The Life of the fly Part 9

Indeed, what escapes the depredations of the ants promises a plenteous brood. Let us come back a few days later and lift the mole again.

Underneath, in a pool of sanies, is a surging ma.s.s of swarming sterns and pointed heads, which emerge, wriggle and dive in again. It suggests a seething billow. It turns one's stomach. It is horrible, most horrible. Let us steel ourselves against the sight: it will be worse elsewhere.

Here is a fat snake. Rolled into a compact whorl, she fills the whole pan. The greenbottles are plentiful. New ones arrive at every moment and, without quarrel or strife, take their place among the others, busily laying. The spiral furrow left by the reptile's curves is the favorite spot. Here alone, in the narrow s.p.a.ce between the folds, are shelters against the heat of the sun. The glistening Flies take their places, side by side, in rows; they strive to push their abdomen and their ovipositor as far forward as possible, at the risk of rumpling their wings and c.o.c.king them towards their heads. The care of the person is neglected amid this serious business. Placidly, with their red eyes turned outwards, they form a continuous cordon. Here and there, at intervals, the rank is broken; layers leave their posts, come and walk about upon the snake, what time their ovaries ripen for another emission, and then hurry back, slip into the rank and resume the flow of germs. Despite these interruptions, the work of breeding goes fast. In the course of one morning, the depths of the spiral furrow are hung with a continuous white bark, the heaped up eggs. They come off in great slabs, free of any stain; they can be shoveled up, as it were, with a paper scoop. It is a propitious moment if we wish to follow the evolution at close quarters. I therefore gather a profusion of this white manna and lodge it in gla.s.s tubes, test tubes and jars, with the necessary provisions.

The eggs, about a millimeter long, are smooth cylinders, rounded at both ends. They hatch within twenty-four hours. The first question that presents itself is this: how do the greenbottle grubs feed? I know quite well what to give them, but I do not in the least see how they manage to consume it. Do they eat, in the strict sense of the word? I have reasons to doubt it.

Let us consider the grub grown to a sufficient size. It is the usual fly larva, the common maggot, shaped like an elongated cone, pointed in front, truncated behind, where two little red spots show, level with the skin: these are the breathing holes. The front, which is called the head by stretching a word--for it is little more than the entrance to an intestine--the front is armed with two little black hooks, which slide in a translucent sheath, project a little way outside and go in turn by turn. Are we to look upon these as mandibles? Not at all, for, instead of having their points facing each other, as would be required in a real mandibular apparatus, the two hooks work in parallel directions and never meet. What they are is ambulatory organs, grapnels a.s.sisting locomotion, which give a purchase on the plane and enable the animal to advance by means of repeated contractions. The maggot walks with the aid of what a superficial examination would p.r.o.nounce to be a machine for eating. It carries in its gullet the equivalent of the climber's alpenstock.

Let us hold it, on a piece of flesh, under the lens. We shall see it walking about, raising and lowering its head and, each time, stabbing the meat with its pair of hooks. When stationary, with its crupper at rest, it explores s.p.a.ce with a continual bending of its fore part; its pointed head pokes about, jabs forward, goes back again, producing and withdrawing its black mechanism. There is a perpetual piston play. Well, look as carefully and conscientiously as I please, I do not once see the weapons of the mouth tackle a particle of flesh that is torn away and swallowed. The hooks come down upon the meat at every moment, but never take a visible mouthful from it. Nevertheless, the grub waxes big and fat. How does this singular consumer, who feeds without eating, set about it? If he does not eat, he must drink; his diet is soup. As meat is a compact substance, which does not liquefy of its own accord, there must, in that case, be a certain recipe to dissolve it into a fluid broth. Let us try to surprise the maggot's secret.

In a gla.s.s tube, sealed at one end, I insert a piece of lean flesh, the size of a walnut, which I have drained of its juices by squeezing it in blotting paper. On the top of this, I place a few slabs of greenbottle eggs collected a moment ago from the snake in my earthen pan. The number of germs is, roughly, two hundred. I close the tube with a cotton plug, stand it upright, in a shady corner of my study, and leave things to take their course. A control tube, prepared like the first, but not stocked with maggots, is placed beside it.

As early as two or three days after the hatching, I obtain a striking result. The meat, which was thoroughly drained by the blotting paper, has become so moist that the young vermin leave a wet mark behind them as they crawl over the gla.s.s. The swarming brood creates a sort of mist with the crossing and criss-crossing of its trails. The control tube, on the contrary, keeps dry, proving that the moisture in which the worms move is not due to a mere exudation from the meat.

Besides, the work of the maggot becomes more and more evident.

