The troop begins its steadying-work as soon as it comes into contact with its pasturage, the green cabbage-leaf. Here, there, in its immediate neighbourhood, each grub emits from its spinning-glands short cables so slender that it takes an attentive lens to catch a glimpse of them. This is enough to ensure the equilibrium of the almost imponderable atom.
The vegetarian meal now begins. The grub’s length promptly increases from two millimetres to four. Soon, a moult takes place which alters its costume: its skin becomes speckled, on a pale-yellow ground, with a number of black dots intermingled with white bristles. Three or four days of rest are necessary after the fatigue of breaking cover. [[346]]When this is over, the hunger-fit starts that will make a ruin of the cabbage within a few weeks.
What an appetite! What a stomach, working continuously day and night! It is a devouring laboratory, through which the foodstuffs merely pass, transformed at once. I serve up to my caged herd a bunch of leaves picked from among the biggest: two hours later, nothing remains but the thick midribs; and even these are attacked when there is any delay in renewing the victuals. At this rate, a “hundredweight-cabbage,” doled out leaf by leaf, would not last my menagerie a week.
The gluttonous animal, therefore, when it swarms and multiplies, is a scourge. How are we to protect our gardens against it? In the days of Pliny, the great Latin naturalist, a stake was set up in the middle of the cabbage-bed to be preserved; and on this stake was fixed a Horse’s skull bleached in the sun: a Mare’s skull was considered even better. This sort of bogey was supposed to ward off the devouring brood.
My confidence in this preservative is but an indifferent one; my reason for mentioning it [[347]]is that it reminds me of a custom still observed in our own days, at least in my part of the country. Nothing is so long-lived as absurdity. Tradition has retained, in a simplified form, the ancient defensive apparatus of which Pliny speaks. For the Horse’s skull our people have substituted an eggshell on the top of a switch stuck among the cabbages. It is easier to arrange; also, it is quite as useful, that is to say, it has no effect whatever.
Everything, even the nonsensical, is capable of explanation with a little credulity. When I question the peasants, our neighbours, they tell me that the effect of the eggshell is as simple as can be: the Butterflies, attracted by the whiteness, come and lay their eggs on it. Broiled by the sun and lacking all nourishment on that thankless support, the little caterpillars die; and that makes so many fewer.
I insist; I ask them if they have ever seen slabs of eggs or masses of young caterpillars on those white shells.
“Never,” they reply, with one voice.
“Well, then?”
“It was done in the old days and so we go on doing it: that’s all we know; and that’s enough for us.” [[348]]