Part 7

Mary and I are on perfectly frank terms. We are polite, but also inclined to be honest. And Mary is not going to be an unresisting victim of a garrulous old professor. But Mary need not be afraid that I sha'n't know when I am boring her. We have wireless communication, Mary and I. That's one, probably the principal, reason why we are such good companions. No true companionship can possibly persist without wireless and wordless communication.

"All right," I answer, "here goes, Mary. Say when!"

"I forget how many millions of bushels of corn were raised in the state of Illinois last year, but they were very many. And that means thousands and thousands of acres of corn-fields. Now in all these corn-fields there live certain tiny soft-bodied insects called corn-root aphids. Their food is the sap of the growing corn-plants which they suck from the roots. Although each corn-root aphid is only about one-twentieth of an inch long and one-twenty-fifth of an inch wide and has a sucking-beak simply microscopic in size, yet there are so many millions of these little insects all with their microscopic little beaks stuck into the corn-roots and all the time drinking, drinking the sap which is the life-blood of the corn-plants that they do a great deal of injury to the corn-fields of Illinois and cause a great loss in money to the farmers.

"So the wise men have studied the ways and life of these little aphids to see if some way can be devised to keep them in check. The aphids live only two or three weeks, but each one before it dies gives birth to about twelve young aphids. Now this is a very rapid rate of increase. If all the young which are born live their allotted two or three weeks and produce in their turn twelve new aphids, we should have about ten trillion descendants in a year from a single mother aphid. Ten trillion corn-root aphids, tiny as they are, would make a strip or belt ten feet wide and two hundred and thirty miles long!

"Some other kinds of aphids multiply themselves even more rapidly. An English naturalist has figured out that a single-stem mother of the common aphis, or 'greenfly' of the rose, would give origin, at its regular rate of multiplication and provided each individual born lived out its natural life, which is only a few days at best, to over thirty-three quintrillions of rose aphids in a single season, equal in weight to more than a billion and a half of men. Of course such a thing never happens, because so many of the young aphids get eaten by lady-bird beetles and flower-fly larvæ and other enemies before they come to be old enough to produce young.

"However, besides this rapid increase of the corn-root aphids, there is something else that helps them to be so formidable a pest. And this is that they find very good and zealous friends in the millions of little brown ants that also live in the Illinois corn-fields. These swift, strong, brave little ants make their runways and nests all through the corn-fields, and are very devoted helpers of the soft-bodied helpless aphids. For the aphids pay for this help by acting as 'cattle' for the ants.

"This is what Professor Forbes, a very careful and a very honest naturalist, found out about the ants and the aphids. The eggs of the aphids, hosts of shining black, round, little seed-like eggs, are laid late in the autumn. These eggs are gathered by the ants and heaped up in piles in the galleries of their nests, or sometimes in special chambers made by widening the runways here and there. All through the winter these eggs are cared for by the ants, being carried down into the deeper and warmer chambers in the coldest weather, and brought up nearer the surface when it is warm. When the sunny days of spring begin to come, the eggs are even brought up above ground and scattered about in the sunshine, then carried down again at night. The little ants may be seen sometimes turning the eggs over and over and carefully licking them as if to clean them of dust-particles.

"In the late spring the aphid eggs hatch, and the young must have sap to drink right away. Their little beaks are thirsty for the plant-juices that are their only food. But there are no tender corn-roots ready for them in the fields because the corn has not yet been planted. What, then, shall the hungering baby aphids and their foster-mothers, the little brown ants, do?

"This is what happens. Although it is too early yet for the corn to be growing, there are various kinds of weeds that begin to sprout with the coming on of spring, and two of these, especially, the smart-weed and the pigeon-grass, abundant and wide-spread in all the Mississippi Valley, are sure to be growing in the fields. While the aphids much prefer corn-roots to live on, they will get along very well on the roots of smart-weed or pigeon-grass. So the clever little brown ants put the almost helpless baby aphids on the tender roots of these weeds, and there their tiny beaks begin to be satisfied. Don't you call that clever, Mary?"

