The Life of the fly Part 8

In my narrow trough, things take a more tragic turn. When the sheaths are done for, when the caddis worms that are too slow in making off have been eaten up, the Water beetles return to the rockery at the bottom.

Here, sooner or later, there are lamentable happenings. The naked fugitives are discovered and, succulent morsels that they are, are forthwith torn to pieces and devoured. Within twenty-four hours, not one of my band of caddis worms is left alive. In order to continue my studies, I had to lodge the water beetles elsewhere.

Under natural conditions, the caddis worm has its persecutors, the most formidable of whom appears to be the Water beetle. When we consider that, to thwart the brigand's attacks, it has invented the idea of quitting its scabbard with all speed, its tactics are certainly most appropriate; but, in that case, an exceptional condition becomes obligatory, namely, the capacity for recommencing the work. This most unusual gift of recommencing it possesses in a high measure. I am ready to see its origin in the persecutions of the Dytiscus and other pirates.

Necessity is the mother of industry.

Certain caddis worms, of the Sericostoma and Leptocerus species, clothe themselves in grains of sand and do not leave the bed of the stream. On a clear bottom, swept by the current, they walk about from one bank of verdure to the other and do not think of coming to the surface to float and sail in the sunlight. The collectors of sticks and sh.e.l.ls are more highly privileged. They can remain on the level of the water indefinitely, with no other support than their skiff, can rest in unsubmersible flotillas and can even s.h.i.+ft their place by working the rudder.

To what do they owe this privilege? Are we to look upon the bundle of sticks as a sort of raft whose density is less than that of the water?

Can the sh.e.l.ls, which are always empty and able to contain a few bubbles of air in their spiral, he floats? Can the big joists, which break in so ugly a fas.h.i.+on the none too great regularity of the work, serve to buoy up the over-heavy raft? In short, is the caddis worm versed in the laws of equilibrium and does it choose its pieces, now lighter and now heavier as the case may be, so as to const.i.tute a whole that is capable of floating? The following facts are a refutation of any such hydrostatic calculations in the animal.

I remove a number of caddis worms from their sheaths and submit these, as they are, to the test of water. Whether formed wholly of fibrous remnants or of mixed materials, not one of them floats. The scabbards made of sh.e.l.ls go to the bottom with the swiftness of a bit of gravel; the others sink gently. I experiment with the separate materials one by one. No sh.e.l.l remains on the surface, not even among the Planorbes, which a many-whorled spiral ought, one would think, to keep afloat.

The fibrous remnants must be divided into two categories. The first, darkened by time and soaked with moisture, sink to the bottom. These are the most plentiful. The second, considerably fewer in number, of more recent date and less saturated with water, float very well. The general result is immersion, as in the case of the intact scabbards. I may add that the animal, when removed from its tube, is also unable to float.

Then how does the caddis worm manage to remain on the surface without the support of the gra.s.ses, considering that itself and its sheath are both heavier than water? Its secret is soon revealed. I place a few high and dry on a sheet of blotting paper, which will absorb the excess of liquid unfavorable to successful observation. Outside its natural environment, the animal moves about violently and restlessly. With its body half out of the scabbard, this time composed entirely of fibrous matter, it clutches with its feet at the supporting plane. Then, contracting itself, it draws the scabbard towards it, half-raising it and sometimes even making it a.s.sume a vertical position. Even so do the Bulimi move along, lifting their sh.e.l.l as they complete each crawling step.

After a couple of minutes in the free air, I replace the caddis worm in the water. This time, it floats, but like a cylinder with too much weight below. The sheath remains vertical, with its hinder orifice level with the water. Soon, an air bubble escapes from the orifice. Deprived of this buoy, the skiff at once goes down.

The result is the same with the caddis worms in sh.e.l.l casings. At first, they float, straight up on end, and then dip under and sink, faster than the others, after sending out an air bubble or two through the back window.

That is enough: the secret is out. When cased in wood or in sh.e.l.ls, the caddis worms, which are always heavier than water, are able to keep on the surface by means of a temporary air balloon which decreases the density of the whole structure.

This apparatus works in the simplest manner. Consider the rear of the sheath. It is truncated, wide open and supplied with a membranous part.i.tion, the work of the spinneret. A round hole occupies the center of this screen. Beyond it lies the interior of the scabbard, which is smoothly lined and wadded with satin, however rough the exterior may be.

Armed at the stern with two hooks which bite into the silky lining, the animal is able to move backwards and forwards at will inside the cylinder, to fix its grapnels at whatever point it pleases and thus to keep a hold on the cylinder while the six legs and the fore part are outside.

