THE BLUEBOTTLE: THE GRUB

The larvae of the bluebottle hatch within two days in the warm

weather. Whether inside my apparatus, in direct contact with the

piece of meat, or outside, on the edge of a slit that enables them

to enter, they set to work at once. They do not eat, in the strict

sense of the word, that is to say, they do not tear their food, do

not chew it by means of implements of mastication. Their mouth

parts do not lend themselve to this sort of work. These mouth

parts are two horny spikes, sliding one upon the other, with curved

ends that do not face, thus excluding the possibility of any

function such as seizing and grinding.



The two guttural grapnels serve for walking much rather than for

feeding. The worm plants them alternately in the road traversed

and, by contracting its crupper, advances just that distance. It

carries in its tubular throat the equivalent of our iron tipped

sticks which give support and assist progress.



Thanks to this machinery of the mouth, the maggot not only moves

over the surface, but also easily penetrates the meat: I see it

disappear as though it were dipping into butter. It cuts its way,

levying, as it goes, a preliminary toll, but only of liquid

mouthfuls. Not the smallest solid particle is detached and

swallowed. That is not the maggot's diet. It wants a broth, a

soup, a sort of fluid extract of beef which it prepares itself. As

digestion, after all, merely means liquefaction, we may say,

without being guilty of paradox, that the grub of the bluebottle

digests its food before swallowing it.



With the object of relieving gastric troubles, our manufacturing

chemists scrape the stomachs of the pig and sheep and thus obtain

pepsin, a digestive agent which possesses the property of

liquefying albuminous matters and lean meat in particular. Why

cannot they rasp the stomach of the maggot! They would obtain a

product of the highest quality, for the carnivorous worm also owns

its pepsin, pepsin of a singularly active kind, as the following

experiments will show us.



I divide the white of a hard-boiled egg into tiny cubes and place

them in a little test-tube. On the top of the contents, I sprinkle

the eggs of the bluebottle, eggs free from the least stain, taken

from those laid on the outside of tins baited with meat and not

absolutely shut. A similar test-tube is filled with white of egg,

but receives no germs. Both are closed with a plug of cotton-wool

and left in a dark corner.



In a few days, the tube swarming with newborn vermin contains a

liquid as fluid and transparent as water. Not a drop would remain

in the tube if I turned it upside down. All the white of egg has

disappeared, liquefied. As for the worms, which are already a fair

size, they seem very ill at ease. Deprived of a support whence to

attain the outer air, most of them dive into the broth of their own

making, where they perish by drowning. Others, endowed with

greater vigor, crawl up the glass to the plug and manage to make

their way through the wadding. Their pointed front, armed with

grappling irons, is the nail that penetrates the fibrous mass.



In the other test-tube, standing beside the first and subjected to

the same atmospheric influences, nothing striking has occurred.

The hard-boiled white of egg has retained its dead white color and

its firmness. I find it as I left it. The utmost that I observe

is a few traces of must. The result of this first experiment is

patent: the Bluebottle's grub is the medium that converts

coagulated albumen into a liquid.



The value of chemist's pepsin is estimated by the quantity of hard-

boiled white of egg which a gram of that agent can liquefy. The

mixture has to be exposed in an oven to a temperature of 1400 F.

and also to be frequently shaken. My preparation, in which the

bluebottle's eggs are hatched, is neither shaken nor subjected to

the heat of an oven; everything happens in quietness and under the

thermometric conditions of the surrounding air; nevertheless, in a

few days, the coagulated albumen, treated by the vermin, runs like

water.



The reagent that causes this liquefaction escapes my endeavors to

detect it. The worms must disgorge it in infinitesimal doses,

while the spikes in their throats, which are in continual movement,

emerge a little way from the mouth, reenter and reappear. Those

piston thrusts, those quasi-kisses, are accompanied by the emission

of the solvent: at least, that is how I picture it. The maggot

spits on its food, places on it the wherewithal to make it into

broth. To appraise the quantity of the matter expectorated is

beyond my powers: I observe the result, but do not perceive the

leavening agent.



Well, this result is really astounding, when we consider the

scantiness of the means. No pig's or sheep's pepsin can rival that

of the worm. I have a bottle of pepsin that comes from the School

of Chemistry at Montpellier. I lavishly powder some pieces of

hard-boiled white of egg with the potent drug, just as I did with

the eggs of the Bluebottle. The oven is not brought into play,

neither is distilled water added, nor hydrochloric acid: two

auxiliaries which are recommended. The experiment is conducted in

exactly the same way as that of the tubes with the vermin. The

result is entirely different from what I expected. The white of

egg does not liquefy. It simply becomes moist on the surface; and

even this moisture may come from the pepsin, which is highly

absorbent. Yes, I was right: if the thing were feasible, it would

be an advantage for the chemists to collect their digestive drug

from the stomach of the maggot. The worm, in this case, beats the

pig and the sheep.