"Clever! Gracious!" says Mary. "Do you know Professor Forbes? Is he really--does he always tell the--"

I interrupt. I am sensitive about such questions. I answer rather sharply. "Yes, I _do_ know him; and yes, he always tells the truth. Don't interrupt any more, please, for there is still more of the story." Mary is silent.

"Well, the aphids stay on the smart-weed roots until the corn is planted, which is in about ten days, and the kernels begin to germinate and to send down the tender juice-filled roots. And then the little brown ants take the aphids, now getting larger and stronger, of course, but still too helpless or stupid to do much for themselves except to suck sap, and carry them from the smart-weed roots to the corn-roots--What's that, Mary?"

But Mary had said nothing; just drawn in her breath with a little sound. Still I think it best to remind her that I _do_ know Professor Forbes and that he really _does_ always tell the truth. In fact, I quote to Mary this honest professor's exact words about this transfer of the aphids from the weed-roots to the corn-roots. This is what he writes in his intensely interesting account of the whole life of these little insects: "In many cases in the field, we have found the young root aphis on sprouting weeds (especially pigeon-grass) which have been sought out by the ants before the leaves had shown above the ground; and, similarly, when the field is planted to corn, these ardent explorers will frequently discover the sprouting kernel in the earth, and mine along the starting stem and place the plant aphids upon it."

"And the little brown ants do all this so as to get honey-dew from the aphids?" asks Mary.

"Exactly," I reply. "The ants take such good care of the aphids not because they pity their helplessness or just want to be good, but because they know, by some instinct or reason, that these are the insects that, when they grow up, make honey-dew, which is the kind of food that ants seem to like better than any other. Indeed not only the little brown ants alone take care of the corn-root aphids to get honey-dew, but at least six other kinds of ants that live in the Illinois corn-fields do it. But the little brown ants are the most abundant and seem to give the aphids the best care."

"It is exactly like keeping cows, isn't it," says Mary. "But they don't have to milk them."

"Well," I reply, "I don't know what you would call it, but some other ants that take care of some other kinds of honey-dew insects seem to have to carry on a sort of milking performance to make them pour out their sweet liquid. The ants have to pat or rub them with their hairy little feelers; sort of tickle them to get them to squeeze out a little drop of honey-dew. The truth is, Mary, if I should tell you the really amazing things that ants do, you simply wouldn't believe me at all. But the next time we go out, I'll take you to see for yourself an ant community right on the campus that does some remarkable things. I'd much rather have you see the things yourself than tell you about them."

"I'd rather, too," says Mary, which isn't exactly the nicest thing she could say, but I know what she means. It's that seeing is better than being told by anybody.

And then the up-and-down "ding, dang, dong, ding," of the clock-bells begins its little song in four verses that means the end of an hour. And then come the six slow deep calls of the biggest bell that tell what hour it is. It is the hour for us to go home.

AN HOUR OF LIVING; OR, THE DANCE OF DEATH

"But why didn't he go back if he liked France so much better; and if he had plenty of money?" asked Mary.

"Ah, well, even having plenty of money doesn't always make it possible to do just what we prefer," I say. "The truth is,--if it is the truth, and not just malicious gossip,--it was exactly because he had plenty of money that he couldn't go back. He is supposed to have got that money in some wrong way. Anyway, he didn't seem to care to go back to _la belle France_, but preferred to live solitarily here, and to plant lines of trees and lay out little lakes and build rockwork towers and make terraces and driveways and paths, all in very formal lines, as in the parks at Versailles and St. Cloud, which were the playgrounds of French kings and the pride of all France."

