After obtaining the dwelling, the Carpenter-bee behaves like the Osmia who is in possession of a reed. Provisions are collected, the egg is laid and the chamber is walled in front with a saw-dust partition. The work is pursued in this way until the two or three passages composing the house are completely stocked. Heaping up provisions and erecting partitions are an invariable feature of the Xylocopa's programme; no circumstance can release the mother from the duty of providing for the future of her family, in the matter both of ready-prepared food and of separate compartments for the rearing of each larva. It is only in the boring of the galleries, the most laborious part of the work, that economy can occasionally be exercised by a piece of luck. Well, is the powerful Carpenter, all unheeding of fatigue, able to take advantage of such fortunate occasions? Does she know how to make use of houses which she has not tunnelled herself? Why, yes: a free lodging suits her just as much as it does the various Mason-bees. She knows as well as they the economic advantages of an old nest that is still in good condition: she settles down, as far as possible, in her predecessors' galleries, after freshening up the sides with a superficial scraping. And she does better still. She readily accepts lodgings which have never known a drill, no matter whose. The stout reeds used in the trellis-work that supports the vines are valuable discoveries, providing as they do sumptuous galleries free of cost. No preliminary work or next to none is required with these. Indeed, the insect does not even trouble to make a side-opening, which would enable it to occupy the cavity contained within two nodes; it prefers the opening at the end cut by man's pruning-knife. If the next partition be too near to give a chamber of sufficient length, the Xylocopa destroys it, which is easy work, not to be compared with the labour of cutting an entrance through the side. In this way, a spacious gallery, following on the short vestibule made by the pruning-knife, is obtained with the least possible expenditure of energy.
Guided by what was happening on the trellises, I offered the black Bee the hospitality of my reed-hives. From the very beginning, the insect gladly welcomed my advances; each spring, I see it inspect my rows of cylinders, pick out the best ones and instal itself there. Its work, reduced to a minimum by my intervention, is limited to the partitions, the materials for which are obtained by scraping the inner sides of the reed.
As first-rate joiners, next to the Carpenter-bees come the Lithurgi, of whom my district possesses two species: L. cornutus, FAB., and L. chrysurus, BOY. By what aberration of nomenclature was the name of Lithurgus, a worker in stone, given to insects which work solely in wood? I have caught the first, the stronger of the two, digging galleries in a large block of oak that served as an arch for a stable-door; I have always found the second, who is more widely distributed, settling in dead wood—mulberry, cherry, almond, poplar—that was still standing. Her work is exactly the same as the Xylocopa's, on a smaller scale. A single entrance-hole gives access to three or four parallel galleries, assembled in a serried group; and these galleries are subdivided into cells by means of saw-dust partitions. Following the example of the big Carpenter-bee, Lithurgus chrysurus knows how to avoid the laborious work of boring, when occasion offers: I find her cocoons lodged almost as often in old dormitories as in new ones. She too has the tendency to economize her strength by turning the work of her predecessors to account. I do not despair of seeing her adopt the reed if, one day, when I possess a large enough colony, I decide to try this experiment on her. I will say nothing about L. cornutus, whom I only once surprised at her carpentering.
The Anthophorae, those children of the precipitous earthy banks, show the same thrifty spirit as the other members of the mining corporation. Three species, A. parietina, A. personata and A. pilipes, dig long corridors leading to the cells, which are scattered here and there and one by one. These passages remain open at all seasons of the year. When spring comes, the new colony uses them just as they are, provided that they are well preserved in the clayey mass baked by the sun; it increases their length if necessary, runs out a few more branches, but does not decide to start boring in new ground until the old city, which, with its many labyrinths, resembles some monstrous sponge, is too much undermined for safety. The oval niches, the cells that open on those corridors, are also profitably employed. The Anthophora restores their entrance, which has been destroyed by the insect's recent emergence; she smooths their walls with a fresh coat of whitewash, after which the lodging is fit to receive the heap of honey and the egg. When the old cells, insufficient in number and moreover partly inhabited by diverse intruders, are all occupied, the boring of new cells begins, in the extended sections of the galleries, and the rest of the eggs are housed. In this way, the swarm is settled at a minimum of expense.
To conclude this brief account, let us change the zoological setting and, as we have already spoken of the Sparrow, see what he can do as a builder. The simplest form of his nest is the great round ball of straw, dead leaves and feathers, in the fork of a few branches. It is costly in material, but can be set up anywhere, when the hole in the wall or the shelter of a tile are lacking. What reasons induced him to give up the spherical edifice? To all seeming, the same reasons that led the Osmia to abandon the Snail-shell's spiral, which requires a fatiguing expenditure of clay, in favour of the economical cylinder of the reed. By making his home in a hole in the wall, the Sparrow escapes the greater part of his work. Here, the dome that serves as a protection from the rain and the thick walls that offer resistance to the wind both become superfluous. A mere mattress is sufficient; the cavity in the wall provides the rest. The saving is great; and the Sparrow appreciates it quite as much as the Osmia.
This does not mean that the primitive art has disappeared, lost through neglect; it remains an ineffaceable characteristic of the species, ever ready to declare itself should circumstances demand it. The generations of to-day are as much endowed with it as the generations of yore; without apprenticeship, without the example of others, they have within themselves, in the potential state, the industrial aptitude of their ancestors. If aroused by the stimulus of necessity, this aptitude will pass suddenly from inaction to action. When, therefore, the Sparrow still from time to time indulges in spherical building, this is not progress on his part, as is sometimes contended; it is, on the contrary, a retrogression, a return to the ancient customs, so prodigal of labour. He is behaving like the Osmia who, in default of a reed, makes shift with a Snail-shell, which is more difficult to utilize but easier to find. The cylinder and the hole in the wall stand for progress; the spiral of the Snail-shell and the ball-shaped nest represent the starting-point.
I have, I think, sufficiently illustrated the inference which is borne out by the whole mass of analogous facts. Animal industry manifests a tendency to achieve the essential with a minimum of expenditure; after its own fashion, the insect bears witness to the economy of energy. On the one hand, instinct imposes upon it a craft that is unchangeable in its fundamental features; on the other hand, it is left a certain latitude in the details, so as to take advantage of favourable circumstances and attain the object aimed at with the least possible expenditure of time, materials and work, the three elements of mechanical labour. The problem in higher geometry solved by the Hive-bee is only a particular case—true, a magnificent case,—of this general law of economy which seems to govern the whole animal world. The wax cells, with their maximum capacity as against a minimum wall-space, are the equivalent, with the superaddition of a marvellous scientific skill, of the Osmia's compartments in which the stonework is reduced to a minimum through the selection of a reed. The artificer in mud and the artificer in wax obey the same tendency: they economize. Do they know what they are doing? Who would venture to suggest it in the case of the Bee grappling with her transcendental problem? The others, pursuing their rustic art, are no wiser. With all of them, there is no calculation, no premeditation, but simply blind obedience to the law of general harmony.
CHAPTER 8. THE LEAF-CUTTERS.
It is not enough that animal industry should be able, to a certain extent, to adapt itself to casual exigencies when choosing the site of a nest; if the race is to thrive, something else is required, something which hide-bound instinct is unable to provide. The Chaffinch, for instance, introduces a great quantity of lichen into the outer layer of his nest. This is his method of strengthening the edifice and making a stout framework in which to place first the bottom mattress of moss, fine straw and rootlets and then the soft bed of feathers, wool and down. But, should the time-honoured lichen be lacking, will the bird refrain from building its nest? Will it forgo the delight of hatching its brood because it has not the wherewithal to settle its family in the orthodox fashion?