When at rest, the body remains indoors entirely and the grub occupies the whole of the tube. But let it contract ever so little towards the front, or, better still, let it stick out a part of its body: a vacuum is formed behind this sort of piston, which may be compared with that of a pump. Thanks to the rear window, a valve without a plug, this vacuum at once fills, thus renewing the aerated water around the gills, a soft fleece of hairs distributed over the back and belly.

The piston stroke affects only the work of breathing; it does not alter the density, makes hardly any change in that which is heavier than water. To lighten the weight, the caddis worm must first rise to the surface. With this object, it scales the gra.s.ses of one support after the other; it clambers up, sticking to its purpose in spite of the drawback of its f.a.ggot dragging through the tangle. When it has reached the goal, it lifts the rear end a little above the water and gives a stroke of the piston. The vacuum thus obtained fills with air. That is enough: skiff and boatman are in a position to float. The now useless support of the gra.s.ses is abandoned. The time has come for evolutions on the surface, in the glad sunlight.

The caddis worm possesses no great talent as a navigator. To turn round, to tack about, to s.h.i.+ft its place slightly by a backward movement is all that it can do; and even that it does very clumsily. The front part of the body, sticking out of the case, acts as a rudder. Three or four times over, it rises abruptly, bends, comes down again and strikes the water. These paddle strokes, repeated at intervals, carry the unskilled oarsman to fresh lat.i.tudes. It becomes a voyage on the right seas when the crossing measures a hand's breadth.

However, tacking on the surface of the water affords the caddis worm no pleasure. It prefers to twitter in one spot, to remain stationary in flotillas. When the time comes to return to the quiet of the mud bed at the bottom, the animal, having had enough of the sun, draws itself wholly into its sheath again and, with a piston stroke, expels the air from the back room. The normal density is restored and it sinks slowly to the bottom.

We see, therefore, that the caddis worm has not to trouble about hydrostatics when building its scabbard. In spite of the incongruity of its work, in which the bulky and less dense portions seem to balance the more solid, concentrated part, it is not called upon to contrive an equipoise between the light and the heavy. It has other artifices whereby to rise to the surface, to float and to dive down again. The ascent is made by the ladder of the water weeds. The average density of the sheath is of no importance, so long as the burden to be dragged is not beyond the animal's strength. Besides, the weight of the load is greatly reduced when moved in the water.

The admission of a bubble of air into the back chamber, which the animal ceases to occupy, allow it, without further to-do, to remain for an indefinite period on the surface. To dive down again, the caddis worm has only to retreat entirely into its sheath. The air is driven out; and the canoe, resuming its mean density, a greater specific density than that of water, goes under at once and descends of its own accord.

There is, therefore, no choice of materials on the builder's part, no nice calculation of equilibrium, save for one condition, that no stony matter be admitted. That apart, everything serves, large and small, joist and sh.e.l.l, seed and billet. Built up at haphazard, all these things make an impregnable wall. One point alone is essential: the weight of the whole must slightly exceed that of the water displaced; if not, there could be no steadiness at the bottom of the pond, without a perpetual anchorage struggling against the pull of the water. In the same manner, quick submersion would be impossible at times when the surface became dangerous and the frightened creature wanted to leave it.

Nor does this important heavier-than-water question call for lucid discernment, seeing that almost the whole of the sheath is constructed at the bottom of the pond, whither all the materials picked up at random, having descended once before, are likely to descend again. In the sheaths, the parts capable of floating are very rare. Without taking their specific levity into account, simply so as not to remain idle, the caddis worm fixed them to its bundle when sporting on the surface of the water.

We have our submarines, in which hydraulic ingenuity displays its highest resources. The caddis worms have theirs, which emerge, float on the surface, dip down and even stop at mid-depth by releasing gradually their surplus air. And this apparatus, so perfectly balanced, so skilful, requires no knowledge on the part of its constructor. It comes into being of itself, in accordance with the plans of the universal harmony of things.

CHAPTER IX. THE GREENBOTTLES

I have wished for a few things in my life, none of them capable of interfering with the common weal. I have longed to possess a pond, screened from the indiscretion of the pa.s.sers by, close to my house, with clumps of rushes and patches of duckweed. Here, in my leisure hours, in the shade of a willow, I should have meditated upon aquatic life, a primitive life, easier than our own, simpler in its affections and its brutalities. I should have watched the unalloyed happiness of the mollusk, the frolics of the Whirligig, the figure-skating of the Hydrometra [a water bug known as the Pond skater], the dives of the Dytiscus beetle, the veering and tacking of the Notonecta [the water boatman], who, lying on her back, rows with two long oars, while her short forelegs, folded against her chest, wait to grab the coming prey.