Mary and I were seated on a curious little cement-and-stone imitation tower-ruin that stuck up out of Frenchman's Pond, which is near the campus, and is a good place for seeing things and getting away from the classroom bells. A long row of scraggly Lombardy poplars stretches away from the pond along an old terraced roadway with a cave opening on it. Around two sides of the little lake is a rockwork wall, and across one end, where the pond narrows, is a picturesque stone bridge of single span. Everything is neglected, and altogether Frenchman's Pond and its surroundings are a good imitation of something old and foreign in this glaringly new and extremely Californian bit of the world. It is a favorite place for us to come when I want to tell Mary stories of the castles on the Rhine. We get a proper atmosphere.

It was so sunny and warm this morning that we had given up chatting and were simply sitting or sprawling as comfortably as we could on the irregular top of our _Aussichtsthurm_. A few flying dragons, some in bronze-red mail, some in greenish blue, were wheeling about over the pond, and a meadow-lark kept up a most cheerful singing in the pasture nearby. It was really just the sort of day and place and feeling that Mary and I like best. We knew we ought, as persevering Nature students, to get down and poke around in the weeds and ooze of the edges of the pond so as to see things. But we didn't want to do it, and so we didn't. That is one perfectly beautiful thing about the way Mary and I study Nature. We don't when we don't want to.

But if we didn't climb down to the live things this day at Frenchman's Pond, they came up to us. One of the flying dragons actually swooped so close to our heads that we could hear its shining brittle wings crackle, and only a few minutes after, a curious delicate little creature with four gauzy wings, a pair of projecting eyes with a fixed stare, and three long hair-like tails on its body, lit on Mary's hand and walked slowly and rather totteringly up her bare wrist and fore arm. Then without any fluttering or struggling, it slowly fell over on one side and lay quite still. It was dead!

This rather took our breath away. We are only too well accustomed, unfortunately, to seeing death come to our little companions; they do not live long, at best, and then so many of them get killed and eaten. But they usually make some protest when Death approaches. They do not surrender their brief joy of living in such utterly unresisting way as this little creature did. But when I had got my spectacles properly adjusted, I saw what it was that had died so quietly and suddenly. The little gauzy-winged creature was a May-fly, or ephemera, and life with the May-flies is such a truly ephemeral thing, and death comes regularly so soon and so swiftly, and without any apparent illness or injury intervening between health and dissolution, that we naturalists have ceased to wonder at it. Although this is not because we understand it at all. Far from it. Indeed the death of any creature, except from obvious accident or wasting illness, is one of the mysteries of life. Which sounds rather Irish, but is just what I mean.

But Mary was looking thoughtfully at this dead little May-fly in her hand. It was so soft and delicate of body, had such frail and filmy wings, that it seemed that it must have been very ill-fitted to cope with the hard conditions of insect living, to escape the numerous insect-feeding creatures and to find food and shelter for itself, to be successful, in a word, in the "struggle for existence"! And in a way, this is quite true. But, in another way, it is not true. For the May-flies, in their flying stage, make up for their frailness and feebleness, their inability to feed--they have really no mouth-parts and do not eat at all in their few hours or days of flying life--by existing in enormous numbers, and millions may be killed, or may die from very feebleness, and yet there are enough left to lay the eggs necessary for a new generation, and that is success in life for them. Nothing else is necessary; their whole aim and achievement in life seems to be to lay eggs and start a new generation of May-flies.

I settled back into a still more comfortable position and said: "Did I ever tell you, Mary, of the May-flies' dance of death I saw in Lucerne once, not far from the old bridge across the Reuss with its famous pictures of our own dance of death? Well, then, we'll just about have time before the tower-clock calls us home. Do you want to hear about it?"

"Yes, please," said Mary.

"Well, I had been studying in a great university in an old German town all the spring and early summer and had come to Switzerland for my vacation. You know there are splendid mountains there--"

"The Alps," interrupted Mary. "The highest is Mt. Blanc, 15,730 feet above the sea."

How Mary does know her geography!

