VIEW THE MOBILE VERSION of www.bugsinsects.net Informational Site Network Informational
Privacy
   Home - Articles - Books

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 themselves 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.





Next: A PARASITE OF THE MAGGOT

Previous: THE BLUEBOTTLE: THE LAYING



Add to del.icio.us Add to Reddit Add to Digg Add to Del.icio.us Add to Google Add to Twitter Add to Stumble Upon
Add to Informational Site Network
Report
Privacy
SHAREADD TO EBOOK