The same method is followed for the remaining experiments. I put

the bluebottle's eggs to hatch on a piece of meat and leave the

worms to do their work as they please. The lean tissues, whether

of mutton, beef or pork, no matter which, are not turned into

liquid; they become a pea soup of a clarety brown. The liver, the

lung, the spleen are attacked to better purpose, without, however,

getting beyond the state of a semi-fluid jam, which easily mixes

with water and even appears to dissolve in it. The brains do not

liquefy either: they simply melt into a thin gruel.



On the other hand, fatty substances, such as beef suet, lard and

butter, do not undergo any appreciable change. Moreover, the worms

soon dwindle away, incapable of growing. This sort of food does

not suit them. Why? Apparently because it cannot be liquefied by

the reagent disgorged by the worms. In the same way, ordinary

pepsin does not attack fatty substances; it takes pancreatin to

reduce them to an emulsion. This curious analogy of properties,

positive for albuminous, negative for fatty matter, proclaims the

similarity and perhaps the identity of the dissolvent discharged by

the grubs and the pepsin of the higher animals.



Here is another proof: the usual pepsin does not dissolve the

epidermis, which is a material of a horny nature. That of the

maggots does not dissolve it either. I can easily rear bluebottle

grubs on dead crickets whose bellies I have first opened; but I do

not succeed if the morsel be left intact: the worms are unable to

perforate the succulent paunch; they are stopped by the cuticle, on

which their reagent refuses to act. Or else I give them frogs'

hind legs, stripped of their skin. The flesh turns to broth and

disappears to the bone. If I do not peel the legs, they remain

intact in the midst of the vermin. Their thin skin is sufficient

to protect them.



This failure to act upon the epidermis explains why the bluebottle

at work on the animal declines to lay her eggs on the first part

that comes handy. She needs the delicate membrane of the nostrils,

eyes or throat, or else some wound in which the flesh is laid bare.

No other place suits her, however excellent for flavor and

darkness. At most, finding nothing better when my stratagems

interfere, she persuades herself to dab a few eggs under the axilla

of a plucked bird or in the groin, two points at which the skin is

thinner than elsewhere.



With her maternal foresight, the bluebottle knows to perfection the

choice surfaces, the only ones liable to soften and run under the

influence of the reagent dribbled by the newborn grubs. The

chemistry of the future is familiar to her, though she does not use

it for her own feeding; motherhood, that great inspirer of

instinct, teaches her all about it.



Scrupulous though she be in choosing exactly where to lay her eggs,

the bluebottle does not trouble about the quality of the provisions

intended for her family's consumption. Any dead body suits her

purpose. Redi, the Italian scientist who first exploded the old,

foolish notion of worms begotten of corruption, fed the vermin in

his laboratory with meat of very different kinds. In order to make

his tests the more conclusive, he exaggerated the largess of the

dining hall. The diet was varied with tiger and lion flesh, bear

and leopard, fox and wolf, mutton and beef, horseflesh, donkey

flesh and many others, supplied by the rich menagerie of Florence.

This wastefulness was unnecessary: wolf and mutton are all the same

to an unprejudiced stomach.



A distant disciple of the maggot's biographer, I look at the

problem in a light which Redi never dreamt of. Any flesh of one of

the higher animals suits the fly's family. Will it be the same if

the food supplied be of a lower organism and consist of fish, for

instance, of frog, mollusk, insect, centipede? Will the worms

accept these viands and, above all, can they manage to liquefy

them, which is the first and foremost condition?



I serve a piece of raw whiting. The flesh is white, delicate,

partly translucent, easy for our stomachs to digest and no less

suited to the grub's dissolvent. It turns into an opalescent

fluid, which runs like water. In fact, it liquefies in much the

same way as hard-boiled white of egg. The worms at first wax fat,

as long as the conditions allow of some solid eyots remaining;

then, when foothold fails, threatened with drowning in the too

fluid broth, they creep up the side of the glass, anxious and

restless to be off. They climb to the cotton-wool stopper of the

test-tube and try to bolt through the wadding. Endowed with

stubborn perseverance, nearly all of them decamp in spite of the

obstacle. The test-tube with the white of egg showed me a similar

exodus. Although the fare suits them, as their growth witnesses,

the worms cease feeding and make a point of escaping when death by

drowning is imminent.