"And beautiful lakes," I continue. "And the roads are good for tramping, and the hotels cheap. Anyway, the ones the students go to. I had come to Lucerne from Zurich--"

"Noted for its silks and university where women can go," Mary broke in again.

Bless me, what's the use of going to Europe anyway, if you learn everything about everywhere in the grades?

"And had gone straight to the _Mühlenbrücke_," I go on,--"that's the old bridge all covered with a roof that crosses the Reuss only a few rods from where it flows out of the lake; the lake of Lucerne, you know."

"Of course," said Mary.

"For it is on the ceiling of that bridge," I persist, "that these curious old Dance of Death pictures are painted, and I had heard a great deal about them. They show how everybody is dancing through life to his grave. Not very pleasant pictures, Mary."

"Very unpleasant, I should think," says Mary, positively. "I hope you didn't look at them long."

"No, because, for one reason, it was getting too dark to see them. The sun had set behind the Gutsch--that's a pretty hill just west of Lucerne--and the electric lights were already flashing along the lake-shore promenade. You know what a wonderfully beautiful lake Lucerne is, of course, Mary?"

"Yes; it is unsurpassed in Switzerland, perhaps in Europe, for magnificence of scenery," replies Mary, in level voice.

I resolve to cut geographic information out of any further stories I tell Mary. Do they commit Baedeker to memory nowadays in the schools?

"Exactly," I manage to reply without betraying too much astonishment at this revelation of the American educational method.

"Well, along the shore of this unsurpassed lake at the town of Lucerne there is a broad promenade with trees and benches and electric lights. Behind it are the big hotels all in a curving row, and after dinner all the people come out and stroll about while the band plays. It is a fine sight."

Mary seemed to be getting a little less than interested. She squirmed into a new position on the rough rockwork and then, looking out over the little pond with its hawking dragons whizzing back and forth, she asked: "What about the May-flies, please?"

I really believe she knew all about the hotels and promenade and the band. What wonderful schools!

"I was coming--I have just come to them," I reply with dignity.

I am a professor and have a certain stock supply of dignity to draw on when necessary. It isn't often necessary with Mary.

"Well, as I came from the covered _Mühlenbrücke_ and out on to the lake-shore promenade, I saw a little crowd of people gathered under and about a brilliant arclight hanging in an open place in front of the great Schweizerhof Hotel. The light seemed to me curiously hazy, and even before I got near the crowd I had made a guess at what was going on. My guess that it was a May-fly dance of death was quite right. Perhaps it would really be better to call it a 'dance of life,' for it really was sort of a great wedding dance. But it was a dance of death, too, for the dancers were falling dead or dying out of the dizzying whirly circles by thousands. How many hundreds or thousands or millions of May-flies there were in the dense circling cloud about the light, I have no idea. But the air for twenty feet every way from the light was full of them, and the ground for a circle of thirty or forty feet underneath was not merely covered with the delicate dead creatures, but was covered for from one to two inches deep!

"The crowd of promenaders looked on in gaping wonder. Not one seemed to know what kind of creature this was, nor of course anything about what was really going on; that this was all of the few hours of feverish life which these May-flies enjoyed in their winged state, and that they gave it all up to the business of mating and egg-laying; where they came from, how they had lived before, why they should be here to-night and no other in the whole year, all these things which it seems to me the onlookers ought to have wanted to know, nobody seemed to know, nor anybody seemed particularly to care to.

"But there are places in the world where the people do want to know these things, and a great many more, about the May-flies. One such place is the Thousand Islands in the St. Lawrence River. One day I was sailing down this river among the Thousand Islands, and the acquaintanceship of a small and unusually delicate kind of May-fly was forced on me by the hundreds of them that persisted in alighting on my clothes, my hat, and my hair. They kept walking unsteadily about over my face and hands and the open pages of the book I was trying to read. And they kept dying, dying, all around. One would light on the outer edge of the page, and before it had walked across to the beginning of a sentence, it would die and its body would slide gently down into the back of the book and--be a bookmarker!"