Gradually, the flesh flows in every direction like an icicle placed before the fire. Soon, the liquefaction is complete. What we see is no longer meat, but fluid Liebig's extract. If I overturned the tube, not a drop of it would remain.

Let us clear our minds of any idea of solution by putrefaction, for in the second tube a piece of meat of the same kind and size has remained, save for color and smell, what it was at the start. It was a lump and it is a lump, whereas the piece treated by the worms runs like melted b.u.t.ter. Here we have maggot chemistry able to rouse the envy of physiologists when studying the action of the gastric juice.

I obtain better results still with hard-boiled white of egg. When cut into pieces the size of a hazel nut and handed over to the greenbottle's grubs, the coagulated alb.u.men dissolves into a colorless liquid which the eye might mistake for water. The fluidity becomes so great that, for lack of a support, the worms perish by drowning in the broth; they are suffocated by the immersion of their hind part, with its open breathing holes. On a denser liquid, they would have kept at the surface; on this, they cannot.

A control tube, filled in the same way, but not colonized, stands beside that in which the strange liquefaction takes place. The hardboiled white of egg retains its original appearance and consistency. In course of time, it dries up, if it does not turn moldy; and that is all.

The other quaternary compounds performing the same functions as alb.u.men--the gluten of cereals, the fibrin of blood, the casein of cheese and the legumin of chickpeas--undergo a similar modification, in varying degrees. Fed, from the moment of leaving the egg, on any one of these substances, the worms thrive very well, provided that they escape drowning when the gruel becomes too clear; they would not fare better on a corpse. And, as a general rule, there is not much danger of going under: the matter only half liquefies; it becomes a running pea soup, rather than an actual fluid.

Even in this imperfect case, it is obvious that the greenbottle grubs begin by liquefying their food. Incapable of taking solid nourishment, they first transform the spoil into running matter; then, dipping their heads into the product, they drink, they slake their thirst, with long sups. Their dissolvent, comparable in its effects with the gastric juice of the higher animals, is, beyond a doubt, emitted through the mouth.

The piston of the hooks, continually in movement, never ceases spitting it out in infinitesimal doses. Each spot touched receives a grain of some subtle pepsin, which soon suffices to make that spot run in every direction. As digesting, when all is said, merely means liquefying, it is no paradox to a.s.sert that the maggot digests its food before swallowing it.

These experiments with my filthy, evil smelling tubes have given me some delightful moments. The worthy Abbe Spallanzani must have known some such when he saw pieces of raw meat begin to run under the action of the gastric juice which he took, with pellets of sponge, from the stomachs of crows. He discovered the secrets of digestion; he realized in a gla.s.s tube the hitherto unknown labors of gastric chemistry. I, his distant disciple, behold once more, under a most unexpected aspect, what struck the Italian scientist so forcibly. Worms take the place of the crows.

They slaver upon meat, gluten, alb.u.men; and those substances turn to fluid. What our stomach does within its mysterious recesses the maggot achieves outside, in the open air. It first digests and then imbibes.

When we see it plunging into the carrion broth, we even wonder if it cannot feed itself, at least to some extent, in a more direct fas.h.i.+on.

Why should not its skin, which is one of the most delicate, be capable of absorbing? I have seen the egg of the sacred beetle and other dung beetles growing considerably larger--I should like to say, feeding--in the thick atmosphere of the hatching chamber. Nothing tells us that the grub of the greenbottle does not adopt this method of growing. I picture it capable of feeding all over the surface of its body. To the gruel absorbed by the mouth it adds the balance of what is gathered and strained through the skin. This would explain the need for provisions liquefied beforehand.

Let us give one last proof of this preliminary liquefaction. If the carca.s.s--mole, snake or another--left in the open air have a wire gauze cover placed over it, to keep out the flies, the game dries under a hot sun and shrivels up without appreciably wetting the sand on which it lies. Fluids come from it, certainly, for every organized body is a sponge swollen with water; but the liquid discharge is so slow and restricted in quant.i.ty that the heat and the dryness of the air disperse it as it appears, while the underlying sand remains dry, or very nearly so. The carca.s.s becomes a sapless mummy, a mere bit of leather. On the other hand, do not use the wire gauze cover, let the flies do their work unimpeded; and things forthwith a.s.sume another aspect. In three or four days, an oozing sanies appears under the animal and soaks the sand to some distance.

