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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.





Next: THE BLUEBOTTLE: THE GRUB

Previous: MATHEMATICAL MEMORIES: MY LITTLE TABLE



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