THE BLUEBOTTLE: THE LAYING





To purge the earth of death's impurities and cause deceased animal

matter to be once more numbered among the treasures of life there

are hosts of sausage queens, including, in our part of the world,

the bluebottle (Calliphora vomitaria, LIN.) and the checkered flesh

fly (Sarcophaga carnaria, LIN.). Every one knows the first, the

big, dark-blue fly who, after effecting her designs in the ill-

watched meat safe, settles on our window panes and keeps up a

solemn buzzing, anxious to be off in the sun and ripen a fresh

emission of germs. How does she lay her eggs, the origin of the

loathsome maggot that battens poisonously on our provisions,

whether of game or butcher's meat? What are her stratagems and how

can we foil them? This is what I propose to investigate.



The bluebottle frequents our homes during autumn and a part of

winter, until the cold becomes severe; but her appearance in the

fields dates back much earlier. On the first fine day in February,

we shall see her warming herself, chillily, against the sunny

walls. In April, I notice her in considerable numbers on the

laurestinus. It is here that she seems to pair, while sipping the

sugary exudations of the small white flowers. The whole of the

summer season is spent out of doors, in brief flights from one

refreshment bar to the next. When autumn comes, with its game, she

makes her way into our houses and remains until the hard frosts.



This suits my stay-at-home habits and especially my legs, which are

bending under the weight of years. I need not run after the

subjects of my present study; they call on me. Besides, I have

vigilant assistants. The household knows of my plans. Every one

brings me, in a little screw of paper, the noisy visitor just

captured against the panes.



Thus do I fill my vivarium, which consists of a large, bell-shaped

cage of wire gauze, standing in an earthenware pan full of sand. A

mug containing honey is the dining room of the establishment. Here

the captives come to recruit themselves in their hours of leisure.

To occupy their maternal cares, I employ small birds--chaffinches,

linnets, sparrows--brought down, in the enclosure, by my son's gun.



I have just served up a Linnet shot two days ago. I next place in

the cage a bluebottle, one only, to avoid confusion. Her fat belly

proclaims the advent of a laying time. An hour later, when the

excitement of being put in prison is allayed, my captive is in

labor. With eager, jerky steps, she explores the morsel of game,

goes from the head to the tail, returns from the tail to the head,

repeats the action several times and at last settles near an eye, a

dimmed eye sunk into its socket.



The ovipositor bends at a right angle and dives into the junction

of the beak, straight down to the root. Then the eggs are emitted

for nearly half an hour. The layer, utterly absorbed in her

serious business, remains stationary and impassive and is easily

observed through my lens. A movement on my part would doubtless

scare her; but my restful presence gives her no anxiety. I am

nothing to her.



The discharge does not go on continuously until the ovaries are

exhausted; it is intermittent and performed in so many packets.

Several times over, the fly leaves the bird's beak and comes to

take a rest upon the wire gauze, where she brushes her hind legs

one against the other. In particular, before using it again, she

cleans, smoothes and polishes her laying tool, the probe that

places the eggs. Then, feeling her womb still teeming, she returns

to the same spot at the joint of the beak. The delivery is

resumed, to cease presently and then begin anew. A couple of hours

are thus spent in alternate standing near the eye and resting on

the wire gauze.



At last, it is over. The fly does not go back to the bird, a proof

that her ovaries are exhausted. The next day, she is dead. The

eggs are dabbed in a continuous layer, at the entrance to the

throat, at the root of the tongue, on the membrane of the palate.

Their number appears considerable; the whole inside of the gullet

is white with them. I fix a little wooden prop between the two

mandibles of the beak, to keep them open and enable me to see what

happens.



I learn in this way that the hatching takes place in a couple of

days. As soon as they are born, the young vermin, a swarming mass,

leave the place where they are and disappear down the throat. To

inquire further into the work is useless for the moment. We shall

learn more about it later, under conditions that make examination

easier.



The beak of the bird invaded was closed at the start, as far as the

natural contact of the mandibles allowed. There remained a narrow

slit at the base, sufficient at most to admit the passage of a

horsehair. It was through this that the laying was performed.