I shall never forget the striking spectacle with which I conclude this chapter. This time, the dish is a magnificent Aesculapius' snake, a yard and a half long and as thick as a wide bottleneck. Because of its size, which exceeds the dimensions of my pan, I roll the reptile in a double spiral, or in two storeys. When the copious joint is in full process of dissolution, the pan becomes a puddle wherein wallow, in countless numbers, the grubs of the greenbottle and those of Sarcophaga carnaria, the Grey or checkered flesh fly, which are even mightier liquefiers. All the sand in the apparatus is saturated, has turned into mud, as though there had been a shower of rain. Through the hole at the bottom, which is protected by a flat pebble, the gruel trickles drop by drop. It is a still at work, a mortuary still, in which the Snake is being drawn off.

Wait a week or two; and the whole will have disappeared, drunk up by the sun: naught but the scales and bones will remain on a sheet of mud.

To conclude: the maggot is a power in this world. To give back to life, with all speed, the remains of that which has lived, it macerates and condenses corpses, distilling them into an essence wherewith the earth, the plant's foster mother, may be nourished and enriched.

CHAPTER X. THE GREY FLESH FLIES

Here the costume changes, not the manner of life. We find the same frequenting of dead bodies, the same capacity for the speedy liquefaction of the fleshy matter. I am speaking of an ash-gray fly, the greenbottle's superior in size, with brown streaks on her back and silver gleams on her abdomen. Note also the blood-red eyes, with the hard look of the knacker in them. The language of science knows her as Sarcophaga, the flesh eater; in the vulgar tongue she is the grey flesh fly, or simply the flesh fly.

Let not these expressions, however accurate, mislead us into believing for a moment that the Sarcophagae are the bold company of master tainters who haunt our dwellings, more particularly in autumn, and plant their vermin in our ill-guarded viands. The author of those offences is Calliphora vomitoria, the bluebottle, who is of a stouter build and arrayed in darkest blue. It is she who buzzes against our windowpanes, who craftily besieges the meat safe and who lies in wait in the darkness for an opportunity to outwit our vigilance. The other, the grey fly, works jointly with the greenbottles, who do not venture inside our houses and who work in the sunlight. Less timid, however, than they, should the outdoor yield be small, she will sometimes come indoors to perpetrate her villainies. When her business is done, she makes off as fast as she can, for she does not feel at home with us.

At this moment, my study, a very modest extension of my open air establishments, has become something of a charnel house. The grey fly pays me a visit. If I lay a piece of butcher's meat on the windowsill, she hastens up, works her will on it and retires. No hiding place escapes her notice among the jars, cups, gla.s.ses and receptacles of every kind with which my shelves are crowded.

With a view to certain experiments, I collected a heap of wasp grubs, asphyxiated in their underground nests. Stealthily she arrives, discovers the fat pile and, hailing as treasure trove this provender whereof her race perhaps has never made use before, entrusts to it an installment of her family. I have left at the bottom of a gla.s.s the best part of a hard-boiled egg from which I have taken a few bits of white intended for the greenbottle maggots. The grey fly takes possession of the remains, recks not of their novelty and colonizes them. Everything suits her that falls within the category of alb.u.minous matters: everything, down to dead silkworms; everything, down to a mess of kidney-beans and chick-peas.

Nevertheless, her preference is for the corpse: furred beast and feathered beast, reptile and fish, indifferently. Together with the greenbottles, she is sedulous in her attendance on my pans. Daily she visits my snakes, takes note of the condition of each of them, savors them with her proboscis, goes away, comes back, takes her time and at last proceeds to business. Still, it is not here, amid the tumult of callers, that I propose to follow her operations. A lump of butcher's meat laid on the window sill, in front of my writing table, will be less offensive to the eye and will facilitate my observations.

Two flies of the genus Sarcophaga frequent my slaughter yard: Sarcophaga carnaria and Sarcophaga haemorrhoidalis, whose abdomen ends in a red speck. The first species, which is a little larger than the second, is more numerous and does the best part of the work in the open air shambles of the pans. It is this fly also who, at intervals and nearly always alone, hastens to the bait exposed on the windowsill.

She comes up suddenly, timidly. Soon she calms herself and no longer thinks of fleeing when I draw near, for the dish suits her. She is surprisingly quick about her work. Twice over--buzz! Buzz!--the tip of her abdomen touches the meat; and the thing is done: a group of vermin wriggles out, releases itself and disperses so nimbly that I have no time to take my lens and count then accurately. As seen by the naked eye, there were a dozen of them. What has become of them? One would think that they had gone into the flesh, at the very spot where they were laid, so quickly have they disappeared. But that dive into a substance of some consistency is impossible to these newborn weaklings.

Where are they? I find them more or less everywhere in the creases of the meat; singly and already groping with their mouths. To collect them in order to number them is not practicable, for I do not want to damage them. Let us be satisfied with the estimate made at a rapid glance: there are a dozen or so, brought into the world in one discharge of almost inappreciable length.