With other fish, such as skate and sardines, with the flesh of

frogs and tree frogs, the meat simply dissolves into a porridge.

Hashes of slug, Scolopendra or praying mantis furnish the same

result.



In all these preparations, the dissolving agent of the worms is as

much in evidence as when butcher's meat is employed. Moreover, the

grubs seem satisfied with the queer dish which my curiosity

prescribes for them; they thrive amidst the victuals and undergo

their transformation into pupae.



The conclusion, therefore, is much more general than Redi imagined.

Any meat, no matter whether of a higher or lower order, suits the

bluebottle for the settlement of her family. The carcasses of

furred and feathered animals are the favorite victuals, probably

because of their richness, which allows of plentiful layings; but,

should the occasion demand it, the others are also accepted,

without inconvenience. Any carrion that has lived the life of an

animal comes within the domain of these scavengers.



What is their number to one mother? I have already spoken of a

deposit of three hundred, counted egg by egg. A quite fortuitous

circumstance enabled me to go much farther. In the first week of

January 1905, we experienced a sudden short cold snap of a severity

very exceptional in my part of the country. The thermometer fell

to twelve degrees below zero. While a fierce north wind was raging

and beginning to redden the leaves of the olive trees, came one and

brought me a barn or screech owl, which he had found on the ground,

exposed to the air, not far from my house. My reputation as a

lover of animals made the donor believe that I should be pleased

with his gift.



I was, as a matter of fact, but for reasons whereof the finder

certainly never dreamt. The owl was untouched, with trim feathers

and not the least wound that showed. Perhaps he had died of cold.

What made me gratefully accept the present was exactly that which

would have inclined anyone but myself to refuse it. The owl's

eyes, glazed in death, were hidden under a thick mass of eggs,

which I recognized as a bluebottle's. Similar masses occupied the

vicinity of the nostrils. If I wanted maggots, here, of a

certainty, was a richer crop than I had ever beheld.



I place the corpse on the sand of a pan, with a wire gauze cover,

and leave events to take their course. The laboratory in which I

install my bird is none other than my study. It is as cold in

there, or nearly, as outside, so much so that the water in the

aquarium in which I used to rear caddis worms has frozen into a

solid block of ice. Under these conditions of temperature, the

owl's eyes keep their white veil of germs unchanged. Nothing

stirs, nothing swarms. Weary of waiting, I pay no more attention

to the carcass; I leave the future to decide whether the cold has

exterminated the fly's family or not.



Before the end of March, the packets of eggs have disappeared, I

know not how long. The bird, for that matter, seems to be intact.

On the ventral surface, which is turned to the air, the feathers

keep their smooth arrangement and their fresh coloring. I lift the

thing. It is light, very dry and gives a hard sound, like an old

shoe tanned by the summer sun in the fields. There is no smell.

The dryness has vanquished the stench, which, in any case, was

never offensive during that time of frost. On the other hand, the

back, which touched the sand, is a loathsome wreck, partly deprived

of its feathers. The quills of the tail are bare barreled; a few

whitened bones show, deprived of their muscles. The skin has

turned into a dark leather, pierced with round holes like those of

a sieve. It is all hideously ugly, but most instructive.



The wretched owl, with his shattered backbone, teaches us, first of

all, that a temperature twelve degrees of frost does not endanger

the existence of the bluebottle's germs. The worms were born

without accident, despite the rude blast; they feasted copiously on

extract of meat; then, growing big and fat, they descended into the

earth by piercing round holes in the bird's skin. Their pupae must

now be in the sand of the pan.



They are, in point of fact, and in such numbers that I have to

resort to sifting in order to collect them. If I used the forceps,

I should never have done sorting so great a quantity. The sand

passes through the meshes of the sieve, the pupae remain above. To

count them would wear out my patience. I measure them by the

bushel, that is to say, with a thimble of which I know the holding

capacity in pupae. The result of my calculation is not far short

of nine hundred.



Does this family proceed from one mother? I am quite ready to

admit it, so unlikely is it that the bluebottle, who is so rare

inside our houses during the severe cold of winter, should be

frequent enough outside to form into groups and to do business in

common while an icy blast is raging. A belated specimen, the

plaything of the north wind, and one alone must have deposited the

burden of her ovaries on the owl's eyes. This laying of nine

hundred eggs, an incomplete laying perhaps, bears witness to the

mighty part played by the fly as a liquidator of corpses.



