I continue therefore to vary the fare, but the results hardly come up to my wishes. The flock refuses my assorted green stuff and even ends by taking a dislike to the elm-leaves. I am beginning to believe that I have failed utterly, when a happy inspiration occurs to me. I have recognized among the bits that go to form the case a few fragments of the mouse-ear hawkweed (Hieracium pilosella). So the [[235]]Psyche frequents that plant. Why should he not browse it? Let us try.
The mouse-ear displays its little round flowers in profusion in a stony field just beside my house, at the foot of the wall where I have so often found Psyche-cases hanging. I gather a handful and distribute it among my different folds. This time the food-problem is solved. The Psyches forthwith settle in solid masses on the hairy leaves and nibble at them greedily in small patches, in which the epidermis of the other surface remains untouched.
We will leave them to their grazing, with which they seem quite satisfied, and ask ourselves a certain question relating to cleanliness. How does the little Psyche get rid of his digestive refuse? Remember that he is enclosed in a sack. One dare not entertain the thought of ordure ejected and accumulating at the far end of the dazzling white plush cap. Filth cannot dwell under so elegant a covering. How is the sordid evacuation managed?
Despite the fact that it ends in a conical point, in which the lens reveals no break of continuity, the sack is not closed at the hinder [[236]]end. Its method of manufacture, by means of a waistband whose fore-edge increases in dimensions in proportion as the rear-edge is pushed farther back, proves this sufficiently. The hinder end becomes pointed simply owing to the shrinking of the material, which contracts of itself at the part where the caterpillar’s decreasing diameter no longer distends it. There is thus at the point a permanent hole whose lips remain closed. The caterpillar has only to go a little way back and the stuff expands, the hole widens, the road is open and the excretions fall to the ground. On the other hand, so soon as the caterpillar takes a step forward into his case, the rubbish-shoot closes of itself. It is a very simple and very ingenious mechanism, as good as anything contrived by our seamstresses to cope with the shortcomings of a boy’s first pair of breeches.
Meanwhile the grub grows and its tunic continues to fit it, is neither too large nor too small, but just the right size. How is this done? If the text-books were to be credited, I might expect to see the caterpillar split his sheath lengthwise when it became too tight and afterwards enlarge it by means of a piece [[237]]woven between the edges of the rent. That is what our tailors do; but it is not the Psyches’ method at all. They know something much better. They keep on working at their coat, which is old at the back, new in front and always a perfect fit for the growing body.
Nothing is easier than to watch the daily progress in size. A few caterpillars have just made themselves a hood of sorghum-pith. The work is perfectly beautiful; it might have been woven out of snow-flakes. I isolate these smartly-dressed ones and give them as weaving-materials some brown scales chosen from the softest parts that I can find in old bark. Between morning and evening, the hood assumes a new appearance: the tip of the cone is still a spotless white, but all the front part is coarse drapery, very different in colouring from the original plush. Next day, the sorghum felt has wholly disappeared and is replaced, from one end of the cone to the other, by a frieze of bark.
I then take away the brown materials and put sorghum-pith in their stead. This time the coarse, dark stuff retreats gradually towards the top of the hood, while the soft, white stuff gains in width, starting from the [[238]]mouth. Before the day is over, the original elegant mitre will be reconstructed entirely.
This alternation can be repeated as often as we please. Indeed, by shortening each period of work, we can easily obtain, with the two sorts of material, composite products, showing alternate light and dark belts.
The Psyche, as you see, in no way follows the methods of our tailors, with their piece taken out and another piece let in. In order to have a coat always to his size, he never ceases working at it. The particles collected are constantly being fixed just at the edge of the sack, so that the new drapery increases progressively in dimensions, keeping pace with the caterpillar’s growth. At the same time the old stuff recedes, is driven back towards the tip of the cone. Here, through its own springiness, it contracts and closes the muff. Any surplus matter disintegrates, falls into shreds and gradually disappears as the insect roams about and knocks against the things which it meets. The case, new at the front and old at the back, is never too tight because it is always being renewed.
After the very hot period of the year, there comes a moment when light wraps are no [[239]]longer seasonable. Autumnal rains threaten, followed by winter frosts. It is time to make ourselves a thick great-coat with a cape of thatch arranged in a series of waterproof tippets. It begins with a great lack of accuracy. Straws of uneven length and bits of dry leaves are fastened, with no attempt at order, behind the neck of the sack, which must still retain its flexibility so as to allow the caterpillar to bend freely in every direction.