Lengthening her ovipositor like a telescope, the mother inserted

the point of her implement, a point slightly hardened with a horny

armor. The fineness of the probe equals the fineness of the

aperture. But, if the beak were entirely closed, where would the

eggs be laid then?



With a tied thread, I keep the two mandibles in absolute contact;

and I place a second bluebottle in the presence of the linnet,

which the colonists have already entered by the beak. This time,

the laying takes place on one of the eyes, between the lid and the

eyeball. At the hatching, which again occurs a couple of days

later, the grubs make their way into the fleshy depths of the

socket. The eyes and the beak, therefore, form the two chief

entrances into feathered game.



There are others; and these are the wounds. I cover the linnet's

head with a paper hood which will prevent invasion through the beak

and eyes. I serve it, under the wire gauze bell, to a third egg

layer. The bird has been struck by a shot in the breast, but the

sore is not bleeding: no outer stain marks the injured spot.

Moreover, I am careful to arrange the feathers, to smooth them with

a hair pencil, so that the bird looks quite smart and has every

appearance of being untouched.



The fly is soon there. She inspects the linnet from end to end;

with her front tarsi she fumbles at the breast and belly. It is a

sort of auscultation by sense of touch. The insect becomes aware

of what is under the feathers by the manner in which these react.

If scent comes to her assistance, it can only be very slightly, for

the game is not yet high. The wound is soon found. No drop of

blood is near it, for it is closed by a plug of down rammed into it

by the shot. The fly takes up her position without separating the

feathers or uncovering the wound. She remains here for two hours

without stirring, motionless, with her abdomen concealed beneath

the plumage. My eager curiosity does not distract her from her

business for a moment.



When she has finished, I take her place. There is nothing either

on the skin or at the mouth of the wound. I have to withdraw the

downy plug and dig to some depth before discovering the eggs. The

ovipositor has therefore lengthened its extensible tube and pushed

beyond the feather stopper driven in by the lead. The eggs are in

one packet; they number about three hundred.



When the beak and eyes are rendered inaccessible, when the body,

moreover, has no wounds, the laying still takes place, but, this

time, in a hesitating and niggardly fashion. I pluck the bird

completely, the better to watch what happens; also, I cover the

head with a paper hood to close the usual means of access. For a

long time, with jerky steps, the mother explores the body in every

direction; she takes her stand by preference on the head, which she

sounds by tapping on it with her front tarsi. She knows that the

openings which she needs are there, under the paper; but she also

knows how frail are her grubs, how powerless to pierce their way

through the strange obstacle which stops her as well and interferes

with the work of her ovipositor. The cowl inspires her with

profound distrust. Despite the tempting bait of the veiled head,

not an egg is laid on the wrapper, slight though it may be.



Weary of vain attempts to compass this obstacle, the Fly at last

decides in favor of other points, but not on the breast, belly or

back, where the hide would seem too tough and the light too

intrusive. She needs dark hiding places, corners where the skin is

very delicate. The spots chosen are the cavity of the axilla,

corresponding with our armpit, and the crease where the thigh joins

the belly. Eggs are laid in both places, but not many, showing

that the groin and the axilla are adopted only reluctantly and for

lack of a better spot.



With an unplucked bird, also hooded, the same experiment failed:

the feathers prevent the fly from slipping into those deep places.

Let us add, in conclusion, that, on a skinned bird, or simply on a

piece of butcher's meat, the laying is effected on any part

whatever, provided that it be dark. The gloomiest corners are the

favorite ones.



It follows from all this that, to lay the eggs, the Bluebottle

picks out either naked wounds or else the mucous membranes of the

mouth or eyes, which are not protected by a skin of any thickness.

She also needs darkness. We shall see the reasons for her

preference later on.



The perfect efficiency of the paper bag, which prevents the inroads

of the worms through the eye sockets or the beak, suggests a

similar experiment with the whole bird. It is a matter of wrapping

the body in a sort of artificial skin which will be as discouraging

to the fly as the natural skin. Linnets, some with deep wounds,

others almost intact, are placed one by one in paper envelopes

similar to those in which the nursery gardener keeps his seeds,

envelopes just folded, without being stuck. The paper is quite

ordinary and of average thickness. Torn pieces of newspaper serve

the purpose.



