One hesitates to touch this horror with the finger-tips. Still, encouraged by my example, seven-year-old Paul, with his tender child’s skin, gathers handfuls of the repulsive insect with no more apprehension than if he were picking a bunch of violets. He fills his boxes with it; he rears it on elm-leaves and handles it daily, for he knows that from this frightful creature he will one day obtain a superb Moth (Chelonia caja, Linn.), clad in scarlet velvet, with the lower wings red and the upper white, sprinkled with brown spots.
What resulted from the child’s familiarity with the shaggy creature? Not even a trace of itching on his delicate skin. I do not speak of mine, which is tanned by the years.
In the osier-beds of our local stream, the [[137]]rushing Aygues, a thorny shrub abounds which, at the advent of autumn, is covered with an infinity of very sour red berries. Its crabbed boughs, which bear but little verdure, are hidden under their clusters of vermilion balls. It is the sallow thorn or sea buckthorn (Hippophaë rhamnoides).
In April, a very hairy but rather pretty caterpillar lives at the expense of this shrub’s budding leaves. He has on his back five dense tufts of hair, set side by side and arranged like the bristles of a brush, tufts deep-black in the centre and white at the edges. He waves two divergent plumes in front of him and sports a third on his crupper, like a feathery tail. These three are black hair-pencils of extreme delicacy.
His greyish Moth, flattened motionless on the bark, stretches his long fore-legs, one against the other, in front of him. You would take them, at a first glance, for antennae of exaggerated proportions. This pose of the extended limbs has won the insect the scientific label of Orgyia, arm’s length; and also the vulgar and more expressive denomination of Patte étendue, or outstretched paw.
Little Paul has not failed, with my aid, to [[138]]rear the pretty bearer of the tufts and brushes. How many times, with his sensitive finger, has he not stroked the creature’s furry costume? He found it softer than velvet. And yet, enlarged under the microscope, the caterpillar’s hairs are horrible barbed spears, no less menacing than those of the Processionary. The resemblance goes no farther: handled without precautions, the tufted caterpillar does not provoke even a simple rash. Nothing could be more harmless than his coat.
It is evident, then, that the cause of the irritation lies elsewhere than in the barbs. If the barbed bristles were enough to poison the fingers, most hairy caterpillars would be dangerous, for nearly all have spiny bristles. We find, on the contrary, that virulence is bestowed upon a very small number, which are not distinguished from the rest by any special structure of the hair.
That the barbs have a part to play, that of fixing the irritant atom upon the epidermis, of keeping it anchored in its place, is, after all, possible; but the shooting pains cannot by any means be caused by the mere prick of so delicate a harpoon.
Much less slender, the hairs clustered [[139]]into pads on the prickly pears are ferociously barbed. Woe to the fingers that handle this kind of velvet too confidently! At the least touch they are pierced with harpoons whose extraction involves a severe tax upon our patience. Other inconvenience there is little or none, for the action of the barb is in this case purely mechanical. Supposing—a very doubtful thing—that the Processionary’s hairs could penetrate our skin, they would act likewise, only with less effect, if they had merely their sharp points and their barbs. What then do they possess in addition?
They must have, not inside them, like the hairs of the nettle, but outside, on the surface, an irritant agent; they must be coated with a poisonous mixture, which makes them act by simple contact.