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- Bramble-bees and Others - 4/47 -

Sometimes, again, a grub dies in its cocoon; and the cradle of the deceased, now turned into a coffin, forms an everlasting obstacle. How shall the insect cope with such grave circumstances?

Among the many bramble-stumps which I have collected, some few have presented a remarkable peculiarity. In addition to the orifice at the top, they had at the side one and sometimes two round apertures that looked as though they had been punched out with an instrument. On opening these stalks, which were old, deserted nests, I discovered the cause of these very exceptional windows. Above each of them was a cell full of mouldy honey. The egg had perished and the provisions remained untouched: hence the impossibility of getting out by the ordinary road. Walled in by the unsurmountable obstacle, the Osmia on the floor below had contrived an outlet through the side of the shaft; and those in the lower storeys had benefited by this ingenious innovation. The usual door being inaccessible, a side-window had been opened by means of the insect's jaws. The cocoons, torn, but still in position in the lower rooms, left no doubt as to this eccentric mode of exit. The same fact, moreover, was repeated, in several bramble- stumps, in the case of Osmia tridentata; it was likewise repeated in the case of Anthidium scapulare. The observation was worth confirming by experiment.

I select a bramble-stem with the thinnest rind possible, so as to facilitate the Osmiae's work. I split it in half, thus obtaining a smooth-sided trough which will enable me to judge better of future exits. The cocoons are next laid out in one of the troughs. I separate them with disks of sorghum, covering both surfaces of the disk with a generous layer of sealing-wax, a material which the Osmia's mandibles are not able to attack. The two troughs are then placed together and fastened. A little putty does away with the joint and prevents the least ray of light from penetrating. Lastly, the apparatus is hung up perpendicularly, with the cocoons' heads up. We have now only to wait. None of the Osmiae can get out in the usual manner, because each of them is confined between two partitions coated with sealing-wax. There is but one resource left to them if they would emerge into the light of day, that is, for each of them to open a side-window, provided always that they possess the instinct and the power to do so.

In July, the result is as follows: of twenty Osmiae thus immured, six succeed in boring a round hole through the wall and making their way out; the others perish in their cells, without managing to release themselves. But, when I open the cylinder, when I separate the two wooden troughs, I realize that all have attempted to escape through the side, for the wall of each cell bears traces of gnawing concentrated upon one spot. All, therefore, have acted in the same way as their more fortunate sisters; they did not succeed, because their strength failed them. Lastly, in my glass tubes, part-lined with a thick piece of packing-paper, I often see attempts at making a window in the side of the cell: the paper is pierced right through with a round hole.

This then is yet another result which I am glad to record in the history of the bramble-dwellers. When the Osmia, the Anthidium and probably others are unable to emerge through the customary outlet, they take an heroic decision and perforate the side of the shaft. It is the last resource, resolved upon after other methods have been tried in vain. The brave, the strong succeed; the weak perish in the attempt.

Supposing that all the Osmiae possessed the necessary strength of jaw as well as the instinct for this sideward boring, it is clear that egress from each cell through a special window would be much more advantageous than egress through the common door. The Bee could attend to his release as soon as he was hatched, instead of postponing it until after the emancipation of those who come before him; he would thus escape long waits, which too often prove fatal. In point of fact, it is no uncommon thing to find bramble-stalks in which several Osmiae have died in their cells, because the upper storeys were not vacated in time. Yes, there would be a precious advantage in that lateral opening, which would not leave each occupant at the mercy of his environment: many die that would not die. All the Osmiae, when compelled by circumstances, resort to this supreme method; all have the instinct for lateral boring; but very few are able to carry the work through. Only the favourites of fate succeed, those more generously endowed with strength and perseverance.

If the famous law of natural selection, which is said to govern and transform the world, had any sure foundation; if really the fittest removed the less fit from the scene; if the future were to the strongest, to the most industrious, surely the race of Osmiae, which has been perforating bramble-stumps for ages, should by this time have allowed its weaker members, who go on obstinately using the common outlet, to die out and should have replaced them, down to the very last one, by the stalwart drillers of side-openings. There is an opportunity here for immense progress; the insect is on the verge of it and is unable to cross the narrow intervening line. Selection has had ample time to make its choice; and yet, though there be a few successes, the failures exceed them in very large measure. The race of the strong has not abolished the race of the weak: it remains inferior in numbers, as doubtless it has been since all time. The law of natural selection impresses me with the vastness of its scope; but, whenever I try to apply it to actual facts, it leaves me whirling in space, with nothing to help me to interpret realities. It is magnificent in theory, but it is a mere gas-bubble in the face of existing conditions. It is majestic, but sterile. Then where is the answer to the riddle of the world? Who knows? Who will ever know?

