AN EXCHANGE OF NESTS

Let us continue our series of experiments on Chalicodoma muraria. From its position on a stone which one can move at will, its nest lends itself to very interesting trials. This is the first of them. I change the place of a nest by carrying the pebble it is placed on some couple of yards away. Edifice and base forming but one, the move was made without at all disturbing the cells. I set the pebble in an open place well in sight, as it was before. When the bee returned, she could not fail to see it.

After a few minutes the owner arrived and went straight where the nest used to be. She hovered gently just above the vacant spot, looked, and alighted just where the stone used to lie. There she walked about, searching pertinaciously, then soared up and flew away. Her absence was short; she came back speedily and resumed her search on foot or on the wing—always on the spot formerly occupied by the nest. A new fit of irritation expressed by a sudden flight through the osier bed, then as sudden a return and resumption of the vain search—always over the impression left by the pebble which I had carried away. These sudden flights, prompt returns, and obstinate examinations of the empty place, were repeated very many times before the mason bee could believe her nest was gone. She certainly must have seen it in its new position, for sometimes she flew only a few inches above it, but she did not care about it. For her it only represented the nest of another bee.

Often the experiment ends without so much as a visit to the stone carried three or four yards away; the bee departs and does not return. If the distance be less—say a yard—sooner or later she alights on the pebble on which her nest is built. She will visit the cell which she was making or storing a little while earlier, plunge in her head several times, examine the surface of the stone narrowly, and after much hesitation return to search over the original spot. The nest, which is no longer in its right place, is altogether abandoned, though it be but a yard away. Vainly does the bee alight on it; she cannot recognise it as hers. I convinced myself of this by finding it several days later in just the same state as when I moved it. The cell, half filled with honey, was still open, allowing the ants to pillage it; the cell in process of construction was unfinished, without a single new course of mortar. Of course the bee may have returned, but she had not resumed her work. The displaced abode was abandoned for ever.

I shall not deduce the strange paradox that a bee, capable of returning home from a great distance, is yet incapable of finding it a yard off; the interpretation [308]of the facts does not involve this. The conclusion appears to be that she retains a tenacious impression of the spot occupied by the nest, returning there with an indefatigable obstinacy when the nest is gone. But of the nest itself she has a very vague notion—does not recognise her own masonry kneaded with her own saliva, nor the honey paste she had collected. Vainly does she visit her work, the cell; she abandons it, not acknowledging it any more, since the place where lies the pebble is no longer the same.

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, [309]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 [310]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 [311]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 [312]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 [313]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 [314]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 [315]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 [316]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.