Part 16

Now from the very first a suspicious something caught my attention. If a scholar were sent to plant a distant stake I saw him frequently pause, stoop, rise, seek about, and stoop again, forgetful of straight line and of signals. Another, whose work it was to pick up pegs, forgot the iron spike and took a pebble instead; and a third, deaf to the measurements of the angle, crumbled up a clod. The greater number were caught licking a bit of straw, and polygons stood still, and diagonals came to grief. What could be the mystery? I inquired, and all was explained. Searcher and observer born, the scholar was well aware of what the master was ignorant of—namely, that a great black bee makes earthen nests on the pebbles of the harmas, and that in these nests there is honey. My surveyors were opening and emptying the cells with a straw. I was instructed in the proper method. The honey, though somewhat strong-flavoured, is very acceptable; I in turn acquired a taste for it, and joined the nest-hunters. Later, the polygon was resumed. Thus it was that for the first time I saw Réaumur’s Mason Bee, knowing neither its history nor its historian.

This splendid Hymenopteron, with its dark violet wings and costume of black velvet, its rustic constructions on the sun-warmed pebbles among the thyme, its honey, which brought diversion from the severities of compass and square, made a strong impression on my mind, and I wished to know more about it than my pupils had taught me—namely, how to rob the cells of their honey with a straw. Just then my bookseller had for sale a magnificent work on insects, The Natural History of Articulated Animals, by de Castelnau, E. Blanchard, and Lucas. It was enriched with many engravings which caught the eye. But alas, it had a price—such a price! What did that matter? My 700 francs ought surely to suffice for everything—food for the mind as well as for the body. That which I bestowed on the one I retrenched from the other—a balance of accounts to which whoever takes science for a livelihood must needs resign himself. The purchase was made. That day I bled my university stipend abundantly; I paid away a whole month of it. It took a miracle of parsimony to fill up the enormous deficit.

The book was devoured—I can use no other word. There I learned the name of my black bee, and there I read for the first time details of the habits of insects, and found, with what seemed to my eyes an aureole round them, the venerated names of Réaumur, Huber, Léon Dufour; and while I turned the pages for the hundredth time, a voice whispered vaguely, “Thou too shalt be a historian of animals!” Naïve illusions! where are you? But let us banish these recollections, both sweet and sad, and come to the doings of our black bee.

Chalicodoma, house of pebbles, rough-cast mortar, a name which would be perfect did it not look odd to any one not well up in Greek. It is a name applied to those Hymenoptera that build cells with materials such as we use for our dwellings. It is masonry, but made by a rustic workman, better used to dried clay than to hewn stone. A stranger to scientific classification (and this causes great obscurity in some of his memoirs), Réaumur called the worker after the work, and named our builders in dried clay Mason Bees, which paints them exactly. We have two kinds, C. muraria, whose history is admirably given by Réaumur, and C. sicula, which is not special to the land of Etna, as the name suggests, but is found in Greece, Algeria, and the Mediterranean region of France, especially in the department of Vaucluse, where in May it is one of the most common Hymenoptera. The two sexes of C. muraria are so unlike in colouring that a novice observing both coming out of the same nest would take them for strangers to one another. The female is of a splendid velvet black, with dark violet wings; in the male the black velvet is replaced by a bright iron-red fleece. The second species—a much smaller one—has not this difference of colour, both sexes wearing the same costume—a general mixture of brown, red, and ashy tints. Both begin to build in the beginning of May. The wing-tips, washed with violet on a bronze ground, faintly recall the rich purple of the first species.

As Réaumur tells us, C. muraria in the northern provinces chooses as the place to fix her nest a wall well exposed to the sun and not plastered, as the plaster might come off and endanger her cells. She only entrusts her constructions to a solid foundation, such as a bare stone. I see that she is equally prudent in the south, but, for some reason unknown to me, she generally chooses some other base than the stone of a wall. A rolled pebble, often hardly larger than one’s fist,—one of those with which the waters of the glacial period covered the terraces of the Rhône valley,—is her favourite support. The great ease with which such a one is found may influence her; all our slightly raised plateaux, all our arid thyme-clad ground, are but heaped pebbles cemented with red earth. In the valleys the bee can also use the stones gathered in torrent beds; near Orange, for instance, her favourite spots are the alluviums of the Aygues, with their stretches of rolled boulders no longer visited by water. Or if a pebble be wanting, she will establish her nest on a boundary stone or an enclosing wall.

