Part 2

When our first wasp had made its hole deep enough--this took a pretty long time; we found out later that it was about three inches deep--she brought back the first little circular piece of salt crust and carefully put it over the top of the burrow, thus covering it up entirely and making it look as if no hole were there. Then she flew away, out of the little bare room and off into the pickle-weed somewhere. We waited several minutes but she didn't come back, so we turned our eyes to another wasp near by which had its hole only just begun. It was interesting to see how closely like the first wasp this second one worked. Prying and pulling with the jaws, the same fluttering of the wings and humming, the same backing out of the hole and the swift little flight for a foot or two feet away from the hole to drop the pellet of soil.

I tried to point out to Mary that this was the way animals do which work by instinct and not by reason. That all the animals of the same kind do things in the same way, and that they do them without any teaching or imitating or reasoning out. They are born with the knowledge and skill and the impulse to do the things in the particular way they do. But Mary found this very tiresome and let her eyes rove, and it is well she did or we might not have made our great discovery: a really thrilling discovery it was for us, too.

The first wasp had come back! But not empty handed, or rather not empty mouthed, for in her pointed jaws she held a limp measuring-worm about an inch and a quarter long. A measuring-worm or looper is the caterpillar of a certain kind of moth, and it loops or measures when it walks because it has no feet on the middle of the under side of the body as other caterpillars have, and so has to draw its tail pretty nearly up its head to take a step forward. This naturally makes its body rise up in a fold or loop. "See," cried Mary, "the wasp is going to put the measuring-worm into the hole."

That is exactly what happened. How the wasp could tell where the hole was, was surprising, for it had so carefully put the bit of salt crust in place that you couldn't tell the top of the hole from the rest of the crust-covered ground. But our wasp came straight to the right place. Perhaps as a carrier-pigeon comes to its loft from a hundred miles away, or a cat carried away in a bag to a strange place finds its way quickly back home.

Some of the other wasps that we watched later weren't so sure of their holes, though, and other people who have watched digger-wasps in other places have found them showing varying degrees of uncertainty about locating their nests. Mr. and Mrs. Peckham, who have studied the behavior of the various kinds of digger-wasps more than anybody else in this country, have concluded that the wasps "are guided in their movements by their memory of localities. They go from place to place quite readily because they are familiar with the details of the landscape in the district they inhabit. Fair eyesight and a moderately good memory on their part are all that need be assumed in this simple explanation of the problem."

But quite different from this conclusion is that of Fabre, the wonderful French observer of wasps, who experimented on them in regard to this matter of finding and knowing their holes, by carrying them away shut up in a dark box to the center of a village three kilometers from the nesting ground, and releasing them after being kept all night in the dark boxes. These wasps when released in the busy town, certainly a place never visited by them before, immediately mounted vertically to above the roofs and then instantly and energetically flew south, which was the direction of their holes. Nine separate wasps released one at a time did this without a moment's hesitation, and the next day Fabre found them all at work again at their hole-digging. He knew them by two spots of white paint he had put on each one.

"Are the wasps guided by memory when placed by man beyond their bearings and carried to great distances into regions with which they are unacquainted and in unknown directions?" asks Fabre. "By memory so quick that when, having reached a certain height at which they can in some sort take their bearings, they launch themselves with all their power of wing towards that part of the horizon where their nests are? Is it memory which traces their aerial way across regions seen for the first time? Evidently not," emphatically declares Fabre. So there you are. Where doctors (of science) fall out it is not for you or me to decide.

But Mary was growing excited. "See, she has put the worm down and is prying up the top of the hole. She has got it off. She is--"

"Ss-h," say I, for wasps can hear. Or, wait; that's quite dogmatic. Wasps fly away when you talk too loud. That's better. That's not judging wasp doing by what we can do. That is just telling an observed fact.

Mary "ssh"-ed, but she pointed a plump little finger; a finger trembling with excitement. The wasp had gone down into the uncovered hole with the worm. Then she backed out, found the lid, covered up the hole and flew away into the pickle-weed again!

In twenty minutes she came back, with another limp measuring-worm, straight to the covered hole; worm dropped on the ground; lid taken off; worm dragged in; wasp backed out; lid carefully replaced; flight to the distant jungle of pickle-weed again!

O, this was exciting. Mary fairly exploded into exclamations and questions after the wasp was well away. What are the worms for? Are they dead? The second one seemed to wriggle feebly a little on the ground by the nest while the wasp was getting off the lid. Will she bring more? Will she fill the hole full of worms? Now I knew the answers to some of these questions, for I had been in this happy place before, but I wanted Mary to find out, to discover--exquisite and prideful pleasure--for herself. So I remained dumb.