Before throwing away the screech owl treated by the worms, let us

overcome our repugnance and give a glance inside the bird. We see

a tortuous cavity, fenced in by nameless ruins. Muscles and bowels

have disappeared, converted into broth and gradually consumed by

the teeming throng. In every part, what was wet has become dry,

what was solid muddy. In vain my forceps ransacks every nook and

corner: it does not hit upon a single pupa. All the worms have

emigrated, all, without exception. From first to last, they have

forsaken the refuge of the corpse, so soft to their delicate skins;

they have left the velvet for the hard ground. Is dryness

necessary to them at this stage? They had it in the carcass, which

was thoroughly drained. Would they protect themselves against the

cold and rain? No shelter could suit them better than the thick

quilt of the feathers, which has remained wholly undamaged on the

belly, the breast and every part that was not in touch with the

ground. It looks as though they had fled from comfort to seek a

less kindly dwelling place. When the hour of transformation came,

all left the owl, that most excellent lodging; all dived into the

sand.



The exodus from the mortuary tabernacle was made through the round

holes wherewith the skin is pierced. Those holes are the worms'

work: of that there is no doubt; and yet we have lately seen the

mothers refuse as a bed for their eggs any part whereat the flesh

is protected by a skin of some thickness. The reason is the

failure of the pepsin to act on epidermic substances. In the

absence of liquefaction at such points, the nourishing gruel is

unprocurable. On the other hand, the tiny worms are not able--or

at least do not know how--to dig through the integument with their

pair of guttural harpoons, to rend it and reach the liquefiable

flesh. The newborn lack strength and, above all, purpose. But, as

the time comes for descending into the earth, the worms, now

powerful and suddenly versed in the necessary art, well know how to

eat away patiently and clear themselves a passage. With the hooks

of their spikes they dig, scratch and tear. Instinct has flashes

of inspiration. What the animal did not know how to do at the

start it learns without apprenticeship when the time comes to

practice this or that industry. The maggot ripe for burial

perforates a membranous obstacle which the grub intent upon its

broth would not even have attempted to attack with either its

pepsin or its grapnels.



Why does the worm quit the carcass, that capital shelter? Why does

it go and take up its abode in the ground? As the leading

disinfector of dead things, it works at the most important matter,

the suppression of the infection; but it leaves a plentiful

residuum, which does not yield to the reagents of its analytical

chemistry. These remains have to disappear in their turn. After

the fly, anatomists come hastening, who take up the dry relic,

nibble skin, tendons and ligaments and scrape the bones clean.



The greatest expert in this work is the Dermestes beetle, an

enthusiastic gnawer of animal remains. Sooner or later, he will

come to the joint already exploited by the fly. Now what would

happen if the pupae were there? The answer is obvious. The

Dermestes, who loves hard food, would dig his teeth into the horny

little kegs and demolish them at a bite. Even though he did not

touch the contents, a live thing which he probably dislikes, he

would at least test the flavor of that lifeless substance, the

container. The future Fly would be lost, because her casing would

be pierced. Even so, in the storerooms of our silk mills, a

certain Dermestes (Dermestes vulpinus, FABR.) digs into the cocoons

to attack the horny covering of the chrysalis.



The maggot foresees the danger and makes itself scarce before the

other arrives. In what sort of memory does it house so much

wisdom, indigent, headless creature that it is, for it is only by

extension that we can give the name of head to the animal's pointed

fore part? How did it learn that, to safeguard the pupa, it must

desert the carcass and that, to safeguard the fly, it must not bury

itself too far down?



To emerge from underground after the perfect insect is hatched, the

bluebottle's device consists in disjointing her head into two

movable halves, which, each distended with its great red eye, by

turns separate and reunite. In the intervening space, a large,

glassy hernia rises and disappears, disappears and rises. When the

two move asunder, with one eye forced back to the right, the other

to the left, it is as though the insect were splitting its brain

pan in order to expel the contents. Then the hernia rises, blunt

at the end and swollen into a great knob. Next, the forehead

closes and the hernia retreats, leaving visible only a kind of

shapeless muzzle. In short, a frontal pouch, with deep pulsations

momentarily renewed, becomes the instrument of deliverance, the

pestle wherewith the newly hatched bluebottle bruises the sand and

causes it to crumble. Gradually the legs push the rubbish back and

the insect advances so much toward the surface.



A hard task, this exhumation by dint of the blows of a cleft and

palpitating head. Moreover, the exhausting effort has to be made

at the moment of greatest weakness, when the insect leaves that

protecting casket, its pupa. It emerges from it pale, flabby and

unsightly, sorrily clad in the wings which, folded lengthwise and

made shorter by their scalloped edge, only just cover the top of

the back. Wildly bristling with hairs and colored ashen-gray, it

is a piteous sight. The large set of wings, suitable for flight,

will spread later. For the moment, it would only be in the way

amid the obstacles to be passed through. Later also will come the

faultless dress wherein the iridescent indigo-blue stands out

against the severity of the black.



