These, I think, are sufficient details of the fundamental distinction to be drawn in the insect’s mentality, the distinction, that is, between pure instinct and discernment. If people confuse these two provinces, as they nearly always do, any understanding becomes impossible; the last glimmer of light disappears behind the clouds of interminable discussions. From an industrial point of view, let us look upon the insect as a worker thoroughly versed from birth in a craft whose essential principles never vary; let us grant that unconscious worker a gleam of intelligence which will permit it to extricate itself from the inevitable conflict of attendant circumstances; and I think [[163]]that we shall have come as near to the truth as the state of our knowledge will allow for the moment.
Having thus assigned a due share both to instinct and to its aberrations when the course of its different phases is disturbed, let us see what discernment is able to do in the selection of a site for the nest and materials for building it; and, leaving the Pelopæus, upon whom it is useless to dwell any longer, let us consider other examples, picked from among those richest in variations.
The Mason-bee of the Sheds (Chalicodoma rufitarsis, Pérez) well deserves the name which I have felt justified in giving her from her habits: she settles in numerous colonies in our sheds, on the lower surface of the tiles, where she builds huge nests which endanger the solidity of the roof. Nowhere does the insect display a greater zeal for work than in one of these colossal cities, an estate which is constantly increasing as it passes down from one generation to another; nowhere does it find a better workshop for the exercise of its industry. Here it has plenty of room, a quiet resting-place, sheltered from damp and from excess of heat or cold. [[164]]
But the spacious domain under the tiles is not within the reach of all: sheds with free access and the proper sunny aspect are pretty rare. These sites fall only to fortune’s favourites. Where will the others take up their quarters? More or less anywhere. Without leaving the house in which I live, I can enumerate stone, wood, glass, metal, paint and mortar as forming the foundation of the nests. The green-house with its furnace heat in the summer and its bright light, equalling that outside, is fairly well-frequented. The Mason-bee hardly ever fails to build there each year, in squads of a few dozen, now on the glass panes, now on the iron bars of the framework. Other little swarms settle in the window-embrasures, under the projecting ledge of the front-door or in the cranny between the wall and an open shutter. Yet others, being perhaps of a morose disposition, flee society and prefer to work in solitude, one in the inside of a lock or of a pipe intended to carry the rain-water from the leads; another in the mouldings of the doors and windows or in the crude ornamentation of the stonework. In short, the house is made use of all round, provided that the shelter be an out-of-door one; for [[165]]observe that the enterprising invader, unlike the Pelopæus, never penetrates inside our dwellings. The case of the conservatory is an exception more apparent than real: the glass building, standing wide open throughout the summer, is to the Mason-bee but a shed a little lighter than another. There is nothing here to arouse the distrust with which anything indoors or closed inspires her. To build on the threshold of an outer door, to usurp its lock, a hiding-place to her fancy, is all that she allows herself; to go any farther is an adventure repugnant to her taste.
Lastly, in the case of all these dwellings, the Mason-bee is man’s free tenant; her industry makes use of the products of our own industry. Can she have no other establishments? She has, beyond a doubt; she possesses some constructed on the ancient plan. On a stone the size of a man’s fist, protected by the shelter of a hedge, sometimes even on a pebble in the open air, I see her building now groups of cells as large as a walnut, now domes emulating in size, shape and solidity those of her rival, the Mason-bee of the Walls.
The stone support is the most frequent, though not the only one. I have found [[166]]nests, but sparsely inhabited it is true, on the trunks of trees, in the seams of the rough bark of oaks. Among those whose support was a living plant, I will mention two that stand out above all the others. The first was built in the grooves of a Peruvian torch-thistle as thick as my leg; the second rested on a stalk of the opuntia, the Indian fig. Had the fierce armour of these two stout cactuses attracted the attention of the insect, which looked upon their tufts of spikes as furnishing a system of defence for its nest? Perhaps so. In any case, the attempt was not imitated; I never saw another installation of the kind. There is one definite conclusion to be drawn from my two discoveries. Despite the oddity of their structure, which is unparalleled in the local flora, the two American importations did not compel the insect to go through an apprenticeship of groping and hesitation. The one which found itself in the presence of those novel growths and which was perhaps the first of its race to do so took possession of their grooves and stalks just as it would have done of a familiar site. From the start, the fleshy plants from the New World suited it quite as well as the trunk of a native tree. [[167]]
The Mason-bee of the Pebbles (Chalicodoma parietina) has none of this elasticity in the choice of a site. In her case, the smooth stone of the parched uplands is the almost invariable foundation of her structures. Elsewhere, under a less clement sky, she prefers the support of a wall, which protects the nest against the prolonged snows. Lastly, the Mason-bee of the Shrubs (C. rufescens, Pérez) fixes her ball of clay to a twig of any ligneous plant, from the thyme, the rock-rose and the heath to the oak, the elm and the pine. The list of the sites that suit her would almost form a complete catalogue of the ligneous flora.
The variety of places where the insect installs itself, so eloquent of the part played by discernment in their selection, becomes still more remarkable when accompanied by a corresponding variety in the architecture of the cells. This is more particularly the case with the Three-horned Osmia,[2] who, as she uses clayey materials very easily affected by the rain, requires, like the Pelopæus, a dry shelter for her cells, a shelter which she finds ready-made and uses [[168]]just as it is, after a few touches by way of sweeping and cleansing. The homes which I see her adopt are especially the shells of Snails that have died under the stone-heaps and in the low, unmortared walls which support the cultivated earth of the hills in shelves or terraces. The use of Snail-shells is accompanied by the no less active use of the old cells of both the Mason-bee of the Sheds and of certain Anthophoræ (A. pilipes, A. parietina and A. personata.)[3]
We must not forget the reed, which is highly appreciated when—a rare find—it appears under the desired conditions. In its natural state, the plant with the mighty hollow cylinders is of no possible use to the Osmia, who knows nothing of the art of perforating a woody wall. The gallery of an internode has to be wide open before the Bee can take possession of it. Also, the clean-cut stump must be horizontal, otherwise the rain would soften the fragile edifice of clay and soon lay it low; also, the stump must not be lying on the ground and must be kept at some distance from the dampness of the soil. We see [[169]]therefore that, without the intervention of man, involuntary in the vast majority of cases and deliberate only on the experimenter’s part, the Osmia would hardly ever find a reed-stump suited to the installation of her family. It is to her a casual acquisition, a home unknown to her race before men took it into their heads to cut reeds and make them into hurdles for drying figs in the sun.
How did the work of man’s pruning-knife bring about the abandonment of the natural lodging? How was the spiral staircase of the Snail-shell replaced by the cylindrical gallery of the reed? Was the change from one kind of house to another effected by gradual transitions, by attempts made, abandoned, resumed, becoming more and more definite in their results as generation succeeded generation? Or did the Osmia, finding the cut reed that answered her requirements, install herself there straightway, scorning her ancient dwelling, the Snail-shell? These questions called for a reply; and they have received one. Let us describe how things happened.