Part 18

We must own that insect memory is a strange one, so lucid in general knowledge of locality, so limited as to its home. I should be disposed to name it topographical instinct; the creature knows the localities, but not the dear nest—the dwelling. The Bembex led us to a like conclusion. The nest being laid open, she cared nothing for the family—for the larva writhing distressfully in the sun unrecognised. What they do recognise, what they seek, and find with marvellous precision, is the place where no longer exists anything of the entrance door—not even a threshold.

If any doubt remain as to the powerlessness of Chalicodoma muraria to know her nest except by the place which the pebble occupies on the ground, this may set it at rest. I substituted a nest of one mason bee for that of another, as alike as might be, both in masonry and storage. Of course this exchange and those of which I shall speak later were made during the absence of the owner. In the nest not hers, but placed where her own had been, she established herself without hesitation. If she had been building, I offered her a cell in process of construction, and she worked on with the same care and zeal as if the work already done had been her own. If she were bringing honey and pollen, I offered a cell partly stored. Her journeys continued, with honey in her crop and pollen underneath her body to complete filling the store of another bee.

Thus the bee does not suspect the exchange, nor distinguish what is and is not hers. She thinks she is continuing to work at a cell really her own.

After leaving her for a time in possession of the exchanged nest, I restored her own. The fresh change passed unobserved; her labour was continued in the cell restored to her, at the point at which it had arrived in the substituted one. Then I once more substituted the strange nest, and still she persisted in her labour. Thus alternating nests at the same spot, I thoroughly convinced myself that the insect cannot perceive the difference between that which is her own and that which is not. Whether the cell be hers or not, she works with equal fervour, provided that the basis for the edifice—the stone—remains in its original position.

One may lend a livelier interest to the experiment by using two neighbouring nests—work at which is about equally advanced. I transpose them, placing one where the other was; the distance is hardly a cubit. Despite this close neighbourhood, which allows the bees to see both nests at once and choose between them, the two bees on arriving each immediately alighted on the substituted nest and went on working at it. We may change the two nests at pleasure; we shall still see the two mason bees keep to the spot chosen by them and work in turn—now at their own cell, now at that of the other.

It may be thought that the confusion was caused by a close resemblance between the two nests, since, at first little expecting the results obtained, I began by choosing those as much alike as possible, lest the bees should be repelled. My caution presupposed a clear-sightedness the insect did not possess. I now took two nests exceedingly unlike, except that in each the bee found a cell advanced in its work to the same point. The first was an old nest, with the dome pierced with eight holes, the orifices of cells of a preceding generation; one of these had been restored, and the bee was storing it. The second was a new nest, with no dome, and composed of a single cell with little stones on the outside. Here too the bee was storing her paste. Certainly no two nests could differ more: the one with its eight vacant rooms, and its ample dome of clay, the other with a single cell—bare, and at most the size of an acorn.

Well, the two mason bees did not hesitate long before the two exchanged nests—hardly a yard apart. Each went to the site of its former abode. The owner of the old nest found but a single cell. She rapidly inspected the stone, and without further ceremony first plunged her head into the cell to disgorge honey, and then her hind-quarters to drop pollen. And this was no action performed to rid herself as soon as possible of a trying burden, for she flew away and quickly returned with fresh stores to be laid up. This bringing provisions to another’s larder was repeated as often as I would allow. The other bee, finding, instead of one cell a spacious building with eight chambers, was at first considerably embarrassed. Which of the eight was the right one?—in which was her heap of bee bread? She plunged down into each room, and at length found what she was seeking—a condition like that which she had left when she took her last journey, the beginning of a store of food. From that moment she behaved like her neighbour, and carried honey and pollen to a cell not made by her.

Let us restore the nests to their natural places, exchanging them afresh. Each bee, after a little hesitation, sufficiently explained by the very great difference between the two nests, will work alternately in her own cell and the strange one. At length the egg is laid and the cell closed, whichever the nest may be that she is occupied with at the moment when the provisions are sufficient. Such facts show clearly why I hesitate to give the name of memory to the singular faculty that brings back the insect so accurately to the site of her nest, yet does not allow her to distinguish her work from that of another, however great may be the difference of appearance between them.

Now let us experiment on Chalicodoma muraria from another psychological point of view. Here is a mason bee at work on the first course of her cell; in exchange I give her one not only completed, but half full of honey, which I stole from an owner who would speedily have laid an egg there. What will the mason do with this munificent gift which spares her the labour of building and storage? Leave her mortar, of course, lay an egg, and close all up. Not at all! the animal finds our logic illogical. The insect obeys an inevitable, unconscious impulse. It has no choice as to what it shall do,—no discernment as to what is and is not desirable,—but glides, as it were, down an irresistible slope prepared for it beforehand to bring it to a determined end. The facts still to be stated affirm this strongly.