These sheaths with the corpses inside them are freely exposed to

the air, on the table in my study, where they are visited,

according to the time of day, in dense shade and in bright

sunlight. Attracted by the effluvia from the dead meat, the

bluebottles haunt my laboratory, the windows of which are always

open. I see them daily alighting on the envelopes and very busily

exploring them, apprised of the contents by the gamy smell. Their

incessant coming and going is a sign of intense cupidity; and yet

none of them decides to lay on the bags. They do not even attempt

to slide their ovipositor through the slits of the folds. The

favorable season passes and not an egg is laid on the tempting

wrappers. All the mothers abstain, judging the slender obstacle of

the paper to be more than the vermin will be able to overcome.



This caution on the fly's part does not at all surprise me:

motherhood everywhere has gleams of great perspicacity. What does

astonish me is the following result. The parcels containing the

linnets are left for a whole year uncovered on the table; they

remain there for a second year and a third. I inspect the contents

from time to time. The little birds are intact, with unrumpled

feathers, free from smell, dry and light, like mummies. They have

become not decomposed, but mummified.



I expected to see them putrefying, running into sanies, like

corpses left to rot in the open air. On the contrary, the birds

have dried and hardened, without undergoing any change. What did

they want for their putrefaction? Simply the intervention of the

fly. The maggot, therefore, is the primary cause of dissolution

after death; it is, above all, the putrefactive chemist.



A conclusion not devoid of value may be drawn from my paper game

bags. In our markets, especially in those of the South, the game

is hung unprotected from the hooks on the stalls. Larks strung up

by the dozen with a wire through their nostrils, thrushes, plovers,

teal, partridges, snipe, in short, all the glories of the spit

which the autumn migration brings us, remain for days and weeks at

the mercy of the flies. The buyer allows himself to be tempted by

a goodly exterior; he makes his purchase and, back at home, just

when the bird is being prepared for roasting, he discovers that the

promised dainty is alive with worms. O horror! There is nothing

for it but to throw the loathsome, verminous thing away.



The bluebottle is the culprit here. Everybody knows it; and nobody

thinks of seriously shaking off her tyranny: not the retailer, nor

the wholesale dealer, nor the killer of the game. What is wanted

to keep the maggots out? Hardly anything: to slip each bird into a

paper sheath. If this precaution were taken at the start, before

the flies arrive, any game would be safe and could be left

indefinitely to attain the degree of ripeness required by the

epicure's palate.



Stuffed with olives and myrtle berries, the Corsican blackbirds are

exquisite eating. We sometimes receive them at Orange, layers of

them, packed in baskets through which the air circulates freely and

each contained in a paper wrapper. They are in a state of perfect

preservation, complying with the most exacting demands of the

kitchen. I congratulate the nameless shipper who conceived the

bright idea of clothing his blackbirds in paper. Will his example

find imitators? I doubt it.



There is, of course, a serious objection to this method of

preservation. In its paper shroud, the article is invisible; it is

not enticing; it does not inform the passer by of its nature and

qualities. There is one resource left which would leave the bird

uncovered: simply to case the head in a paper cap. The head being

the part most threatened, because of the mucus membrane of the

throat and eyes, it would be sufficient, as a rule, to protect the

head, in order to keep off the Flies and to thwart their attempts.



Let us continue to study the bluebottle, while varying our means of

information. A tin, about four inches deep, contains a piece of

butcher's meat. The lid is not put in quite straight and leaves a

narrow slit at one point of its circumference, allowing, at most,

of the passage of a fine needle. When the bait begins to give off

a gamy scent, the mothers come. Singly or in numbers. They are

attracted by the odor which, transmitted through a thin crevice,

hardly reaches my nostrils.