Let us waste no more time in this darkness, which idle theorizing will not dispel; let us return to facts, humble facts, the only ground that does not give way under our feet. The Osmia respects her neighbour's cocoon; and her scruples are so great that, after vainly trying to slip between that cocoon and the wall, or else to open a lateral outlet, she lets herself die in her cell rather than effect an egress by forcing her way through the occupied cells. When the cocoon that blocks the way contains a dead instead of a live grub, will the result be the same?

In my glass tubes, I let Osmia-cocoons containing a live grub alternate with Osmia-cocoons in which the grub has been asphyxiated by the fumes of sulphocarbonic acid. As usual, the storeys are separated by disks of sorghum. The anchorites, when hatched, do not hesitate long. Once the partition is pierced, they attack the dead cocoons, go right through them, reducing the dead grub, now dry and shrivelled, to dust, and at last emerge, after wrecking everything in their path. The dead cocoons, therefore, are not spared; they are treated as would be any other obstacle capable of attack by the mandibles. The Osmia looks upon them as a mere barricade to be ruthlessly overturned. How is she apprised that the cocoon, which has undergone no outward change, contains a dead and not a live grub? It is certainly not by sight. Can it be by sense of smell? I am always a little suspicious of that sense of smell of which we do not know the seat and which we introduce on the slightest provocation as a convenient explanation of that which may transcend our explanatory powers.

My next test is made with a string of live cocoons. Of course, I cannot take all these from the same species, for then the experiment would not differ from the one which we have already witnessed; I take them from two different species which leave their bramble-stem at separate periods. Moreover, these cocoons must have nearly the same diameter to allow of their being stacked in a tube without leaving an empty space between them and the wall. The two species adopted are Solenius vagus, which quits the bramble at the end of June, and Osmia detrita, which comes a little earlier, in the first fortnight of the same month. I therefore alternate Osmia-cocoons and Solenius-cocoons, with the latter at the top of the series, either in glass tubes or between two bramble-troughs joined into a cylinder.

The result of this promiscuity is striking. The Osmiae, which mature earlier, emerge; and the Solenius-cocoons, as well as their inhabitants, which by this time have reached the perfect stage, are reduced to shreds, to dust, wherein it is impossible for me to recognize a vestige, save perhaps here and there a head, of the exterminated unfortunates. The Osmia, therefore, has not respected the live cocoons of a foreign species: she has passed out over the bodies of the intervening Solenii. Did I say passed over their bodies? She has passed through them, crunched the laggards between her jaws, treated them as cavalierly as she treats my disks. And yet those barricades were alive. No matter: when her hour came, the Osmia went ahead, destroying everything upon her road. Here, at any rate, is a law on which we can rely: the supreme indifference of the animal to all that does not form part of itself and its race.

And what of the sense of smell, distinguishing the dead from the living? Here, all are alive; and the Bee pierces her way as through a row of corpses. If I am told that the smell of the Solenii may differ from that of the Osmiae, I shall reply that such extreme subtlety in the insect's olfactory apparatus seems to me a rather far-fetched supposition. Then what is my explanation of the two facts? The explanation? I have none to give! I am quite content to know that I do not know, which at least spares me many vain lucubrations. And so I do not know how the Osmia, in the dense darkness of her tunnel, distinguishes between a live cocoon and a dead cocoon of the same species; and I know just as little how she succeeds in recognizing a strange cocoon. Ah, how clearly this confession of ignorance proves that I am behind the times! I am deliberately missing a glorious opportunity of stringing big words together and arriving at nothing.

The bramble-stump is perpendicular, or nearly so; its opening is at the top. This is the rule under natural conditions. My artifices are able to alter that state of things; I can place the tube vertically or horizontally; I can turn its one orifice either up or down; lastly, I can leave the channel open at both ends, which will give two outlets. What will happen under these several conditions? That is what we shall examine with the Three-pronged Osmia.

The tube is hung perpendicularly, but closed at the top and open at the bottom; in fact, it represents a bramble-stump turned upside down. To vary and complicate the experiment, the strings of cocoons are arranged differently in different tubes. In some of them, the heads of the cocoons are turned downwards, towards the opening; in others, they are turned upwards, towards the closed end; in others again, the cocoons alternate in direction, that is to say, they are placed head to head and rear to rear, turn and turn about. I need not say that the separating floors are of sorghum.

The result is identical in all these tubes. If the Osmiae have their heads pointing upwards, they attack the partition above them, as happens under normal conditions; if their heads point downwards, they turn round in their cells and set to work as usual. In short, the general outward trend is towards the top, in whatever position the cocoon be placed.

We here see manifestly at work the influence of gravity, which warns the insect of its reversed position and makes it turn round, even as it would warn us if we ourselves happened to be hanging head downwards. In natural conditions, the insect has but to follow the

Bramble-bees and Others - 4/47

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