Animal Behaviour

by C. Lloyd Morgan

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.