Insect Architecture

by James Rennie

The distance to which they carried the clay was probably considerable, as there was no wall near, in the direction they all flew towards, upon which they could build; and in the same direction also, it is worthy of remark, they could have procured much nearer the very same sort of clay. Whatever might be the cause of their preference, we could not but admire their extraordinary industry. It did not require more than half a minute to knead one of the pellets of clay; and, from their frequent returns, probably not more than five minutes to carry it to the nest, and apply it where wanted. From the dryness of the weather, indeed, it was indispensable for them to work rapidly, otherwise the clay could not have been made to hold together. The extent of the whole labour of forming a single nest may be imagined, if we estimate that it must take several hundred pellets of clay for its completion. If a bee work fourteen or fifteen hours a-day, therefore, carrying ten or twelve pellets to its nest every hour, it will be able to finish the structure in about two or three days; allowing some hours of extra time for the more nice workmanship of the cells in which the eggs are to be deposited, and the young grubs reared.

That the construction of such a nest is not a merely agreeable exercise to the mason-bee has been sufficiently proved by M. Du Hamel. He has observed a bee (Megachile muraria) less careful to perform the necessary labour for the protection of her offspring than those we have described, but not less desirous of obtaining this protection, attempt to usurp the nest which another had formed. A fierce battle was invariably the consequence of this attempt; for the true mistress would never give place to the intruder. The motive for the injustice and the resistance was an indisposition to further labour. The trial of strength was probably, sometimes, of as little use in establishing the right as it is amongst mankind; and the proper owner, exhausted by her efforts, had doubtless often to surrender to the dishonest usurper.

The account which Réaumur has given of the operations of this class of bees differs considerably from that which we have here detailed; from the species being different, or from his bees not having been able to procure moist clay. On the contrary, sand was the chief material used by the mason-bees (Megachile muraria); which they had the patience to select from the walks of a garden, and knead into a paste or mortar, adapted to their building. They had consequently to expend a much greater quantity of saliva than our bees (Osmia bicornis), which worked with moist clay. Réaumur, indeed, ascertained that every individual grain of sand is moistened previous to its being joined to the pellet, in order to make it adhere more effectually. The tenacity of the mass is, besides, rendered stronger, he tells us, by adding a proportion of earth or garden-mould. In this manner, a ball of mortar is formed, about the size of a small shot, and carried off to the nest. When the structure of this is examined, it has all the appearance externally of being composed of earth and small stones or gravel. The ancients, who were by no means accurate naturalists, having observed bees carrying pellets of earth and small stones, supposed that they employed these to add to their weight, in order to steady their flight when impeded by the wind.

The nests thus constructed appear to have been more durable edifices than those which have fallen under our observation;—for Réaumur says they were harder than many sorts of stone, and could scarcely be penetrated with a knife. Ours, on the contrary, do not seem harder than a piece of sun-baked clay, and by no means so hard as brick. One circumstance appeared inexplicable to Réaumur and his friend Du Hamel, who studied the operations of these insects in concert. After taking a portion of sand from one part of the garden-walk, the bees usually took another portion from a spot almost twenty and sometimes a hundred paces off, though the sand, so far as could be judged by close examination, was precisely the same in the two places. We should be disposed to refer this more to the restless character of the insect than to any difference in the sand. We have observed a wasp paring the outside of a plank, for materials to form its nest; and though the plank was as uniform in the qualities of its surface, nay, probably more so than the sand could be, the wasp fidgeted about, nibbling a fibre from one, and a fibre from another portion, till enough was procured for one load. In the same way, the whole tribe of wasps and bees flit restlessly from flower to flower, not unfrequently revisiting the same blossom, again and again, within a few seconds. It appears to us, indeed, to be far from improbable, that this very restlessness and irritability may be one of the springs of their unceasing industry.

By observing, with some care, the bees which we found digging the clay, we discovered one of them (Osmia bicornis) at work upon a nest, about a gunshot from the bank. The place it had chosen was the inner wall of a coal-house, facing the south-west, the brick-work of which was but roughly finished. In an upright interstice of half an inch in width, between two of the bricks, we found the little architect assiduously building its walls. The bricklayer’s mortar had either partly fallen out, or been removed by the bee, who had commenced building at the lower end, and did not build downwards, as the social wasps construct their cells.

The very different behaviour of the insect here, and at the quarry, struck us as not a little remarkable. When digging and preparing the clay, our approach, however near, produced no alarm; the work went on as if we had been at a distance; and though we were standing close to the hole, this did not scare away any of the bees upon their arrival to procure a fresh load. But if we stood near the nest, or even in the way by which the bee flew to it, she turned back or made a wide circuit immediately, as if afraid to betray the site of her domicile. We even observed her turning back, when we were so distant that it could not reasonably be supposed she was jealous of us; but probably she had detected some prowling insect depredator, tracking her flight with designs upon her provision for her future progeny. We imagined we could perceive not a little art in her jealous caution, for she would alight on the tiles as if to rest herself; and even when she had entered the coal-house, she did not go directly to her nest, but again rested on a shelf, and at other times pretended to examine several crevices in the wall, at some distance from the nest. But when there was nothing to alarm her, she flew directly to the spot, and began eagerly to add to the building.

It is in instances such as these, which exhibit the adaptation of instinct to circumstances, that our reason finds the greatest difficulty in explaining the governing principle of the minds of the inferior animals. The mason-bee makes her nest by an invariable rule; the model is in her mind, as it has been in the mind of her race from their first creation: they have learnt nothing by experience. But the mode in which they accomplish this task varies according to the situations in which they are placed. They appear to have a glimmering of reason, employed as an accessary and instrument of their instinct.

Cells of Mason-Bees, built, in the first and second figures, by Osmia bicornis between bricks, and in the third, by Megachile muraria in the fluting of an old pilaster.—About half the natural size.

The structure, when finished, consisted of a wall of clay supported by two contiguous bricks, enclosing six chambers, within each of which a mass of pollen, rather larger than a cherry-stone, was deposited, together with an egg, from which in due time a grub was hatched. Contrary to what has been recorded by preceding naturalists with respect to other mason-bees, we found the cells in this instance quite parallel and perpendicular; but it may also be remarked, that the bee itself was a species altogether different from the one which we have described above as the Anthophora retusa, and agreed with the figure of the one we caught quarrying the clay—(Osmia bicornis).