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, glasses 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 glass 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 albuminous 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 space 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 sturdy 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 assumes 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 class 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 space. 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 coarse skin, in comparison with

that of the maggot, can distinguish between sunshine 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 shields 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 glass

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 passed 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.



What were they flying from? The light. Above them, the column

traversed forms a more than sufficient shelter; but, at the sides,

the irksome sensation is still felt through a coat of earth half an

inch thick if the descent is made perpendicularly. To escape the

disturbing impression, the grub therefore goes deeper and deeper,

hoping to obtain lower down the rest which is denied it above. It

only ceases to move when worn out with the effort or stopped by an

obstacle.



Now, in a soft diffused light, what can be the radiations capable

of acting upon this lover of darkness? They are certainly not the

simple luminous rays, for a screen of fine, heaped up earth, nearly

half an inch in thickness, is perfectly opaque. Then, to alarm the

grub, to warn it of the over proximity of the exterior and send it

to mad depths in search of isolation, other radiations, known or

unknown, must be required, radiations capable of penetrating a

screen against which ordinary radiations are powerless. Who knows

what vistas the natural philosophy of the maggot might open out to

us? For lack of apparatus, I confine myself to suspicions.



To go underground to a yard's depth--and farther if my tube had

allowed it--is on the part of the Flesh fly's grub a vagary

provoked by unkind experiment: never would it bury itself so low

down, if left to its own wisdom. A hand's breadth thickness is

quite enough, is even a great deal when, after completing the

transformation, it has to climb back to the surface, a laborious

operation absolutely resembling the task of an entombed well

sinker. It will have to fight against the sand that slips and

gradually fills up the small amount of empty space obtained; it

will perhaps, without crowbar or pickaxe, have to cut itself a

gallery through something tantamount to tufa, that is to say,

through earth which a shower has rendered compact. For the

descent, the grub has its fangs; for the assent, the fly has

nothing. Only that moment come into existence, she is a weakling,

with tissues still devoid of any firmness. How does she manage to

get out? We shall know by watching a few pupae placed at the

bottom of a test-tube filled with earth. The method of the Flesh

flies will teach us that of the greenbottles and the other Flies,

all of whom make use of the same means.



Enclosed in her pupa, the nascent fly begins by bursting the lid of

her casket with a hernia which comes between her two eyes and

doubles or trebles the size of her head. This cephalic blister

throbs: it swells and subsides by turns, owing to the alternate

flux and reflux of the blood. It is like the piston of an

hydraulic press opening and forcing back the front part of the keg.



The head makes its appearance. The hydrocephalous monster

continues the play of her forehead, while herself remaining

stationary. Inside the pupa, a delicate work is being performed:

the casting of the white nymphal tunic. All through this

operation, the hernia is still projecting. The head is not the

head of a fly, but a queer, enormous mitre, spreading at the base

into two red skull caps, which are the eyes. To split her cranium

in the middle, shunt the two halves to the right and left and send

surging through the gap a tumor which staves the barrel with its

pressure: this constitutes the Fly's eccentric method.



For what reason does the hernia, once the keg is staved, continue

swollen and projecting? I take it to be a waste pocket into which

the insect momentarily forces back its reserves of blood in order

to diminish the bulk of the body to that extent and to extract it

more easily from the nymphal slough and afterwards from the narrow

channel of the shell. As long as the operation of the release

lasts, it pushes outside all that it is able to inject of its

accumulated humors; it makes itself small inside the pupa and

swells into a bloated deformity without. Two hours and more are

spent in this laborious stripping.



At last, the fly comes into view. The wings, mere scanty stumps,

hardly reach the middle of the abdomen. On the outer edge, they

have a deep notch similar to the waist of a violin. This

diminishes by just so much the surface and the length, an excellent

device for decreasing the friction along the earthy column which

has next to be scaled. The hydrocephalous one resumes her

performance more vigorously than ever; she inflates and deflates

her frontal knob. The pounded sand rustles down the insect's

sides. The legs play but a secondary part. Stretched behind,

motionless, when the piston stroke is delivered, they furnish a

support. As the sand descends, they pile it and nimbly push it

back, after which they drag along lifelessly until the next

avalanche. The head advances each time by a length equal to that

of the sand displaced. Each stroke of the frontal swelling means a

step forward. In a dry, loose soil, things go pretty fast. A

column six inches high is traversed in less than a quarter of an

hour.



As soon as it reaches the surface, the insect, covered with dust,

proceeds to make its toilet. It thrusts out the blister of its

forehead for the last time and brushes it carefully with its front

tarsi. It is important that the little pounding engine should be

carefully dusted before it is taken inside to form a forehead that

will open no more: this lest any grit should lodge in the head.

The wings are carefully brushed and polished; they lose their

curved notches; they lengthen and spread. Then, motionless on the

surface of the sand, the fly matures fully. Let us set her at

liberty. She will go and join the others on the Snakes in my pans.