The frontal hernia that crumbles the sand with its impact has a

tendency to make play for some time after the emergence from the

ground. Take hold with the forceps of one of the hind legs of a

newly released fly. Forthwith, the implement of the head begins to

work, swelling and subsiding as energetically as a moment ago, when

it had to make a hole in the sand. The insect, hampered in its

movements as when it was underground, struggles as best it can

against the only obstacle that it knows. With its heaving knob, it

pounds the air even as but now it pounded the earthy barrier. In

all unpleasant circumstances, its one resource is to cleave its

head and produce its cranial hernia, which moves out and in, in and

out. For nearly two hours, interspersed with halts due to fatigue,

the little machine keeps throbbing in my forceps.



In the meantime, however, the desperate one is hardening her skin;

she spreads wide the sail of her wings and dons her deep mourning

of black and darkest blue. Then her eyes, warped sideways, come

together and resume their normal position. The cleft forehead

closes; the delivering blister goes in, never to show itself again.

But there is one precaution to be taken first. With its front

tarsi, the insect carefully brushes the bump about to disappear

from view, lest grit should lodge in the cranium when the two

halves of the head are joined for good.



The maggot is aware of the trials that await it when, as a fly, it

will have to come up from under ground; it knows beforehand how

difficult the ascent will be with the feeble instrument at its

disposal, so difficult, in fact, as to become fatal should the

journey be at all prolonged. It foresees the dangers ahead of it

and averts them as well as it can. Gifted with two iron shod

sticks in its throat, it can easily descend to such depths as it

pleases. The need for greater quiet and a less trying temperature

calls for the deepest possible home: the lower down it is, the

better for the welfare of the worm and the pupa, on condition that

descent be practicable. It is, perfectly; and yet, though free to

obey its inspiration, the grub refrains. I rear it in a deep pan,

full of fine, dry sand, easy to excavate. The interment never goes

very far. About a hand's breadth is all that the most progressive

digger ventures upon. Most of the interred remain nearer still to

the surface. Here, under a thin layer of sand, the grub's skin

hardens and becomes a coffin, a casket, wherein the transformation

sleep is slept. A few weeks later, the buried one awakes,

transfigured but weak, having naught wherewith to unearth herself

but the throbbing hernia of her open forehead.



What the maggot denies itself it is open to me to realize, should I

care to know the depth whence the fly is able to mount. I place

fifteen bluebottle pupae, obtained in winter, at the bottom of a

wide tube closed at one end. Above the pupae is a perpendicular

column of fine, dry sand, the height of which varies in different

tubes. April comes and the hatching begins.



A tube with six centimeters of sand, the shallowest of the columns

under experiment, yields the best result. Of the fifteen subjects

interred in the pupa stage, fourteen easily reach the surface when

they become flies. Only one of them perishes, one who has not even

attempted the ascent. With twelve centimeters of sand, four

emerge. With twenty centimeters, two, no more. The other flies,

jaded with their exertions, have died at a higher or lower stage of

the road. Lastly, with yet another tube wherein the column of sand

measured sixty centimeters, I obtained the liberation of only a

single fly. The plucky creature must have had a hard struggle to

mount from so great a depth, for the other fourteen did not even

manage to burst the lid of their caskets.



I presume that the looseness of the sand and the consequent

pressure in every direction, similar to that exercised by fluids,

have a certain bearing on the difficulties of the exhumation. Two

more tubes are prepared, but this time supplied with fresh mould,

lightly heaped up, which has not the incoherence of sand, with the

attendant drawback of pressure. Six centimeters of mould give me

eight flies for fifteen pupae buried; twenty centimeters give me

only one. There is less success than with the sandy column. My

device has diminished the pressure, but, at the same time,

increased the passive resistance. The sand falls of itself under

the impact of the frontal rammer; the unyielding mould demands the

cutting of a gallery. In fact, I perceive, on the road followed, a

shaft which continues indefinitely such as it is. The fly has

bored it with the temporary blister that throbs between her eyes.



In every medium, therefore, whether sand, mould or any earthy

combination, great are the sufferings that attend the exhumation of

the fly. And so the maggot shuns the depths which a desire for

additional security might seem to recommend. The worm has its own

prudence: foreseeing the dangers ahead, it refrains from making

great descents that might promote the welfare of the moment. It

neglects the present for the sake of the future.