Insect Stories

by Vernon L. Kellogg

The Peckhams, too, saw an Ammophila in Wisconsin use a pebble as a tool, and what is especially interesting and important, this wasp was only a single individual of several others watched by the observers, all these wasps being of one kind, that is, belonging to the same species. The tool-user thus revealed an individuality that made its actions seem to be dictated by something else than rigid instinct; certainly so if instinct is to be defined as untaught and unreasoned behavior common to all the individuals of a kind. In fact the Peckhams (most persistent, practised and intelligent observers) insist that "in all the processes of Ammophila the character of the work differs with the individual."

But where is Mary in all this digression of mine? Never fear for Mary. While I was mumbling about instinct and reason and automatism and individual idiosyncrasy, Mary was crawling slowly and cautiously about over the salt-crust floor of our room, counting the wasp holes in course of making, and she was making a second discovery. The measuring-worms, limp and lifeless as they appeared, were really not dead! She had seen at least two, left lying on the ground by the hole while the wasp prized off the cover, give feeble wriggles, and one that she poked with a pin squirmed rather energetically. That is, it did if she poked it at one end, but not if she poked it in the middle, which is such a great discovery that it really gets to be science!

Now as one is entitled to take violent measures for the sake of science, Mary and I decided after considerable serious discussion to "collect" the hole which our wasp had finished and apparently left for good. So we dug it up, and on the spot we examined it and all of its insides. And we found it quite true that the loopers were not dead, but they were paralyzed! When we poked a head or tail, each worm could squirm just a little, but if we touched them in the middle, they didn't know it, and on one of them, the top one, we found a little shining white speck.

Mary's excitement became merged into an intense thoughtfulness. Then she cried aloud with eyes shining: "My, it's the egg! the egg of the wasp! and the worms are for food for the young wasp when it hatches!"

Ah, Mary, you have wits! Have you ever heard any one tell about this? Did you really guess it, or not guess it, but actually reason it out for yourself? Mary, I have great hopes of you.

For it is quite true what Mary says. The little white seed-like thing glued on to the last looper's body is the egg of the wasp, and the stung and paralyzed but not killed measuring-worms are the food stored up by this extremely clever narrow-waisted mother for the wingless, footless, blind, almost helpless wasp grub, when it shall hatch from the egg. Down in the darkness of the cell, there will be a horrible tragedy. For days and weeks together the wasp grub will nibble away on the helpless loopers until all five are eaten alive! Then the grub will change to a winged wasp with strong sharp jaws with which she will dig her way up and out of the noisome prison and into the free air and sunlight of the marsh room. And she will then dig holes of her own, find and sting and store loopers, lay an egg on one, and close up the hole just as her mother did. Or at least all this would happen if we hadn't collected the hole. But it will happen in the other holes.

But why should the loopers be only paralyzed instead of killed? Isn't it plain that if killed they would only be decaying carrion by the time the wasp grub was ready to eat them, and young wasps must have fresh meat, not dead and decayed flesh. And if the loopers were simply put in alive, not paralyzed, wouldn't their violent squirming in the hole surely crush the delicate egg or the more delicate newly hatched wasp grub? Or wouldn't they simply dig their way with their heavy jaws out of the hole and away? Or, indeed, could the slender-bodied mother wasp carry and handle successfully a strong squirming looper over an inch long? The reason for the paralyzing of the worms is plain then. But how is this extraordinary condition brought about? And the answer to this, which Mary and I didn't discover for ourselves, but had to find out from the accounts of the men who did, like Fabre and others, reveals the most extraordinary thing that our wasps do. Most people think the wasps that live in communities or large families in big paper nests (the yellow-jackets and hornets) are the most interesting and most intelligent or clever of the wasps. But Mary and I do not think so. The solitary wasps do the most wonderful things, and of all they do, the paralyzing of the insects they store up as food for their young is the hardest to explain on any basis except that of wasp reasoning. But of course we don't have to explain it, which is fortunate for the high record of truth we are trying to establish in this book.

Fabre, the patient Frenchman, waited for years and years for a chance to see just how the Ammophila paralyzes her victims, and at last he saw and understood it. To understand the matter from Fabre's account of it, we must remember that the measuring-worm's body is made up of a series of rings or body segments, in each of which (except the very last) is a little nerve center or brain situated just under the skin on the under side of the body. And all this row of brains is connected by a slender nerve cord running along the middle line of the under side of the long body. Now Fabre saw that the wasp darted its sting into each looper, "once for all at the fifth or sixth segment of the victim." And when he pricked the stung worms with a needle in various parts of the body, he found, just as Mary did, that the needle could entirely pierce the middle of the body (which is where the fifth and sixth segments are), without causing any movement of the worm. "But prick even slightly a segment in front or behind and the caterpillar struggles with a violence proportioned to the distance from the poisoned segment."

Now what is the reason, asks Fabre, for the wasp's selecting this particular spot for stinging the worm, and he answers his own question as follows:

"The loopers have the following organization, counting the head as the first segment: Three pairs of true feet on rings two, three, and four; four pairs of membranous feet on rings seven, eight, nine, and ten, and a last similar pair set on the thirteenth and final ring; in all eight pairs of feet, the first seven making two marked groups—one of three, the other of four pairs. These two groups are divided by two segments without feet, which are the fifth and sixth.