They explore the metal receptacle for some time, seeking an

entrance. Finding naught that enables them to reach the coveted

morsel, they decide to lay their eggs on the tin, just beside the

aperture. Sometimes, when the width of the passage allows of it,

they insert the ovipositor into the tin and lay the eggs inside, on

the very edges of the slit. Whether outside or in, the eggs are

dabbed down in a fairly regular and absolutely white layer. I as

it were shovel them up with a little paper scoop. I thus obtain

all the germs that I require for my experiments, eggs bearing no

trace of the stains which would be inevitable if I had to collect

them on tainted meat.



We have seen the bluebottle refusing to lay her eggs on the paper

bag, notwithstanding the carrion fumes of the Linnet enclosed; yet

now, without hesitation, she lays them on a sheet of metal. Can

the nature of the floor make any difference to her? I replace the

tin lid by a paper cover stretched and pasted over the orifice.

With the point of my knife, I make a narrow slit in this new lid.

That is quite enough: the parent accepts the paper.



What determined her, therefore, is not simply the smell, which can

easily be perceived even through the uncut paper, but, above all,

the crevice, which will provide an entrance for the vermin, hatched

outside, near the narrow passage. The maggots' mother has her own

logic, her prudent foresight. She knows how feeble her wee grubs

will be, how powerless to cut their way through an obstacle of any

resistance; and so, despite the temptation of the smell, she

refrains from laying so long as she finds no entrance through which

the newborn worms can slip unaided.



I wanted to know whether the color, the shininess, the degree of

hardness and other qualities of the obstacle would influence the

decision of a mother obliged to lay her eggs under exceptional

conditions. With this object in view, I employed small jars, each

baited with a bit of butcher's meat. The respective lids were made

of different colored paper, of oilskin, or of some of that tinfoil,

with its gold or coppery sheen, which is used for sealing liqueur

bottles. On not one of these covers did the mothers stop, with any

desire to deposit their eggs; but, from the moment that the knife

had made the narrow slit, all the lids were, sooner or later,

visited and all of them, sooner or later, received the white shower

somewhere near the gash. The look of the obstacle, therefore, does

not count; dull or brilliant, drab or colored: these are details of

no importance; the thing that matters is that there should be a

passage to allow the grubs to enter.



Though hatched outside, at a distance from the coveted morsel, the

newborn worms are well able to find their refectory. As they

release themselves from the egg, without hesitation, so accurate is

their scent, they slip beneath the edge of the ill-joined lid, or

through the passage cut by the knife. Behold them entering upon

their promised land, their reeking paradise.



Eager to arrive, do they drop from the top of the wall? Not they!

Slowly creeping, they make their way down the side of the jar; they

use their fore part, ever in quest of information, as a crutch and

grapnel in one. They reach the meat and at once install themselves

upon it.



Let us continue our investigation, varying the conditions. A large

test-tube, measuring nine inches high, is baited at the bottom with

a lump of butcher's meat. It is closed with wire gauze, whose

meshes, two millimeters wide, do not permit of the fly's passage.

The bluebottle comes to my apparatus, guided by scent rather than

sight. She hastens to the test tube whose contents are veiled

under an opaque cover with the same alacrity as to the open tube.

The invisible attracts her quite as much as the visible.



She stays a while on the lattice of the mouth, inspects it

attentively; but, whether because circumstances have failed to

serve me, or because the wire network inspires her with distrust, I

never saw her dab her eggs upon it for certain. As her evidence

was doubtful, I had recourse to the flesh fly (Sarcophaga

carnaria).



This fly is less finicky in her preparations, she has more faith in

the strength of her worms, which are born ready-formed and

vigorous, and easily shows me what I wish to see. She explores the

trellis-work, chooses a mesh through which she inserts the tip of

her abdomen and, undisturbed by my presence, emits, one after the

other, a certain number of grubs, about ten or so. True, her

visits will be repeated, increasing the family at a rate of which I

am ignorant.



The newborn worms, thanks to a slight viscidity, cling for a moment

to the wire gauze; they swarm, wriggle, release themselves and leap

into the chasm. It is a nine inch drop at least. When this is

done, the mother makes off, knowing for a certainty that her

offspring will shift for themselves. If they fall on the meat,

well and good; if they fall elsewhere, they can reach the morsel by

crawling.