Chalicodoma sicula has a yet greater variety of choice. Her favourite position is under a tile projecting from the edge of a roof. There is scarcely a little dwelling in the fields that does not thus shelter her nests. There, every spring, she establishes populous colonies, whose masonry, transmitted from one generation to another, and yearly enlarged, finally covers a very considerable surface. I have seen such a one under the tiles of a shed, which spread over five or six square yards. When the colony were hard at work, their number and humming fairly made one dizzy. The underpart of a balcony pleases them equally, or the frame of an unused window,—above all, if closed by a sun-shutter, which offers a free passage. But these are great meeting-places, where labour, each for herself, hundreds and thousands of workers. If alone, which not seldom occurs, Chalicodoma sicula establishes herself in the first little spot she can find, so long as it has a solid basis and heat. As for the nature of this basis it matters little. I have seen nests built on bare stones and brick, on a shutter, and even on the glass panes in a shed. One thing only does not suit the bee—namely, the stucco of our houses. Prudent, like her retainer C. muraria, she would fear ruin to her cells did she entrust them to a support which might fall.

Finally, for reasons which I cannot yet satisfactorily explain, C. sicula often entirely changes her manner of building, turning her heavy mortar dwelling, which seems to require a rock to support it, into an aerial one, hung to a bough. A bush in a hedge,—no matter what—hawthorn, pomegranate, or Paliurus,—offers a support, usually about the height of a man, Ilex and elm give a greater height. The bee chooses in some thicket a bough about as thick as a straw, and constructs her edifice on this narrow base with the same mortar which would be used under a balcony or the projecting edge of a roof. When finished, the nest is a ball of earth, traversed literally by the bough. If made by a single insect it is the size of an apricot, and of a fist if several have worked at it; but this seldom occurs.

Both species use the same materials, a calcareous clay, mixed with a little sand and kneaded with the mason’s own saliva. Damp spots which would facilitate labour and spare saliva to mix mortar are disdained by the Chalicodoma, which refuses fresh earth for building, just as our builders refuse old plaster and lime. Such materials when soaked with humidity would not hold properly. What is needed is a dry powder, which readily absorbs the disgorged saliva, and forms with the albuminous principles of this liquid a kind of Roman cement, hardening quickly,—something like what we obtain with quicklime and white of egg.

A beaten road, formed of calcareous boulders crushed by passing wheels into a smooth surface like paving stones, is the quarry whence Chalicodoma sicula prefers to get mortar; whether she builds on a branch, in a hedge, or under the jutting roof of some rural habitation, it is always from a neighbouring path, or a road, or the highway, that she seeks materials—indifferent to the constant passing of beasts and travellers. You should see the active bee at work when the road is dazzling white in the hot sunshine. Between the neighbouring farm where she is building and the road where the mortar is prepared, there is the deep hum of the bees perpetually crossing each other as they come and go. The air seems traversed by constant trails of smoke, so rapid and direct is their flight. Those who go carry away a pellet of mortar as big as small shot; those who come settle on the hardest and driest spots. Their whole body vibrates as they scratch with the tips of their mandibles, and rake with their forefeet to extract atoms of earth and grains of sand, which, being rolled between their teeth, become moist with saliva and unite. They work with such ardour that they will let themselves be crushed under the foot of a passer-by rather than move. Chalicodoma muraria, however, which seeks solitude, far from human habitation, is rarely seen on beaten paths; perhaps they are too distant from the places where she builds. If she can find dry earth, rich in small gravel, near the boulder chosen as the basis of her nest, she is contented. She may either make quite a new nest in a spot hitherto unoccupied, or over the cells of an old one, after repairing them. Let us consider the first case.