The bee, which is building, and to which I offer a cell ready made and full of honey, will not give up building for that; she is following her trade as mason, and once on that tack, led on by unconscious impulse, she must needs build, even if her labour be superfluous and contrary to her interests. The cell I give her is certainly quite complete in the opinion of its own constructor, since the bee from whom I subtracted it was finishing the store of honey. To touch it up, and, above all, to add to it is useless and absurd. All the same the bee which is building will build. On the orifice of the honey store she lays another layer of mortar, then another and another, until the cell is actually a third beyond its usual height. Now the task is done—not as well indeed as if the bee had continued the cell whose foundations she was laying when the nests were exchanged, but certainly in a way more than enough to demonstrate the irresistible impulse which drove the builder on. Then came the storing, likewise abridged, for otherwise the honey would overflow by the union of the stores of two bees. Thus the mason bee, which is beginning to build, and to which one gives a cell completed and filled with honey, alters nothing in the order of her work. First she builds and then she stores; only she shortens her labours—instinct warning her that the height of the cell and quantity of honey are beginning to assume proportions too great.

The reverse of this is not less conclusive. To a mason bee which was laying up food I would give a cell only just sketched out and unable to receive the honey paste. This cell, still damp from the constructor’s saliva, might or might not be accompanied by other cells, recently closed and containing an egg and honey. The bee, whose half-filled cell is thus replaced, seems greatly puzzled on arriving with her load at this shallow hollow offering no place for the honey. She will examine it, measure it with her eye, try it with her antennæ, and recognise its insufficient depth. For a time she hesitates, departs, returns, flies off again, and comes back in haste to dispose of her load. Her embarrassment is visible; I could not help saying inwardly: “Take some mortar—take some mortar, and finish your storehouse. It will only require a few moments to make it deep enough.” The bee was of a different opinion. She was laying in food, and food she must lay up, happen what might. She could not decide to lay aside the pollen brush for the mason’s trowel, and nothing could induce her to delay the harvest which occupied her in order to take up that work of building for which it is not the due moment. Rather would she seek another cell, in the desired condition, and will penetrate there to store the honey, even if received with fury by the owner. In fact, this happened. I wished her success, knowing myself to be the cause of this desperate act. My curiosity had turned an honest worker into a thief.

Matters may take a yet more serious turn, so obstinate and imperious is the desire to harvest the store securely. The unfinished cell that the bee refuses to accept instead of her own complete one, with its honey, is sometimes, as I have said, among several containing paste and egg, and newly closed. In this case I have seen, though not always, the following sight. Having ascertained unmistakably that the unfinished cell will not do, the bee begins to gnaw the cover of a neighbouring one. With her saliva she softens a spot in the mortar, and patiently digs away atom by atom in the hard covering. A long half hour passes before the tiny dimple excavated is big enough to receive a pin’s head. I waited. Then I got out of patience, and, feeling sure that she wanted to open the storehouse, I decided to help her and shorten the labour. With the point of my knife I knocked off the top; but the crown of the cell came off too, and its edge was a good deal broken. In my clumsiness I had made a graceful vase into a wretched, shattered pot. I was right; the bee wanted to break open the door, and without troubling herself as to the fragmentary state of the orifice, she immediately established herself in the cell opened to her. Many times did she bring honey and pollen, though the store was already complete. Finally, in this cell containing an egg not hers she laid her own egg, and then closed, as best she could, the shattered mouth. Thus this bee, who was engaged in bringing food, neither could nor would be baffled by the impossibility brought about by me of continuing her work unless she completed the cell which replaced hers. What she was doing she persisted in doing in spite of obstacles. She accomplished her task thoroughly, but in the most absurd way,—by breaking into another bee’s cell, continuing to store in a cell already overflowing, placing an egg where the real owner had already laid one, and finally, closing an orifice which needed serious repairs. Could one desire a better proof of the irresistible impulse obeyed by the insect?

Finally, there are other rapid and consecutive actions so closely connected that the execution of the second implies necessarily the repetition of the first, even when this has become useless. I have already said how Sphex flavipennis persists in going down into her burrow alone, having brought near it the cricket which I cruelly removed immediately. Her repeated discomfitures did not make her give up the preliminary domiciliary visit, useless as it is when repeated ten or twenty times. Chalicodoma muraria exhibits under another form a like repetition of an act useless itself, but a necessary prelude to the next one. Arrived with her booty, she goes through a double act of storage. First she plunges head first into the cell to disgorge the contents of her crop; then she comes out, returning at once backward to brush off her load of pollen. At the moment when she is about to enter, tail first, I gently put her aside with a straw, thus hindering her second action. She begins all over again, going head first into the cell, although her crop is empty. Then comes the turn of going in backward. I instantly put her aside again, and again she goes in head first. Once more I use my straw. And this goes on as long as the observer pleases. Put aside just as she is about to introduce her hinder parts into the cell, she returns to the orifice and persists in descending head first. Sometimes she goes quite down—sometimes only half-way, or perhaps there is a mere pretence at descending, and she only stoops her head in the opening, but at any rate this quite useless action—for the honey is already disgorged—invariably precedes the entrance backward to deposit pollen. It is almost the movement of a machine, not a wheel of which moves till the main one begins to turn.