This confidence in the unknown factor of the precipice, with no

indication but that of smell, deserves fuller, investigation. From

what height will the flesh fly dare to let her children drop? I

top the test-tube with another tube, the width of the neck of a

claret bottle. The mouth is closed either with wire gauze, or with

a paper cover with a slight cut in it. Altogether, the apparatus

measures twenty-five inches in height. No matter: the fall is not

serious for the lithe backs of the young grubs; and, in a few days,

the test-tube is filled with larvae, in which it is easy to

recognize the flesh fly's family by the fringed coronet that opens

and shuts at the maggot's stern like the petals of a little flower.

I did not see the mother operating: I was not there at the time;

but there is no doubt possible of her coming nor of the great dive

taken by the family: the contents of the test-tube furnish me with

a duly authenticated certificate.



I admire the leap and, to obtain one better still, I replace the

tube by another, so that the apparatus now stands forty-six inches

high. The column is erected at a spot frequented by flies, in a

dim light. Its mouth, closed with a wire gauze cover, reaches the

level of various other appliances, test-tubes and jars, which are

already stocked or awaiting their colony of vermin. When the

position is well known to the flies, I remove the other tubes and

leave the column, lest the visitors should turn aside to easier

ground.



From time to time, the bluebottle and the flesh fly perch on the

trellis-work, make a short investigation and then decamp.

Throughout the summer season, for three whole months, the apparatus

remains where it is, without the least result: never a worm. What

is the reason? Does the stench of the meat not spread, coming from

that depth? Certainly it spreads: it is unmistakable to my dulled

nostrils and still more so to the nostrils of my children, whom I

call to bear witness. Then why does the flesh fly, who but now was

dropping her grubs from a goodly height, refuse to let them fall

from the top of a column twice as high? Does she fear lest her

worms should be bruised by an excessive drop? There is nothing

about her to point to anxiety aroused by the length of the shaft.

I never see her explore the tube or take its size. She stands on

the trellised orifice; and there the matter ends. Can she be

apprised of the depth of the chasm by the comparative faintness of

the offensive odors that arise from it? Can the sense of smell

measure the distance and judge whether it be acceptable or not?

Perhaps.



The fact remains that, despite the attraction of the scent, the

flesh fly does not expose her worms to disproportionate falls. Can

she know beforehand that, when the chrysalides break, her winged

family, knocking with a sudden flight against the sides of a tall

chimney, will be unable to get out? This foresight would be in

agreement with the rules which order maternal instinct according to

future needs.



But when the fall does not exceed a certain depth, the budding

worms of the flesh fly are dropped without a qualm, as all our

experiments show. This principle has a practical application which

is not without its value in matters of domestic economy. It is as

well that the wonders of entomology should sometimes give us a hint

of commonplace utility.



The usual meat safe is a sort of large cage with a top and bottom

of wood and four wire gauze sides. Hooks fixed into the top are

used whereby to hang pieces which we wish to protect from the

flies. Often, so as to employ the space to the best advantage,

these pieces are simply laid on the floor on the cage. With these

arrangements, are we sure of warding off the fly and her vermin?



Not at all. We may protect ourselves against the Bluebottle, who

is not much inclined to lay her eggs at a distance from the meat;

but there is still the flesh fly, who is more venturesome and goes

more briskly to work and who will slip the grubs through a hole in

the meshes and drop them inside the safe. Agile as they are and

well able to crawl, the worms will easily reach anything on the

floor; the only things secure from their attacks will be the pieces

hanging from the ceiling. It is not in the nature of maggots to

explore the heights, especially if this implies climbing down a

string in addition.



People also use wire gauze dish covers. The trellised dome

protects the contents even less than does the meat safe. The flesh

fly takes no heed of it. She can drop her worms through the meshes

on the covered joint.



Then what are we to do? Nothing could be simpler. We need only

wrap the birds which we wish to preserve--thrushes, partridges,

snipe and so on--in separate paper envelopes; and the same with our

beef and mutton. This defensive armor alone, while leaving ample

room for the air to circulate, makes any invasion by the worms

impossible, even without a cover or a meat safe: not that paper

possesses any special preservative virtues, but solely because it

forms an impenetrable barrier. The Bluebottle carefully refrains

from laying her eggs upon it and the flesh fly from bringing forth

her offspring, both of them knowing that their newborn young are

incapable of piercing the obstacle.



