The grub was a mighty evacuator in its active period, as is proved by the brown granules which it has scattered in profusion along its road. As the transformation approached, it became more moderate; it began to save up, amassing a hoard of paste of a most fine and binding quality. Observe the tip of its belly as it withdraws from the world. You will see a wide dark patch. This is the bag of cement showing through its skin. This store, so well provided, tells us plainly in what the artisan specializes: [[29]]the Cetonia-larva works exclusively in fæcal masonry.
If proofs were needed, here they are. I isolate some larvæ which have attained their full maturity and are ready to build, in small jars, placing one in each. As building needs a support, I provide each jar with some slight contents, which can easily be removed. One receives some cotton-wool, chopped small with the scissors; another some bits of paper, the size of a lentil; a third some parsley-seed; a fourth some radish-seed. I use whatever comes to hand, without preference for this or that.
The larvæ do not hesitate to bury themselves in these surroundings, which their race has never frequented. There is here no earthy matter, such as we should expect to find used in the construction of the cocoons; there is no clay to be collected. Everything is perfectly clean. If the grub builds, it can only do so with mortar from its own factory. But will it build?
To be sure it will and supremely well. In a few days’ time I have magnificent cocoons, as strong as those that I extracted from the leaf-mould. They are, moreover, much prettier in appearance. In the flask [[30]]containing cotton-wool, they are clad in a fluffy fleece; in that containing bits of paper, they are covered with white tiles, as though they had been snowed upon; in those containing radish or parsley-seed they have the look of nutmegs embellished with an accurate milling. This time the work is really beautiful. When human artifice assists the talent of the stercoral artist, the result is a pretty toy.
The outer wrapper of paper scales, seeds or tufts of cotton-wool adheres fairly well. Beneath it is the real wall, consisting entirely of brown cement. The regularity of the shell gives us at first the idea of an intentional arrangement. The same idea occurs to us if we consider the cocoon of the Golden Cetonia, which is often prettily adorned with a rubble of droppings. It looks as though the grub collected from all around such building-stones as suit its purpose and encrusted them piecemeal in the mortar to give greater strength to the work.
But this is not so at all. There is no mosaic-work. With its round rump the larva presses back the shifting material on every side; it adjusts it, levels it by simple pressure and then fixes it, at one point after another, [[31]]by means of its mortar. Thus it obtains an egg-shaped cavity which it reinforces at leisure with fresh layers of plaster, until its excremental reserves are exhausted. Everything that is reached by the trickling of the cement sets like concrete and henceforth forms part of the wall, without any further intervention by the builder.
To follow the grub through the whole course of its labours is impracticable: it works under a roof, protected from our indiscretion. But we can at least surprise the essential secret of its method. I select a cocoon whose softness indicates that the work is not yet completed. I make a moderate hole in it. If it were too wide, the breach would discourage the occupant and would make it impossible for the grub to repair its shattered roof, not for lack of materials, but for want of support.
Let us make a cautious incision with the point of a penknife and look. The grub is rolled into a hook which is almost closed. Feeling uneasy, it puts its head to the sky-light which I have opened and investigates what has happened. The accident is soon perceived. Thereupon the hook closes entirely, the opposite poles of the grub come [[32]]into mutual contact and then and there the builder is in possession of a pellet of cement which the stercoral factory has that moment furnished. To display such prompt obedience the intestine must certainly be peculiarly obliging. That of the Cetonia-larva is very highly so; directly it is called upon to act, it acts.
Now the true function of the legs is revealed. Of no use for walking, they become precious auxiliaries when the time comes for building. They are tiny hands that seize the piece gathered by the mandibles, turn it over and over, and hold it while the mason subdivides it and applies it economically. The pincers of the mandibles serve as a trowel.
They cut bit after bit from the lump, chewing and kneading the material and then spreading it on the edge of the breach. The forehead presses and smooths it as it is laid. When the supply of the moment is exhausted, the grub, coiling itself again into a closed hook, will obtain a further piece from its warehouse, which remains obedient to its orders.