After choosing a boulder, she comes with a pellet of mortar in her mandibles, and arranges it in a ring on the surface of the pebble. The forefeet, and above all the mandibles, which are her most important tools, work the material, which is kept plastic by the gradually disgorged saliva. To consolidate the unbaked clay, angular pieces of gravel, as large as a small bean, are worked in singly on the outside of the still soft mass. This is the foundation of the edifice. Other layers are added until the cell has the required height of three or four centimetres. The masonry is formed by stones laid on one another and cemented with lime, and can stand comparison with our own. True, to economise labour and mortar, the bee uses coarse materials,—large bits of gravel, which in her case answer to hewn blocks. They are chosen singly—very hard ones, almost always with angles which, fitted together, give mutual support, and add solidity to the whole. Layers of mortar, sparingly used, hold them together. The outside of the cell thus assumes the look of a piece of rustic architecture, in which stones project with their natural inequalities; but over the inside, which requires a smoother surface in order not to wound the tender skin of the larva, is spread a wash of pure mortar—artlessly, however, as if by broad sweeps of a trowel; and when it has eaten up its honey paste, the grub takes care to make a cocoon and hang the rude wall of its abode with silk. The Anthophora and Halictus, whose larvæ spin no cocoon, varnish the inside of their earthen cells delicately, giving them the polish of worked ivory.

The construction, the axis of which is always nearly vertical, with an orifice opening upward, so that the fluid honey may not run out, differs a little in form, according to its basis. On a horizontal surface it rises like a little oval tower; on a vertical or slanting one it resembles half a thimble cut down its length. In this case the support—the pebble itself—completes the surrounding wall. The cell completed, the bee sets to work at once to store it. The neighbouring flowers, especially those of Genista scorpius, which in May turn the alluviums of the torrents golden, furnish sugared liquid and pollen. She comes with her crop swelled with honey, and all yellow underneath with pollen dust, and plunges head first into the cell, where for some moments one may see her work her body in a way which tells that she is disgorging honey. Her crop emptied, she comes out, but only to go in again at once—this time backwards. With her two hind feet she now frees herself from her load, of pollen by brushing herself underneath. Again she goes out, and returns head first. She must stir the materials with her mandibles for a spoon, and mix all thoroughly together. This labour of mixing is not repeated after every journey, but only from time to time, when a considerable quantity has been collected. When the cell is half full, it is stored; an egg must be laid on the honey paste, and the door has to be closed. This is all done without delay. The orifice is closed by a cover of undiluted mortar, worked from the circumference to the centre. Two days at most seem required for the whole work, unless bad weather or a cloudy day should interrupt it. Then, backing on the first cell, a second is built and stored in the same way, and a third and fourth, etc., follow, each one with honey and an egg, and closed before another is begun. Work once begun is continued until it is completed, the bee never building a new cell until the four acts required to perfect the preceding one are performed—namely, construction, provisioning, an egg, and sealing the cell.

As Chalicodoma muraria always works alone on her chosen boulder, and shows great jealousy if her neighbours alight there, the number of cells clustered on one pebble is not great—usually six to ten. Are some eight larvæ her whole progeny, or will she establish a more numerous family on other boulders? The surface of the stone would allow of more cells if she had eggs for them, and the bee might build there very comfortably without hunting for another, or leaving the one to which she is attached by habit and long acquaintance. I think, therefore, that most probably all her scanty family are settled on the same stone—at all events when she builds a new abode.

The six or ten cells composing the group are certainly a solid dwelling, with their rustic covering of gravel, but the thickness of their walls and lids—two millimetres at most—hardly seems sufficient against rough weather. Set on its stone in the open air, quite unsheltered, the nest will undergo the heat of summer suns which will turn every cell into an oven; then will come the autumn rains which will slowly eat away the masonry, and then winter frosts which will crumble what the rain may have respected. However hard the cement may be, can it resist all these attacks, and if it can, will not the larvæ, sheltered by so thin a wall, suffer from over-heat in summer and too keen cold in winter?

