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قراءة كتاب Bramble-Bees and Others
تنويه: تعرض هنا نبذة من اول ١٠ صفحات فقط من الكتاب الالكتروني، لقراءة الكتاب كاملا اضغط على الزر “اشتر الآن"
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 counsels of gravity, which tells it to dig upwards, and it will infallibly reach the exit-door situated at the upper end. But, in my apparatus, these same counsels betray it: it goes towards the top, where there is no outlet. Thus misled by my artifices, the Osmiae perish, heaped up on the higher floors and buried in the ruins.
It nevertheless happens that attempts are made to clear a road downwards. But it is rare for the work to lead to anything in this direction, especially in the case of the middle or upper cells. The insect is little inclined for this progress, the opposite to that to which it is accustomed; besides, a serious difficulty arises in the course of this reversed boring. As the Bee flings the excavated materials behind her, these fall back of their own weight under her mandibles; the clearance has to be begun anew. Exhausted by