Natural Wonders

by Edwin Tenney Brewster

But how does a little worm, no bigger round than a slender pin, finding itself in the midst of a great tree, with nothing near it but tough bark which it cannot eat, know in the first place that there are fresh green buds anywhere, and how in the second place, does it find its way to the tips of the twigs where the buds are? The answer is, that it doesn’t. The little caterpillar knows no more about buds and food and the way to them than the tree itself does. It is simply built like a tree, so that when it first leaves its nest, it always turns its head up, and when it has a choice between light and darkness, turns toward the light.

So the caterpillar simply turns up and toward the light, just as a plant would, and with no more intelligence than a plant has, and no more idea what it is about. But of course, crawling up and toward the light, sooner or later brings it to the outer ends of the branches where its food is.

You can easily prove this by putting the young caterpillars in a bottle, or a wide-mouthed jar. If you lay the jar down on the table with the closed end toward the window, every caterpillar will crawl to the closed end, and never a one will crawl back away from the light to the open end and escape. You don’t need any cover; the light holds them fast prisoners. But turn the jar round, open end toward the window, and soon there will not be a caterpillar left in it.

Suppose now, when your caterpillars are at the closed end of the jar toward the window, you take some fresh leaves, from the tree on which you found the insects (since these are presumably the sort they eat) and put them in the open end of the jar away from the window. The little caterpillars will stay where they are till they all starve to death, before one of them will turn round and crawl away from the light toward its dinner. They are even more helpless than a plant, which can at least send its roots toward water, no matter how the light comes.

Also, as I have explained, the caterpillars must crawl up. So they cannot escape from an open jar placed mouth down. Neither can they escape from an open jar placed mouth up; because when they come to the lip of the jar, in order to go farther, they must turn head down to crawl down the outside. But they cannot crawl head down so there they must stay. Moreover, if you put food in the bottom of the jar while they are at the top, they can never crawl down to get it. They cannot turn head down, and they do not have sense enough to crawl backwards.

There is, nevertheless, this difference between caterpillars and plants. If the plant grows up and turns toward the sun at all, it does so always; but the caterpillar changes its nature, and after it has reached the buds and once fed, then the impulse to move upwards and lightward, is no longer useful, and so in a large measure disappears.

Still many sorts of caterpillars keep these willy-nilly turnings, until they are full grown. Our common—our much too common—tent-caterpillar, is accustomed to leave its tent during the warm part of the day, crawl to the tips of the branches where its food is, eat until the cool of the evening begins, and then return to its tent. In no sense, however, does it go after its food, knowing what it wants. During the warm part of the day, it simply becomes like a plant stem, head up, and crawls. It has to head up, and it has to crawl. So in the end it reaches its food, but it doesn’t know anything about how it gets there.

I have often on an early summer afternoon, when the caterpillars are getting restless and just ready to start out, taken the tent, inhabitants and all, and put it on top of a post or a smooth rock. The caterpillars being disturbed, at once start to crawl away. They start in all directions. In a moment, of course, they find themselves crawling head down. That being against the rules, they turn and crawl up again. In no possible way can a single caterpillar get off the top of that rock or post, until the regular time for them to knock off eating and go back to the tent. Then they have to crawl down; and cannot crawl up if they try. So the chief difference between tent-caterpillars and plants, is that while the plant always turns its root down and its stem up, the animal turns its whole body down at certain times of day, and turns its whole body up at certain others. One can hardly say that either has any more sense, or intelligence, or knowledge, than the other.

All caterpillars, while they remain caterpillars, have to crawl toward the light. All caterpillars, also, after they have changed into butterflies and moths, when they fly, have to fly toward the light also. That is why the swarms of moths collect around the arc lights on the streets, fly into lighted rooms thru unscreened windows in the evening, circle about the reading lamp, or if the light chances to be a candle with an uncovered flame, fly into it and are burned.

People will tell you that the moth is curious, wants to see what the light is. But he isn’t; any more than the leaf is curious to look out of the window to see what is going on in the street. Both alike simply turn toward the brightest light. The moth, having turned toward the light, when he flies, flies toward it. If the leaf could fly, it also would fly into the flame and be burned.