Those live grubs, taking the place of the usual eggs, have long been known. Everybody is aware that the flesh flies bring forth living maggots, instead of laying eggs. They have so much to do and their work is so urgent! To them, the instruments of the transformation of dead matter, a day means a day, a long s.p.a.ce of time which it is all important to utilize. The greenbottle's eggs, though these are of very rapid development, take twenty-four hours to yield their grubs. The flesh flies save all this time. From their matrix, laborers flow straightway and set to work the moment they are born. With these ardent pioneers of sanitation, there is no rest attendant upon the hatching, there is not a minute lost.

The gang, it is true, is not a numerous one; but how often can it not be renewed! Read Reaumur's description of the wonderful procreating machinery boasted by the Flesh flies. It is a spiral ribbon, a velvety scroll whose nap is a sort of fleece of maggots set closely together and each cased in a sheath. The patient biographer counted the host: it numbers, he tells us, nearly twenty thousand. You are seized with stupefaction at this anatomical fact.

How does the gray fly find the time to settle a family of such dimensions, especially in small packets, as she has just done on my window sill? What a number of dead dogs, moles and snakes must she not visit before exhausting her womb! Will she find them? Corpses of much size do not abound to that extent in the country. As everything suits her, she will alight on other remains of minor importance. Should the prize be a rich one, she will return to it tomorrow, the day after and later still, over and over again. In the course of the season, by dint of packets of grubs deposited here, there and everywhere, she will perhaps end by housing her entire brood. But then, if all things prosper, what a glut, for there are several families born during the year! We feel it instinctively: there must be a check to these generative enormities. Let us first consider the grub. It is a st.u.r.dy maggot, easy to distinguish from the greenbottle's by its larger girth and especially by the way in which its body terminates behind. There is here a sudden breaking off, hollowed into a deep cup. At the bottom of this crater are two breathing holes, two stigmata with amber-red tips.

The edge of the cavity is fringed with half a score of pointed, fleshy festoons, which diverge like the spikes of a coronet. The creature can close or open this diadem at will by bringing the denticulations together or by spreading them out wide. This protects the air holes which might otherwise be choked up when the maggot disappears in the sea of broth. Asphyxia would supervene, if the two breathing holes at the back became obstructed. During the immersion, the festooned coronet shuts like a flower closing its petals and the liquid is not admitted to the cavity.

Next follows the emergence. The hind part reappears in the air, but appears alone, just at the level of the fluid. Then the coronet spreads out afresh, the cup gapes and a.s.sumes the aspect of a tiny flower, with the white denticulations for petals and the two bright red dots, the stigmata at the bottom, for stamens. When the grubs, pressed one against the other, with their heads downwards in the fetid soup, make an unbroken shoal, the sight of those breathing cups incessantly opening and closing, with a little clack like a valve, almost makes one forget the horrors of the charnel yard. It suggests a carpet of tiny Sea anemones. The maggot has its beauties after all.

It is obvious, if there be any logic in things, that a grub so well-protected against asphyxiation by drowning must frequent liquid surroundings. One does not encircle one's hindquarters with a coronet for the sole satisfaction of displaying it. With its apparatus of spokes, the Grey Fly's grub informs us of the dangerous nature of its functions: when working upon a corpse, it runs the risk of drowning. How is that? Remember the grubs of the greenbottle, fed on hard-boiled white of egg. The dish suits them; only, by the action of their pepsin, it becomes so fluid that they die submerged. Because of their hinder stigmata, which are actually on the skin and devoid of any defensive machinery, they perish when they find no support apart from the liquid.

The flesh fly's maggots, though incomparable liquefiers, know nothing of this peril, even in a puddle of carrion broth. Their bulky hind part serves as a float and keeps the air holes above the surface. When, for further investigation, they must needs go under completely, the anemone at the back shuts and protects the stigmata. The grubs of the gray fly are endowed with a life buoy because they are first cla.s.s liquefiers, ready to incur the danger of a ducking at any moment.

When high and dry on the sheet of cardboard where I place them to observe them at my ease, they move about actively, with their breathing rose widespread and their stigmata rising and falling as a support. The cardboard is on my table, at three steps from an open window, and lit at this time of day only by the soft light of the sky. Well, the maggots, one and all of them, turn in the opposite direction to the window; they hastily, madly take to flight.

