These differences between the fully-developed male and female present nothing very striking; but how are the singular peculiarities of structure and instinct in the “workers” to be accounted for? They are present in neither queen nor drone, yet by them they are transmitted to their offspring from one generation to another! It is true that every worker, for a time, is a potential queen, and every queen, but for the grace of Chance, might have been a worker. All depends on the food. It is remarkable, but apparently the fact, that a more generous diet, or, rather, a more stimulating diet, should so profoundly modify the organism, but, it is to be noted, this sleight-of-hand is only successfully practised on a larva during its first three days of existence. Thus the royal bee jelly stimulates the growth of the sexual organs and inhibits the development of the structures peculiar to the worker—the basket, and pollen-hairs, and so on. These structures are not made by the food; they are simply nourished or inhibited, as the case may be. Nevertheless, one cannot help being mystified by the fact that the mere difference in the quality of the food, or, rather, in the chemical constituents thereof, should cause the inhibition, or, rather, the suppression, of relatively complex structures like the corbiculum and the reduction of the number of the facets of the eye. To say that the structures inhibited, in the case of the queen, are just those which will be of no service when in her royal state, is by no means to explain the mystery. And what is true of the physical side is no less true of the psychical, for with this change of diet the behaviour of the insect, throughout its whole life, is most profoundly changed. If the pollen-basket is wanting, no less so are the instinctive actions associated with its use; if the genital organs are atrophied, so also are the instinctive acts associated therewith. This nexus between instinct and structure is not to be lost sight of.
How—and the question has often been asked—are the experiences of the infertile females, the workers, transmitted to the germ-plasm? For the workers, it has been contended, being sterile, are incapable of handing on such acquirements: this is so. These workers hold the same position in regard to the species that structures essential to well-being hold in regard to the individual. These last are not under the control of the individual, but are determined by a plus or minus quality in its germ-plasm. The worker-bees are products of the germ-plasm, committed to the care of the queens. Any strain, so to speak, of that germ-plasm which gives rise to defective workers brings about its own extinction, or elimination, sooner or later. Any strain of germ-plasm which contains, so to speak, a spark of that quality which in the individual is expressed by intelligent behaviour, will gain advantages in the struggle for existence.
The complex, the extraordinarily complex, behaviour of the worker-bees on any interpretation is still mysterious. This interpretation can be tested only by a reference to the life-history of other social-bees which have attained to a less complexity. This shows us that the sterile worker is not to be regarded as a newly-evolved type so much as an arrested stage of a more complete ancestral condition, and the fact that the worker is potentially a queen is further evidence of this.
A clue to many of the more puzzling features presented by the domestic economy of the Hive-bee may be obtained by a study of the life-history of other species of social-bees which have not attained to so high a degree of specialization. The Bumble-bees afford illustrations of the stages through which Apis mellifica, the Hive-bee, must have passed.
In the stone Bumble-bee (Bombus lapidarius), a queen, who has passed the winter in blissful sleep, will lay the foundation for a new colony on some bright May morning by collecting a small quantity of moss. This done, she starts forth to gather pollen, with which, under cover of the moss, she forms a waxen cell, mixing the newly-gathered pollen with the wax so mysteriously formed within her body, as in the case of Hive-bees of the worker type. Slowly and laboriously this waxen cradle grows. Fashioned like a globe, its inner surface is lined with pollen soaked in honey, and with the last pellet of this a number of eggs are laid arid the nursery is sealed up. By the time these labours are completed the queen is worn out; she therefore rests awhile, clinging to the outer wall of this cunningly-wrought cradle. After a few days’ rest she adds another and commonly yet a third cell to the first, joining each to the other with wax. But before the third cradle is finished the eggs in the first have hatched. The youngsters will have consumed the layer of honey-soaked pollen placed there for this purpose. They therefore require feeding, and thus the labours of this very industrious queen are still further increased. Divining the needs of her imprisoned first-born, she bites a small hole through the nursery wall and pours in a quantity of honey for their sustenance. In due time they are “full-fed,” and each spins for itself a silken vestment wherein to undergo its transformation into a worker-bee. The careful mother, during this period of transition, now scrapes away an opening through which the young bees may creep when they awake. This event takes place in the course of a few days, when her work is materially lightened, for these newly-hatched workers at once take over the duties of building nurseries and feeding the further batches of young which, for a time, follow one another in quick succession. The queen, indeed, has now nothing else to do but to lay eggs in the nurseries as they are ready. So far all the children born to her are daughters. The earliest-born, it is to be noted, were “workers”; those which follow and are tended by the workers are also females, and supplement their mother’s labours by producing fertile eggs, though they have never even seen the male of their own species. Thus, if the queen-mother die her virgin daughters carry on the colony. But it sometimes happens that she may have left no descendants capable, for the time, of laying fertile eggs. In this case, if there be larvæ still in the nursery, the workers feed them assiduously as if in the hope that some may prove fertile. But if there be no infants to be fed they apparently abandon work, become despondent, and spend the greater part of their time sitting at home by the empty cradles, till at last death comes to their rescue and the colony is extinct.
Much that baffles one in the history of the Hive-bee becomes clear in the light of the facts revealed by the life-story of the Bumble-bee. In the first place it will be remembered her first eggs produced only workers, which appeared at a time when her energies were severely strained, and their food allowance was no more than barely sufficient to sustain life. The females which appeared later produced fertile eggs, having been more abundantly fed by their infertile elder sisters. The number of fertile females which appear at this stage of the colony seems again to be regulated by the abundance of food, which varies in amount with fine, or cold, weather. Even among the worker broods fertile females may appear. They owe their fertility apparently to good luck, which afforded them the opportunity of securing more food than their sisters. The birth of young from females about whose virginity there can be no question is certainly remarkable, but it would seem that this parthenogenetic state is one of limited endurance, for towards the end of summer males appear, and these mating with some of the later-born females, lead again to the appearance of a queen, who, being fertilized, alone survives the winter to carry on the race with the succeeding summer.
Thus, then, the mysterious existence of the workers among the Hive-bees, displaying structural peculiarities and instincts so different from those of the queen-mother, is explained. For the queen, in this case, is evidently the product of a more intensified, more perfected, social system, relieved, from the first, of the labours of building and the care of her offspring, duties which the queen Bumble-bee has at first to perform for herself, because all her children die at the end of the summer. Among Hive-bees fertile workers also occasionally occur; they are probably bees which in their larval state received a more than usually abundant supply of food, or food approximating to the “bee jelly” which produces young queens. The difference, then, between the individuals of a colony of Hive-bees and one of Bumble-bees lies in the greater abundance of fertile workers and in the fact that the queen of the Hive-bees is relieved of all work from the first, and so is enabled to devote her whole energies to the duties of reproduction. She is the descendant of a race of queens which in earlier times, like the Bumble-bee queen, had to perform the duties now relegated to her daughters, who inherit not only her house-building and child-nurturing instincts, but also her potentiality for child-bearing, though this potentiality is commonly inhibited by the starvation of the reproductive activities. Selection secures survival of this state of affairs by the elimination of any tendency to lose any of these qualities on the part of the queen. The workers of the Hive-bee, in short, have not evolved their peculiarities of structure and instinct by some mysterious process of natural selection confined to the workers individually, for these, being infertile, could not transmit any of their inherent qualities or tendencies to variation in the direction of more efficient workers. On the contrary, all that they possess they inherit from the queen-mother, who transmits to her offspring the qualities and characteristics her forebears in the female line possessed in their own person.