As soon as a cell is built it is stored and walled up, as we have seen with Chalicodoma muraria. This work goes on through the whole of May. At length all the eggs are laid, and the bees, without any distinction as to what does or does not belong to them, all set to work on a common shelter of the colony—a thick bed of mortar, filling up spaces and covering all the cells. In the end the nests look like a large mass of dry mud—very irregular, arched, thickest in the middle, the primitive kernel of the establishment, thinnest at the edges, where there are fewest cells, and very variable in extent, according to the number of workers, and consequently to the time when the nest was begun. Some are not much larger than one’s hand, while others will occupy the greater part of the edge of a roof, and be measured by square yards. [[288]]
If Chalicodoma sicula works alone, as she often does, on the shutter of an unused window or on a stone or a branch, she behaves in just the same way. For instance, if the nest is on a bough, she begins by solidly fixing the basis of her cell on the slender twig. Then the building rises into a little vertical tower. This cell being stored and ceiled, another follows, supported both by the bough and the first cell, until six to ten cells are grouped one beside the other, and finally a general cover of mortar encloses them all together with the bough, which gives them a firm foundation. [[289]]
XXI
EXPERIMENTS
Built on small pebbles which one can carry whither one will, remove, or interchange, without disturbing either the work of the constructor or the quiet of the inhabitants of the cells, the nests of Chalicodoma muraria lend themselves readily to experiment—the only method capable of throwing a little light on the nature of instinct. Profitably to study the physical faculties of the animal it is not enough to know how to turn to account such circumstances as a happy chance may offer to the observer: one must be capable of originating others, and vary them as much as possible and submit them to mutual control; in short, to give science a solid basis of fact one must experiment. Then some day will vanish before the evidence of exact documents the fantastic legends which cumber our books, such as the Scarabæus inviting his comrades to help in dragging his ball out of a rut, or a Sphex cutting up a fly to carry it in spite of the wind, and much more which is misused by those who desire to see in the animal world that which is not there. Thus, too, will materials be prepared which, used sooner or later by a learned [[290]]hand, will cast premature and baseless theories back into oblivion.
Réaumur generally confines himself to stating facts as they offered themselves to him in the normal course of things, and does not attempt to penetrate further into the powers of the insect by means of conditions brought about artificially. In his day there was everything to do, and the harvest was so great that the illustrious reaper hurried on to what was most urgent,—the gathering of it in, leading his successors to examine grain and ear in detail. Nevertheless, he mentions an experiment made on Chalicodoma muraria by his friend Du Hamel. The nest was placed in a glass funnel, the mouth of which was closed by a piece of gauze. Three males were hatched, which, though they had penetrated mortar hard as a stone, either did not attempt to pierce the thin gauze, or thought it beyond their power to do so. All three died under the glass. Insects generally only know how to execute that which they need to do in the common order of nature, adds Réaumur.
For two reasons the experiment does not satisfy me. First of all, to give gauze to be pierced by insects with tools made to pierce lumps as hard as tufa does not seem a happy idea; you cannot expect a navvy’s pickaxe to do the same work as the scissors of a seamstress. Secondly, the transparent glass prison seems ill chosen. As soon as it had opened a way through the thickness of its earthen dome, the insect found itself in daylight, and to it daylight means final deliverance and freedom. It strikes against an invisible obstacle—the glass, and glass [[291]]does not suggest an obstacle to it. Beyond, it sees a free space bathed in sunshine. It exhausts itself in efforts to fly there, unable to comprehend the uselessness of struggling against this strange, invisible barrier, and perishes, obstinate and exhausted, without a glance at the gauze which closes the conical tube. The experiment must be repeated under better conditions.
The obstacle I selected was common gray paper—opaque enough to keep the insect in the dark—thin enough not to offer serious resistance to the prisoner’s efforts. As there is a vast difference by way of obstacle between a paper partition and a vault of unbaked clay, let us see first if Chalicodoma muraria knows how, or rather if it is able, to pierce such a barrier. The two mandibles—pickaxes adapted to pierce hard mortar—are they also scissors capable of cutting thin material? That is the point to be ascertained.
In February, when the insect is already in the perfect state, I withdrew a certain number of cocoons uninjured from their cells, and placed each separately in a piece of reed, closed at one end naturally, open at the other. The pieces of reed represented the nest-cells. The cocoons were introduced so that the head of the insect should turn to the opening. Finally, my artificial cells were closed in various ways. Some had a stopper of kneaded earth, which, when dry, answered in thickness and consistency to the mortar of the nest; others were shut by a cylinder of Sorghum vulgare at least a centimetre thick, and others with a stopper of gray paper, solidly fixed by its edges. All these bits of [[292]]cane were arranged side by side, vertically, in a box, with the artificial roof at the top, so that the insects were in the exact position they had in a nest. To open them they must do as they would had I not intervened—break through the wall overhead. I protected all with a large bell glass, and awaited the month of May when they would emerge.