Without having gone through all these arguments, the bee acts wisely. When all the cells are completed she builds a thick cover over the whole group, which, being of a material impermeable to water and almost a non-conductor, is at once a defence against heat and cold and damp. This material is the usual mortar, made of earth and saliva, only with no small stones in it. The bee lays it on,—one pellet after another, one trowelful and then a second,—till there is a layer a centimetre thick over all the cells, which disappear entirely under it. The nest is now a rude dome, about as big as half an orange; one would take it for a clod of mud, half crushed by being flung against a stone where it had dried. Nothing outside betrays its contents—no suggestion of cells—none of labour. To the ordinary eye it is only a chance splash of mud.

This general cover dries as rapidly as do our hydraulic cements, and the nest is almost as hard as a stone. A knife with a strong blade is needed to cut it. In its final shape the nest recalls in no degree the original work; one would suppose the elegant turrets adorned with pebble work, and the final dome, looking like a bit of mud, to be the work of two different species. But scratch away the cover of cement and we recognise the cells and their layers of tiny pebbles. Instead of building on a boulder yet unoccupied, Chalicodoma muraria likes to utilise old nests which have lasted through the year without notable injury. The mortared dome has remained much as it was at the beginning, so solid was the masonry; only it is pierced by a number of round holes corresponding to the chambers inhabited by the larvæ of the past generation. Such dwellings, only needing a little repair to put them in good condition, economise much time and toil; so Mason Bees seek them, and only undertake new constructions when old nests fail them.

From the same dome come forth brothers and sisters—reddish males and black females—all descendants of the same bee. The males lead a careless life, avoiding all labour, and only returning to their clay dwellings for a brief courtship of their ladies; and they care nothing for the deserted dwelling. What they want is nectar from flower-cups, not mortar between their mandibles. But there are the young mothers, who have sole charge of the future of the family—to which of them will fall the inheritance of the old nest? As sisters they have an equal right to it—so would human justice decide, now that it has made the enormous progress of freeing itself from the old savage right of primogeniture; but Mason Bees have not got beyond the primitive basis of property—the right of the first comer.

So when the time to lay has come, a bee takes the first free nest which suits her and establishes herself there, and woe to any sister or neighbour who thenceforward disputes possession of it. A hot reception and fierce pursuit would soon put the new-comer to flight; only one cell is wanted at the moment out of all which gape like little wells around the dome, but the bee calculates that by and by the rest will be useful, and she keeps a jealous watch on them all and drives away every visitor. I cannot remember having seen two Mason Bees working on the same pebble.

The work is now very simple. The bee examines the inside of the old cell to see where repairs are needed, tears down the rags of cocoon hanging on the walls, carries out the bits of earth fallen from the vault pierced by the inhabitant in order to get out, mortars any places out of repair, mends the orifice a little, and that is all. Then comes storage, laying an egg, and stopping up the cell. When these are successively completed, the general cover, the mortar dome, is repaired if necessary, and all is finished.

Chalicodoma sicula prefers a sociable life to a solitary one, and hundreds—nay, several thousands—will establish themselves on the under surface of the tiles on a hovel, or the edge of a roof. It is not a real society with common interests, dear to all, but merely a gathering where each works for herself and is not concerned for the rest—a throng recalling the swarm of a hive only by their number and industry. They use the same mortar as Chalicodoma muraria, equally resistant and waterproof, but finer and without pebbles. First the old nests are utilised. Every free cell is repaired, stored, and shut up. But the old ones are far from sufficing to the population, which increases rapidly year by year, and on the surface of the nest, where the cells are hidden below the old general mortar covering, new ones are built as required. They are placed more or less horizontally, one beside another, with no kind of order. Every constructor builds as the fancy takes her, where and as she wills; only she must not interfere with her neighbour’s work, or rough treatment will soon call her to order. The cells accumulate in chance fashion in this workyard, where there is no general plan whatever. Their form is that of a thimble divided down the axis, and their enclosure is completed either by adjacent cells, or the surface of the old nest. Outside they are rough, and look like layers of knotted cords corresponding to the layers of mortar. Inside the walls are level but not smooth; a cocoon will replace the absent polish.

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.

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.

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 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 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 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.