insects.

Fig. 25.—Beetle soliciting food from Ant (after Wasmann).

Some of these insects, of which there are many species belonging to several orders, are parasitic; others appear to be hostile, and yet are able to maintain themselves in the nest; others simply live side by side with the ants, which seem to be neither hostile nor friendly to them. In some of these cases the biological purpose of the association is unknown, while in others the ant serves as a model which the associated insect mimics. Thus in the nest of an Indian ant (Sima rufa-nigra) occur a small wasp and a spider which, to some extent in form and more markedly in coloration, mimic their hosts. “Wherever you find this species in any numbers,” says Mr. Rothney,[95] “if you watch a few moments, you will see a mimicking spider, Salticus, running about among the ants, which it very closely resembles in appearance, much more so in life than in set specimens placed side by side; I have seen numbers on the most friendly footing with the ants, though I have never seen them enter their burrows.... They are, I should say, the only friends the ant has, with the exception of a sand-wasp, a new species of Rhinopsis since described by Mr. Cameron, which also very closely mimics the ant, and which, on first observing among the workers, I took to be the male.” But there are some beetles which are not only tolerated, but fed by the ants with which they live. In the case of the genera Atemeles and Lomechusa, which are always found in or near ants’ nests, the good offices are reciprocal, for the beetles “have patches of yellow hairs, and these secrete some substance with a flavour agreeable to the ants, which lick the beetles from time to time. On the other hand, the ants feed the beetles; this they do by regurgitating food, at the request of the beetle, on to their lower lip, from which it is then taken by the beetle. The beetles in many of their movements exactly resemble the ants, and their mode of requesting food, by stroking the ants in certain ways, is quite ant-like. So reciprocal is the friendship, that if an ant is in want of food the beetle will in its turn disgorge for the benefit of its host. The young of the beetles are reared in the nests by the ants, who attend to them as carefully as they do to their own young. The beetles are, however, fond of the ants’ larvæ as food, and, indeed, eat them to a very large extent, even when their own young are receiving food from the ants. Wasmann (to whom we are indebted for most of our knowledge on this subject) seems to be of opinion that the ants scarcely distinguish between the beetle larvæ and their own young; one unfortunate result for the beetle follows from this, viz. that in the pupal state the treatment that is suitable for the ant larvæ does not agree with the beetle larvæ. The ants are in the habit of digging up their own kind, and lifting them out and cleaning them during their metamorphosis: they do this also with the beetle larvæ, with fatal results; so that only those that have the good fortune to be forgotten by the ants complete their development.”[96]

Aphides, or plant-lice, yield to the solicitations of ants, which stroke them with their antennæ, by emitting a drop of sweet and viscid secretion, and it appears that the caress of the ant is the natural stimulus for the emission of the drop. Not only, however, do the ants go forth in search of aphides in their natural haunts, they bring them to the neighbourhood of the nest, and may even impound them by building a wall of earth round and over them. Huber stated that ants collected the eggs of the aphides and tended them in their nests, and the accuracy of the observation has been shown by Lord Avebury and others. “The aphid eggs are laid early in October, on the food plant of the insect. They are of no direct use to the ants, yet they are not left where they are laid, where they would be exposed to the severity of the weather and to innumerable dangers, but brought into the nests by the ants, and tended by them with the utmost care through the long winter months until the following March, when the young ones are brought out and again placed on the young shoots of the daisy.”[97] Dr. McCook noticed that ants, returning from the trees on which aphides abounded, fed others near the nests, and he regarded this as a case of division of labour, the foragers obtaining food for the nurses which remained in or near the nest.

