This change of condition at first suggests oxidation. We must abandon this idea. If the hardening were really the result of oxidization, the grub, being sticky from its birth and always exposed to the air, would long ago have been clad not in a [[259]]delicate coat of adhesive, but in a stiff parchment sheath. Desiccation obviously must take place at the last moment and rapidly, when the grub is preparing to change its shape. Before then, this desiccation would be a danger; now, it is an excellent means of defence.
To ‘fix’ oil-paintings our ingenuity employs siccatives, that is to say, ingredients that act upon the oil, giving it a resinous consistency. The Cionus likewise has its siccative, as the following facts prove. It may be that the grub was labouring to produce this desiccating substance, by some profound change in the process of its organic laboratory, at the time when its poor flesh was quivering with feverish tremors; it may be that it was proceeding to spread the siccative over the whole surface of its body by taking a long walk, the last of its larval life.
7 P.M.—The larva is once more motionless, lying flat on its belly. Is this the end of its preparations? Not yet. The globular structure must have a foundation, a base on which the grub can support itself in order to dilate its ampulla.
8 P.M.—Round the head and the fore-part of the thorax, which, like the rest of the body, are touching the slip of glass, a border of pure white now appears, as though snow had fallen at these points. This forms a sort of horse-shoe enclosing an area in which the snowy deposit is continued in a vague mist. From the base of this border [[260]]some threads of the same white substance radiate in short tufts. This structure denotes work done with the mouth, a miniature wire-drawing. And in fact no such white substance is seen anywhere except around the head. Thus the creature’s two ends take part in the building of the hut: the one in front provides the foundations, the one behind provides the edifice.
10 P.M.—The larva shrinks. With its support, that is to say, its head anchored to the snowy cushion, it brings its hinder end a little nearer; it coils up, hunches its back and gradually turns itself into a ball. Though not yet perceptible, the ampulla is being prepared. The siccative has taken effect; the original gumminess has been transformed into a sort of skin, flexible enough at this moment to be distended by the pressure of the back. When its capacity is large enough, the grub will become unglued, throw off its envelope and find itself at liberty in a spacious enclosure.
I should much like to see this peeling, but things happen so slowly as to drive one to despair. Let us go to bed. What I have seen is enough to enable me to guess the little that remains to be seen.
Next day, when the pale dawn gives me sufficient light, I hasten to my two larvæ. The bladder is completed. It is a graceful ovoid of the finest gold-beater’s-skin, adhering at no point to the insect inside. It has taken some twenty hours to manufacture. [[261]]It has still to be strengthened with a lining. The transparency of the wall enables us to follow the operation.
We see the grub’s little black head rising and falling, swerving this way and that and from time to time gathering with its mandibles, at the door of the intestine, a particle of cement, which is instantly placed in position and meticulously smoothed. So the interior of the hut is plastered, point after point, by small touches. Lest I should not see clearly through the wall, I cut off the top of a bladder, partly uncovering the larva. The work is continued without much hesitation. The strange method is revealed as plainly as one could wish. The grub makes use of its behind as a store of consolidating cement; the end of the intestine serves as the equivalent of the hod from which the bricklayer takes his trowelful of mortar.
This original mode of procedure is familiar to me. At one time, a big Weevil, the Spotted Larinus, inhabiting the blue-headed globe-thistle (Echinops Ritro), enabled me to witness a similar method. The Larinus also expels its own cement. With the tips of its mandibles it gathers it from the evacuating orifice, applying it with strict economy. Moreover it has other materials at its disposal, the hairs and remnants of the florets of its thistle. Its cement is used only to plaster and glaze the work. The Cionus’ larva, on the other hand, employs nothing but the oozings of [[262]]its intestine; consequently the little hut resulting is of incomparable perfection.
Besides the Spotted Larinus, my notes mention other Weevils, for instance, the Garlic-weevil (Brachycerus algirus), whose larvæ possess the art of coating their cells with a thin glaze provided by the rump. This intestinal artifice seems, therefore, to be pretty frequently employed by the Weevils that build little chambers in which the metamorphosis is to take place; but none of them excel in it as does the Cionus. Its task becomes yet more interesting when we consider that, in the same factory, after a very brief interval, three different products are compounded: first a liquid glue, a means of adhesion to the swaying support of the mullein lashed by the winds; then a siccative fluid which transforms the sticky coating into gold-beater’s-skin; and lastly a cement which strengthens the bladder separated from the larva by a sort of moult. What a laboratory, what exquisite chemistry in a scrap of intestine!