"That's not a very nice way to talk about the poor little dead May-flies," said Mary, rather seriously.

"It isn't, Mary, I know," said I. "But we've got to relieve the gloom of this tale someway, don't you think? There is too much wholesale death in it to suit my publisher! And so I am trying to introduce a little jocularity into it, don't you see, Mary?"

"People are not supposed to be very funny at funerals," said Mary, severely. "Where did the little Thousand Islands May-flies come from, and why do the people there want to know about them?"

"Because there are so many May-flies that they are a great pest. Not by eating crops--for there aren't any, I suppose, and the May-flies don't eat anything anyway--nor by carrying malaria, but just by living and dying all over; everywhere in one's summer cottage, down on the river-bank where you are watching the sunset, under the trees when you are lying in your hammock and trying to read, in your rowboat when you are paddling about to visit your neighbors on other islands. To be walked on and died on by hundreds and hundreds of little flies, and all the time, grows to be very uncomfortable. So the May-flies or river-flies or lake-flies as they are variously called are cordially hated by all the Thousand-Islanders and the St. Lawrence-Riverers. And the people want to know about where they come from, and how they live, and all about them, indeed, so as to try to find some way to be rid of them."

"And do you know where they come from, and how they live, and all about them," asks Mary, with a slightly roguish manner, I fear.

"Well, I know something. In the first place, after the dance of death, the few that don't die fly out over the lake or river or pond and drop a lot of little eggs into it. Then they die happy--if May-flies can be happy. Mind you, I don't say they can. We are the only animals that we know can be happy. And we mostly aren't. From the eggs hatch young May-flies without wings or long thread-like tails, but just little, flat, under-water creatures with gills along the sides so they can breathe without coming up to the surface. Some kinds burrow into the mud at the bottom, some kinds make little tubes or cases in which to live, while others stay mostly on the under side of stones. They eat little water-plants or broken-up stuff they find in the water, although some eat other little live animals, even other young May-flies. And many of them get eaten themselves. They are favorite food of the under-water dragons. You remember, don't you, Mary, how our dragons of Lagunita would snap up the young May-flies in Monday Pond?

"Well, these young May-flies--the ones that don't get eaten by dragons, stone-flies, water-tigers, and other May-flies--grow larger slowly, and wing-pads begin to grow on their backs. In a year, maybe, or two years for some kinds, they are ready for their great change. And this comes very suddenly. Some late afternoon or early evening thousands of young May-flies of the same kind, living in the same lake or river, swim up to the surface of the water, and, after resting there a few moments, suddenly split their skin along the back of the head and perhaps a little way farther along the back, and like a flash squirm out of this old skin, spread out their gauzy wings and fly away. They do this so quickly that your eye can hardly follow the performance."

"And then they all fly to the light and begin their dance of death," breaks in Mary.

"No, wait; they are not yet quite ready for that. First, they do a very unusual thing; something that no other kinds of insects have ever been seen to do. This is it: They fly away to a plant or bush or tree at the water's edge, and there they cling for a little while and then cast their skin again."

"The new skin they have just got, with the wings and everything?" asks Mary.

"Exactly; the new skin. It comes off of the wings, off of the long tails and the short feelers, and all the rest of the body. No other kind of insect but the May-fly casts its skin once its wings are outspread. But now the May-fly is ready for its dizzy dance. And as it has only a few hours to do it in, it usually starts as soon as there are any lights to dance about. Think of it, to come up from under the water, get your wings and be a real May-fly, not just a crawling thing on the bottom of a pond, and have only one evening to live in! Probably to dance the whole evening through is about the best thing to do under such circumstances."

"Don't any of the poor May-flies live for more than one evening?" asks Mary. "It does seem a shame to put in so long a time, one year, two years for some, getting ready to fly and then have only one evening or night for flying."