I turn the cardboard round, without touching the runaways. This action makes the creatures face the light again. Forthwith, the troop stops, hesitates, takes a half turn and once more retreats towards the darkness. Before the end of the racecourse is reached, I again turn the cardboard. For the second time, the maggots veer round and retrace their steps. Repeat the experiment as often as I will, each time the squad wheels about in the opposite direction to the window and persists in avoiding the trap of the revolving cardboard.

The track is only a short one: the cardboard measures three hand's breadths in length. Let us give more s.p.a.ce. I settle the grubs on the floor of the room; with a hair pencil, I turn them with their heads pointing towards the lighted aperture. The moment they are free, they turn and run from the light. With all the speed whereof their cripple's shuffle allows, they cover the tiled floor of the study and go and knock their heads against the wall, twelve feet off, skirting it afterwards, some to the right and some to the left. They never feel far enough away from that hateful illuminated opening.

What they are escaping from is evidently the light, for, if I make it dark with a screen, the troop does not change its direction when I turn the cardboard. It then progresses quite readily towards the window; but, when I remove the screen, it turns tail at once.

That a grub destined to live in the darkness, under the shelter of a corpse, should avoid the light is only natural; the strange part is its very perception. The maggot is blind. Its pointed fore part, which we hesitate to call a head, bears absolutely no trace of any optical apparatus; and the same with every other part of the body. There is nothing but one bare, smooth, white skin. And this sightless creature, deprived of any special nervous points served by ocular power, is extremely sensitive to the light. Its whole skin is a sort of retina, incapable of seeing, of course, but able, at any rate, to distinguish between light and darkness. Under the direct rays of a searching sun, the grub's distress could be easily explained. We ourselves; with our coa.r.s.e skin, in comparison with that of the maggot, can distinguish between suns.h.i.+ne and shadow without the help of the eyes. But, in the present case, the problem becomes singularly complicated. The subjects of my experiment receive only the diffused light of the sky, entering my study through an open window; yet this tempered light frightens them out of their senses. They flee the painful apparition; they are bent upon escaping at all costs.

Now what do the fugitives feel? Are they physically hurt by the chemical radiations? Are they exasperated by other radiations, known or unknown?

Light still keeps many a secret hidden from us and perhaps our optical science, by studying the maggot, might become the richer by some valuable information. I would gladly have gone farther into the question, had I possessed the necessary apparatus. But I have not, I never have had and of course I never shall have the resources which are so useful to the seeker. These are reserved for the clever people who care more for lucrative posts than for fair truths. Let us continue, however, within the measure which the poverty of my means permits.

When duly fattened, the grubs of the flesh flies go underground to transform themselves into pupae. The burial is intended, obviously, to give the worm the tranquillity necessary for the metamorphosis. Let us add that another object of the descent is to avoid the importunities of the light. The maggot isolates itself to the best of its power and withdraws from the garish day before contracting into a little keg.

In ordinary conditions, with a loose soil, it goes hardly lower than a hand's breadth down, for provision has to be made for the difficulties of the return to the surface when the insect, now full grown, is impeded by its delicate fly wings. The grub, therefore, deems itself suitably isolated at a moderate depth. Sideways, the layer that s.h.i.+elds it from the light is of indefinite thickness; upwards, it measures about four inches. Behind this screen reigns utter darkness, the buried one's delight. This is capital.

What would happen if, by an artifice, the sideward layer were nowhere thick enough to satisfy the grub? Now, this time, I have the wherewithal to solve the problem, in the shape of a big gla.s.s tube, open at both ends, about three feet long and less than an inch wide. I use it to blow the flame of hydrogen in the little chemistry lessons which I give my children.

I close one end with a cork and fill the tube with fine, dry, sifted sand. On the surface of this long column, suspended perpendicularly in a corner of my study, I install some twenty Sarcophaga grubs, feeding them with meat. A similar preparation is repeated in a wider jar, with a mouth as broad as one's hand. When they are big enough, the grubs in either apparatus will go down to the depth that suits them. There is no more to be done but to leave them to their own devices.

The worms at last bury themselves and harden into pupae. This is the moment to consult the two apparatus. The jar gives me the answer which I should have obtained in the open fields. Four inches down, or thereabouts, the worms have found a quiet lodging, protected above by the layer through which they have pa.s.sed and on every side by the thickness of the vessel's contents. Satisfied with the site, they have stopped there.

It is a very different matter in the tube. The least buried of the pupae are half a yard down. Others are lower still; most of them even have reached the bottom of the tube and are touching the cork stopper, an insuperable barrier. These last, we can see, would have gone yet deeper if the apparatus had allowed them. Not one of the score of grubs has settled at the customary halting place; all have traveled farther down the column, until their strength gave way. In their anxious flight, they have dug deeper and ever deeper.