Paper is equally successful in our strife against the Moths, those

plagues of our furs and clothes. To keep away these wholesale

ravages, people generally use camphor, naphthalene, tobacco,

bunches of lavender and other strong-scented remedies. Without

wishing to malign those preservatives, we are bound to admit that

the means employed are none too effective. The smell does very

little to prevent the havoc of the moths.



I would therefore counsel our housewives, instead of all this

chemist's stuff, to use newspapers of a suitable shape and size.

Take whatever you wish to protect--your furs, your flannel or your

clothes--and pack each article carefully in a newspaper, joining

the edges with a double fold, well pinned. If this joining is

properly done, the Moth will never get inside. Since my advice has

been taken and this method employed in my household, the old damage

has never been repeated.



To return to the fly. A piece of meat is hidden in a jar under a

layer of fine, dry sand, a finger's-breadth thick. The jar has a

wide mouth and is left quite open. Let whoever come that will,

attracted by the smell. The Bluebottles are not long in inspecting

what I have prepared for them: they enter the jar, go out and come

back again, inquiring into the invisible thing revealed by its

fragrance. A diligent watch enables me to see them fussing about,

exploring the sandy expanse, tapping it with their feet, sounding

it with their proboscis. I leave the visitors undisturbed for a

fortnight or three weeks. None of them lays any eggs.



This is a repetition of what the paper bag, with its dead bird,

showed me. The flies refuse to lay on the sand, apparently for the

same reasons. The paper was considered an obstacle which the frail

vermin would not be able to overcome. With sand, the case is

worse. Its grittiness would hurt the newborn weaklings, its

dryness would absorb the moisture indispensable to their movements.

Later, when preparing for the metamorphosis, when their strength

has come to them, the grubs will dig the earth quite well and be

able to descend; but, at the start, that would be very dangerous

for them. Knowing these difficulties, the mothers, however greatly

tempted by the smell, abstain from breeding. As a matter of fact,

after long waiting, fearing lest some packets of eggs may have

escaped my attention, I inspect the contents of the jar from top to

bottom. Meat and sand contain neither larvae nor pupae: the whole

is absolutely deserted.



The layer of sand being only a finger's-breadth thick, this

experiment requires certain precautions. The meat may expand a

little, in going bad, and protrude in one or two places. However

small the fleshy eyots that show above the surface, the flies come

to them and breed. Sometimes also the juices oozing from the

putrid meat soak a small extent of the sandy floor. That is enough

for the maggot's first establishment. These causes of failure are

avoided with a layer of sand about an inch thick. Then the

bluebottle, the flesh fly and other flies whose grubs batten on

dead bodies are kept at a proper distance.



In the hope of awakening us to a proper sense of our

insignificance, pulpit orators sometimes make an unfair use of the

grave and its worms. Let us put no faith in their doleful

rhetoric. The chemistry of man's final dissolution is eloquent

enough of our emptiness: there is no need to add imaginary horrors.

The worm of the sepulchre is an invention of cantankerous minds,

incapable of seeing things as they are. Covered by but a few

inches of earth, the dead can sleep their quiet sleep: no fly will

ever come to take advantage of them.



At the surface of the soil, exposed to the air, the hideous

invasion is possible; ay, it is the invariable rule. For the

melting down and remolding of matter, man is no better, corpse for

corpse, than the lowest of the brutes. Then the fly exercises her

rights and deals with us as she does with any ordinary animal

refuse. Nature treats us with magnificent indifference in her

great regenerating factory: placed in her crucibles, animals and

men, beggars and kings are one and all alike. There you have true

equality, the only equality in this world of ours: equality in the

presence of the maggot.





THE BLUEBOTTLE: THE GRUB THE BUMBLEBEE FLY facebooktwittergoogle_plusredditpinterestlinkedinmail

Feedback