DESCRIPTIVE NOTES

The following Hymenoptera appear new to me in the French fauna. I append their description:—

Cerceris antoniæ, H. Fab.

Length—16–18 millimetres. Black, closely and strongly punctured; clypeus raised like a nose, i.e. forming a convex projection, large at the base, pointed at the end—like half a cone cut down its length; crest between the antennæ projecting; a line above crest, cheeks, and a large dot behind each eye, yellow; hood—yellow with black point; mandibles, rusty yellow; tips, black. The 4th and 5th joints of antennæ, rusty yellow, the rest brown. Two dots on prothorax, wing scales and postscutellum, yellow; first segment of abdomen with two dot-like spots; four next on posterior edge having a yellow band sharply hollowed in triangle form, or even broken, and this the more as the segment is a less distant one.

Under part of the body, black; feet entirely of rusty yellow colour; wings slightly bronzed at tip. Female. Male unknown to me.

In colouring this species approaches Cerceris labiata, from which, however, it differs remarkably in the form of the clypeus and the much larger size of the insect. Observed round Avignon in July. I dedicate this species to my daughter Antonia, whose help has often been valuable to me in my entomological researches.

Cerceris julii, H. Fab.

Length—7–9 millimetres. Black, closely and strongly punctured; clypeus flat; face covered with a fine silvery pubescence; a narrow yellow band on each side, on the inner edge of the eyes; mandibles—yellow with brown tips; antennæ—black above, pale red below; lower face of their basal joint, yellow. Two small distant points on the prothorax; scales of wings and postscutellum, yellow. A yellow band on third segment of the abdomen, and another on the fifth; these two are deeply hollowed on the anterior edge—the first in a semicircle, the second in a triangle.

Under part of the body all black; coxæ black; thighs of the hinder pair of legs quite black; those of the two anterior pairs, black at base, yellow at the ends; legs and tarsi, yellow; wings rather smoke-coloured. Female.—Var. (1) Prothorax without yellow dots; (2) two small yellow dots on second segment of abdomen; (3) wider yellow band on inner side of the eyes; (4) front of clypeus edged with yellow.

Male unknown to me. This Cerceris, the smallest of my part of France, feeds its larvæ on the smallest kinds of weevils (Bruchus granarius and Apion gravidum). Observed round Carpentras, where it builds in September in soft sandstone—locally called safre.

Bembex julii, H. Fab.

Length—18–20 millimetres. Black, with bristling whitish hairs on head, thorax, and base of first segment of the abdomen; labrum lengthened, yellow; clypeus, with a sloping ridge, forming as it were an angle of three sides—one face—that of the outer edge—is all yellow, while each of the two others is marked with a large rectangular black patch bordering on its neighbour, and thus forming a stripe; both marks, as well as the cheeks, are covered with a fine silvery down; cheeks on line between the antennæ, yellow; posterior edge of eyes with a long yellow border; mandibles—yellow, with brown tips; two first joints of antennæ yellow beneath, black above, the rest black; prothorax—black; sides and dorsal division, yellow; mesothorax—black; the callous point, and a small one on each side above the base of the intermediate feet, yellow; metathorax—black, with two yellow dots behind, and a larger one on each side above the base of the hind feet. The two first dots are sometimes wanting.

Abdomen—bright black above and without hairs, except at the base of the first segment, which bristles with whitish ones. All the segments have a wavy transverse band, wider on the sides than in the middle, and approaching the posterior edge in proportion as the segment is further back. On the fifth segment the yellow band reaches the posterior edge. Anal segment—yellow, black at the base, bristling all over the dorsal surface with papillæ of a rusty red, which serve as base to the hairs. A row of like hair-bearing tubercules occupies also the posterior edge of the fifth segment. Below, the abdomen is a brilliant black, with a triangular yellow mark on each side of the four intermediate segments.

Coxæ—black; thighs yellow in front, black behind; legs and tarsi—yellow; wings transparent.

Male.—The zig-zag mark on the clypeus is narrower, or even absent; face then entirely yellow; abdominal bands very pale yellow, almost white. The sixth segment has a band like the preceding ones, but shorter and often reduced to two dots. The second segment has underneath it a longitudinal keel, raised and spine-shaped behind. The anal one has below it an angular, rather thick projection. Otherwise like the female.