I should have studied the eggs of the Planorbis, a glairy nebula wherein focuses of life are condensed even as suns are condensed in the nebulae of the heavens. I should have admired the nascent creature that turns, slowly turns in the orb of its egg and describes a volute, the draft, perhaps, of the future sh.e.l.l. No planet circles round its center of attraction with greater geometrical accuracy.

I should have brought back a few ideas from my frequent visits to the pond. Fate decided otherwise: I was not to have my sheet of water. I have tried the artificial pond, between four panes of gla.s.s. A poor s.h.i.+ft! Our laboratory aquariums are not even equal to the print left in the mud by a mule's hoof, when once a shower has filled the humble basin and life has stocked it with its marvels.

In spring, with the hawthorn in flower and the crickets at their concerts, a second wish often came to me. Along the road, I light upon a dead mole, a snake killed with a stone, victims both of human folly.

The mole was draining the soil and purging it of its vermin. Finding him under his spade, the laborer broke his back for him and flung him over the hedge. The snake, roused from her slumber by the soft warmth of April, was coming into the sun to shed her skin and take on a new one.

Man catches sight of her: 'Ah, would you?' says he. 'See me do something for which the world will thank me!'

And the harmless beast, our auxiliary in the terrible battle which husbandry wages against the insect, has its head smashed in and dies.

The two corpses, already decomposing, have begun to smell. Whoever approaches with eyes that do not see turns away his head and pa.s.ses on. The observer stops and lifts the remains with his foot; he looks. A world is swarming underneath; life is eagerly consuming the dead. Let us replace matters as they were and leave death's artisans to their task.

They are engaged in a most deserving work.

To know the habits of those creatures charged with the disappearance of corpses, to see them busy at their work of disintegration, to follow in detail the process of trans.m.u.tation that makes the ruins of what has lived return apace into life's treasure house: these are things that long haunted my mind. I regretfully left the mole lying in the dust of the road. I had to go, after a glance at the corpse and its harvesters.

It was not the place for philosophizing over a stench. What would people say who pa.s.sed and saw me!

And what will the reader himself say, if I invite him to that sight?

Surely, to busy one's self with those squalid s.e.xtons means soiling one's eyes and mind? Not so, if you please! Within the domain of our restless curiosity, two questions stand out above all others: the question of the beginning and the question of the end. How does matter unite in order to a.s.sume life? How does it separate when returning to inertia? The pond, with its Planorbis eggs turning round and round, would have given us a few data for the first problem; the Mole, going bad under conditions not too repulsive, will tell us something about the second: he will show us the working of the crucible wherein all things are melted to begin anew. A truce to nice delicacy! Odi profanum vulgus et arceo; hence, ye profane: you would not understand the mighty lesson of the rag tank.

I am now in a position to realize my second wish. I have s.p.a.ce, air and quiet in the solitude of the harmas. None will come here to trouble me, to smile or to be shocked at my investigations. So far, so good; but observe the irony of things: now that I am rid of pa.s.sers by, I have to fear my cats, those a.s.siduous prowlers, who, finding my preparations, will not fail to spoil and scatter them. In antic.i.p.ation of their misdeeds, I establish workshops in midair, whither none but genuine corruption agents can come, flying on their wings. At different points in the enclosure, I plant reeds, three by three, which, tied at their free ends, form a stable tripod. From each of these supports, I hang, at a man's height, an earthenware pan filled with fine sand and pierced at the bottom with a hole to allow the water to escape, if it should rain.

I garnish my apparatus with dead bodies. The snake, the lizard, the toad receive the preference, because of their bare skins, which enable me better to follow the first attack and the work of the invaders. I ring the changes with furred and feathered beasts. A few children of the neighborhood, allured by pennies, are my regular purveyors. Throughout the good season, they come running triumphantly to my door, with a snake at the end of a stick, or a lizard in a cabbage leaf. They bring me the rat caught in a trap, the chicken dead of the pip, the mole slain by the gardener, the kitten killed by accident, the rabbit poisoned by some weed. The business proceeds to the mutual satisfaction of sellers and buyer. No such trade had ever been known before in the village nor ever will be again.

April ends; and the pans rapidly fill. An ant, ever so small, is the first arrival. I thought I should keep this intruder off by hanging my apparatus high above the ground: she laughs at my precautions. A few hours after the deposit of the morsel, fresh still and possessing no appreciable smell, up comes the eager picker-up of trifles, scales the stems of the tripod in processions and starts the work of dissection.

If the joint suits her, she even goes to live in the sand of the pan and digs herself temporary platforms in order to work the rich find more at her ease.

All through the season, from start to finish, she will always be the promptest, always the first to discover the dead animal, always the last to beat a retreat when nothing more remains than a heap of little bones bleached by the sun. How does the vagabond, pa.s.sing at a distance, know that, up there, invisible, high on the gibbet, there is something worth going for? The others, the real knackers, wait for the meat to go bad; they are informed by the strength of the effluvia. The ant, gifted with greater powers of scent, hurries up before there is any stench at all.