Three more times the wasp brought worms. Three more times went through all the performance. But the last time she didn't come up for a long time; that is, for several minutes, and when she did come, instead of putting the salt crust on the hole, she got a little pellet of soil and dropped it in; and then another, and many others. Sometimes she scraped them in with her front feet, but there weren't many bits of soil close enough for that, for she had carried them all a foot or so away as she brought them out of the hole. She worked very industriously: jumping and running about, making little buzzing leaps and flights, until she had quite filled up the hole with the five dead worms in the bottom.

Then she did the most wonderful thing. With her fore feet she pawed and raked the surface until it was quite smooth, and with her jaws and horny head she pressed down and tamped the fine bits of soil until they were a little below the surface of the salt crust around the hole, and then she brought again the little circular lid or top of salt crust and carefully put it in the little depression on the top of the filled-in burrow, so that it fitted perfectly with the hard uncut salt crust around the hole's edge!

This is true. Does it seem wonderful to you? Why? Because we think that other animals cannot do what would be a very simple thing indeed for us? Our wasp was evidently concealing the whereabouts of her worm-stored burrow. I don't say that she wanted to conceal it; or decided to conceal it; or even intended to conceal it. She was simply, I say, concealing it. That seems quite certain, doesn't it? Well, this action of cutting out and replacing the bit of salt crust over the burrow was about the simplest and most effective way of concealing the hole that could be reasoned out, if we ourselves were to undertake it. The wasp, and all the other wasps of the same kind in our marshes, concealed their holes in the way that our reason would suggest to us as the best way. But I do not say anything about the wasp's mental processes toward getting at this behavior. One thing is pretty sure. Among a score or hundred of us doing this work, there would be pretty sure to be some to do it in a different sort of way from the others. The wasps of the same kind all do it alike. Perhaps that is the chief difference between reason and instinct.

But if our digger-wasp--whose name is Ammophila, the sand-lover--made Mary's and my eyes bulge out by her cleverness, what shall we think of that other Ammophila that Dr. Williston watched on the plains of Kansas, or that other one still which the Peckhams studied in Wisconsin? These other Ammophilas, instead of using their hard heads to tamp down the soil in the hole, hunted about until they found a suitable little stone which, held tightly in the jaws, was used as a tool to pack and smooth the dirt! And the Kansas wasp did another odd thing. Instead of making its hole of the same caliber or width all the way down, the upper half-inch or so was made of greater diameter than the rest of the burrow so that a little circular shelf ran around the inside of the hole half an inch below the top. Now when the clever Kansas wasp closed the burrow each time it went away to hunt for measuring-worms, it did it in a curious way. I quote the exact words of Professor Williston, the observer: "When the excavation had been carried to the required depth"--this is our professional way of saying, when the hole had been dug deep enough--"the wasp, after surveying the premises, flying away, soon returned with a large pebble in its mandibles, which it carefully deposited within the opening; then, standing over the entrance upon her four posterior feet, she rapidly and most amusingly scraped the dust, 'hand over hand' back beneath her till she had filled the hole above the stone to the top. [The stone of course was resting on the little circular shelf half an inch down in the hole.] ... When she had heaped up the dirt to her satisfaction, she again flew away and immediately returned with a smaller pebble, perhaps an eighth of an inch in diameter, and then standing more nearly erect, with the front feet folded beneath her, she pressed down the dust all over and about the opening, smoothing off the surface and accompanying the action with a peculiar rasping sound."

Is this not a creature of wits, this Kansas wasp? And an undaunted worker? For each time she went away to get a nice fat looper, she covered up her hole in this elaborate way, and each time she came back, she had to remove the half-inch of tamped-down soil and the little covering stone resting on the shelf in the hole.

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.

"Now, to deprive the caterpillar of means of escape, and to render it motionless, will the Hymenopteron [that's the wasp] dart its sting into each of the eight rings provided with feet? Especially will it do so when the prey is small and weak? Certainly not: a single stab will suffice if given in a central spot, whence the torpor produced by the venomous droplet can spread gradually with as little delay as possible into the midst of those segments which bear feet. There can be no doubt which to choose for this single inoculation; it must be the fifth or sixth, which separate the two groups of locomotive rings. The point indicated by rational deduction is also the one adopted by instinct. Finally, let us add that the egg of the Ammophila is invariably laid on the paralyzed ring. There, and there alone, can the young larva bite without inducing dangerous contortions; where a needle prick has no effect, the bite of a grub will have none either, and the prey will remain immovable until the nursling has gained strength and can bite farther on without danger."