A further division of labour, carried to lengths which seem almost absurd, is found in the honey-pot ant of the United States and Mexico. The juice on which these ants feed is obtained from an oak-gall. Foragers go forth at night and return distended with the sweet fluid, and, having fed the ordinary workers in the nest, apparently discharge the balance of their store into living honey-pots, which remain in the nest and preserve the food till it may be required by the members of the community. Their abdomens are enormously distended, they never leave the nest, and they seem to form a distinct caste, whose function it is to passively accumulate stores of reserve food for the community. Curiously enough the same peculiar social arrangement is found in different genera living as far apart as Mexico, Australia, and South Africa.

Fig. 26.—-Honey-pot Ant.

There is no doubt that in some cases the division of labour is not restricted to the individuals of the same species, but that other species are introduced into the nest to perform certain functions—thus giving rise to the so-called slavery among ants. This is carried to an extreme in the European species Formica rufescens, the males and queens of which do no work, while the sole function of the workers is to capture slaves of the smaller species Formica fusca. In association with this specialized mode of instinctive behaviour, “even their bodily structure has undergone a change; their mandibles have lost their teeth, and have become mere nippers, deadly weapons indeed, but useless except in war. They have lost the greater part of their instincts: their art—that is, the power of building; their domestic habits—for they take no care of their own young, all this being done by the slaves; their industry—they take no part in providing the daily supplies; if the colony changes the situation of its nest, the masters are all carried by the slaves to the new one; nay, they have even lost the habit of feeding.... I have had a nest of this species under observation for a long time, but never saw one of the masters feeding. I have kept isolated specimens for weeks, by giving them a slave for an hour or two a day to clean and feed them, and under these circumstances they remained in perfect health, while, but for the slaves, they would have perished in two or three days.”[98]

In this matter, we have in different species successive stages in the development of the instinctive behaviour which is thus carried so far in Formica rufescens. Our English ants, of the species Formica sanguinea, have fewer slaves and are less dependent on them; they can feed and forage for themselves, and during migration carry their slaves—which are of the same species as in the other case—instead of being carried by them. In the nests of the common wood ant or horse ant (Formica rufa) there are occasionally a few slaves. Lord Avebury thinks it likely that they are developed from larvæ or pupæ, originally taken for food, which have by chance come to maturity in the nest of their captors.

But one more incident in the social life of ants can here be noticed—though many others could be given did space permit. The leaf-cutting ants of America form paths from their nests to suitable trees, from which to obtain the small coin-like leaf fragments, which they carry in the mandibles, and hence have gained the name of umbrella or parasol ants. These paths are sometimes underground; and Mr. McCook measured one which ran at a depth of some 18 inches beneath the surface for 448 feet, and was then continued for another 185 feet to the tree which the ants were stripping. The whole path was in an almost perfect straight line from nest to tree. The leaf fragments are stored in large quantities in the nest, and it was long a matter of uncertainty for what purpose they were collected. The problem was solved by Alfred Möller, who found that the leaves, which are subdivided and masticated by a special set of workers within the nest, form the appropriate material in which the threads of a fungus ramify and flourish. This fungus is tended by the ants with great care, and is made to produce a specially modified form of growth, not found under other circumstances, in the form of white aggregations, termed by Möller “Kohlrabi clumps.” These form the principal food of the ants; and the spongy mass of earth and leaves is called the fungus garden. “If a nest be broken into and the fungus garden scattered, the ants collect it as quickly as possible, especially the younger parts, taking as much trouble over it as over the larvæ. They also cover it up again as soon as possible to protect it from the light.”[99]

Again, it may be asked with regard to the social life of ants as with respect to that of bees—How far is their complex behaviour instinctive? How far is it due to imitation? What part does intelligence play, and under what conditions of acquisition? Is reason, in the restricted sense of the word, a factor in the development of the behaviour? I cannot answer these questions, and am of opinion that much detailed observation is yet needed before we can do much more than speculate in the matter. Much indeed has been done, but yet more remains for future investigation.