But, when the meat, now two days old and ripened by the sun, exhales its flavor, soon the master ghouls appear upon the scene: Dermestes [bacon beetles, small flesh-eating beetles] and Saprini [exceedingly small flesh-eating beetles], Silphae [carrion beetles] and Necrophori [burying beetles], flies and Staphylini [rove beetles], who attack the corpse, consume it and reduce it almost to nothing. With the ant alone, who each time carries off a mere atom, the sanitary operation would take too long; with them, it is a quick business, especially as certain of them understand the process of chemical solvents.

These last, who are high cla.s.s scavengers, are ent.i.tled to first mention. They are flies, of many various species. If time permitted, each of those strenuous ones would deserve a special examination; but that would weary the patience of both the reader and the observer. The habits of one will give us a summary notion of the habits of the rest.

We will therefore confine ourselves to the two princ.i.p.al subjects, namely, the Luciliae, or greenbottles, and the Sarcophagae, or grey flesh flies.

The Luciliae--flies that glitter--are magnificent flies known to all of us. Their metallic l.u.s.ter, generally a golden green, rivals that of our finest beetles, the Rosechafers, Buprestes and leaf beetles. It gives one a shock of surprise to see so rich a garb adorn those workers in putrefaction. Three species frequent my pans: Lucilia Caesar, LIN., L.

cadaverina, LIN., and L. cuprea, ROB. The first two, both of whom are gold-green, are plentiful; the third, who sports a coppery l.u.s.ter, is rare. All three have red eyes, set in a silver border.

Lucilia Caesar is larger than L. cadaverina and also more forward in her business. I catch her in labor on the 23rd of April. She has settled in the spinal ca.n.a.l of a neck of mutton and is laying her eggs on the marrow. For more than an hour, motionless in the gloomy cavity, she goes on packing her eggs. I can just see her red eyes and her silvery face.

At last, she comes out. I gather the fruit of her labor, an easy matter, for it all lies on the marrow, which I extract without touching the eggs.

A census would seem important. To take it at once is impracticable: the germs form a compact ma.s.s, which would be difficult to count. The best thing is to rear the family in a jar and to reckon by the pupae buried in the sand. I find a hundred and fifty-seven. This is evidently but a minimum; for Lucilia Caesar and the others, as the observations that follow will tell me, lay in packets at repeated intervals. It is a magnificent family, promising a fabulous legion to come.

The greenbottles, I was saying, break up their laying into sections. The following scene affords a proof of this. A Mole, shrunk by a few days'

evaporation, lies spread upon the sand of the pan. At one point, the edge of the belly is raised and forms a deep arch. Remark that the Greenbottles, like the rest of the flesh eating flies, do not trust their eggs to uncovered surfaces, where the heat of the sun's rays might endanger the existence of the delicate germs. They want dark hiding places. The favorite spot is the lower side of the dead animal, when this is accessible.

In the present case, the only place of access is the fold formed by the edge of the belly. It is here and here alone that this day's mothers are laying. There are eight of them. After exploring the piece and recognizing its good quality, they disappear under the arch, first this one, then that, or else several at a time. They remain under the Mole for a considerable while. Those outside wait, but go repeatedly to the threshold of the cavern to take a look at what is happening within and see whether the earlier ones have finished. These come out at last, perch on the animal and wait in their turn. Others at once take their place in the recesses of the cave. They remain there for some time and then, having done their business, make room for more mothers and come forth into the sunlight. This going in and out continues throughout the morning.

We thus learn that the laying is effected by periodical emissions, broken with intervals of rest. As long as she does not feel ripe eggs coming to her oviduct, the greenbottle remains in the sun, hovering to and fro and sipping modest mouthfuls from the carca.s.s. But, as soon as a fresh stream descends from her ovaries, quick as lightning she makes for a propitious site whereon to deposit her burden. It appears to be the work of several days thus to divide the total laying and to distribute it at different points.

I carefully raise the animal under which these things are happening.

The egg laying mothers do not disturb themselves; they are far too busy.

Their ovipositor extended telescope fas.h.i.+on, they heap egg upon egg.

With the point of their hesitating, groping instrument, they try to lodge each germ, as it comes, farther into the ma.s.s. Around the serious, red-eyed matrons, the Ants circle, intent on pillage. Many of them make off with a greenbottle egg between their teeth. I see some who, greatly daring, effect their theft under the ovipositor itself. The layers do not put themselves out, let the ants have their way, remain impa.s.sive.

They know their womb to be rich enough to make good any such larceny.