The conditions under which much of the behaviour is carried out seem to indicate strong instinctive tendencies which give an hereditary trend to the direction which the social behaviour takes. Dr. Bethe,[100] indeed, goes so far as to regard the behaviour as almost entirely instinctive, affording little evidence of that modifiability of reactions which indicates intelligent guidance. He shows as the result of careful experiment that the behaviour of ants to friends and enemies are direct reactions to smell. Enemies washed with the excretions of members of the nest are treated as friends, notwithstanding their different colour, size, and general appearance. By scent, too, they follow the lead of others and retrace their way to the nest; this, he says, is not the result of a mental process, but is the reaction of a complicated reflex mechanism. As the outcome of careful observation, Dr. Bethe’s conclusions are of great value and interest. But he seems to go too far in denying to ants any power of intelligent accommodation to circumstances. If we admit intelligence, then the fact that the insects come forth in the midst of a community in full social activity would tend to the imitative or intelligent acquisition of like modes of procedure. It is difficult to distinguish the share taken by these two factors which may well co-operate. And if natural selection is exercising its influence through the elimination of those which do not fall into line in social behaviour, there would be ample opportunity for the survival of coincident variations.[101] If one may be allowed to speculate, it seems probable that the interaction of instinct and intelligence will be found with fuller knowledge to suffice for the explanation of the facts, without calling in the known but here improbable factor of rationality or any factors unknown elsewhere in psychology.

Some interesting observations of Lord Avebury’s are sometimes quoted as evidence that ants are lacking in intelligence, but (if we accept the distinction already drawn[102]) they seem rather to show the lack of reason. “I placed food,” he says,[103] “in a porcelain cup, on a slip of glass surrounded by water, but accessible to the ants by a bridge, consisting of a strip of paper two-thirds of an inch long and one-third wide. Having then put an ant (Formica nigra) from one of my nests to this food, she began carrying it off, and by degrees a number of friends came to help her. When about twenty-five ants were so engaged, I moved the little paper bridge slightly, so as to leave a chasm just so wide that the ants could not reach across. They came to the edge and tried hard to get over, but it did not occur to them to push the paper bridge, though the distance was only about one-third of an inch, and they might easily have done so. After trying for about a quarter of an hour they gave up the attempt and returned home. This I repeated several times. Then, thinking that paper was a substance to which they were not accustomed, I tried the same with a bit of straw one inch long and one-eighth of an inch wide. The result was the same. Again, I placed particles of food close to and directly over the nest, but connected with it only by a passage several feet in length. Under these circumstances it would be obviously a saving of time and labour to drop the food on to the nest, or at any rate to spring down with it, so as to save one journey. But though I have frequently tried the experiment, my ants never adopted either of these courses. I arranged matters so that the glass on which the food was placed was only raised one-third of an inch above the nest. The ants tried to reach down, and the distance was so small that occasionally, if another ant passed underneath just as one was reaching down, the upper one could step on to its back, and so descend; but this only happened accidentally, and they did not think of throwing the particles down, nor, which surprised me very much, would they jump down themselves. I then placed a heap of mould close to the glass, but just so far that they could not reach across. It would have been quite easy for any ant, by moving a particle of earth for a quarter of an inch, to have made a bridge by which the food might have been reached, but this simple expedient did not occur to them.”

Now, when we remember that the method of intelligence is to profit by chance experience, while the method of reason is, with foresight and intention, to adapt means to ends, we shall see that to move a straw even a quarter of an inch, or to make a bridge with particles of mould, would require rational and not merely intelligent powers. Chance experience would not supply the necessary data to be utilized by intelligence when repetition had established an association in the conscious situation. Granting that the ants were intelligent but not rational, they could not be expected to overcome the difficulties, simple as they seem to us, which Lord Avebury placed in their path. Had they been overcome the fact would be more difficult to explain than the use of a stone tool by the sand wasp, since this could more readily be hit upon by chance experience. And what these valuable experiments, of which kind more are needed, seem to show is, that the ant, probably the most intelligent of all insects, has no claim to be regarded as a rational being.