I made the acquaintance of the Anthrax in 1855 at Carpentras, at the
time when the life history of the oil beetles was causing me to search
the tall slopes beloved of the Anthophora bees [mason bees]. Her curious
pupae, so powerfully equipped to force an outlet for the perfect
insect incapable of the least effort, those pupae armed with a multiple
plowshare at the fore, a trident at the rear and rows of harpoons on the
back wherewith to rip open the Osmia bee's cocoon and break through
the hard crust of the hillside, betokened a field that was worth
cultivating. The little that I said about her at the time brought me
urgent entreaties: I was asked for a circumstantial chapter on the
strange fly. The stern necessities of life postponed to an ever
retreating future my beloved investigations, so miserably stifled.
Thirty years have passed; at last, a little leisure is at hand; and
here, in the harmas of my village, with an ardor that has in no wise
grown old, I have resumed my plans of yore, still alive like the coal
smoldering under the ashes. The Anthrax has told me her secrets, which I
in my turn am going to divulge. Would that I could address all those who
cheered me on this path, including first and foremost the revered Master
of the Landes [Leon Dufour]. But the ranks have thinned, many have been
promoted to another world and their disciple lagging behind them can but
record, in memory of those who are no more, the story of the insect clad
in deepest mourning.
In the course of July, let us give a few sideward knocks to the bracing
pebbles and detach the nests of the Chalicodoma of the Walls [a mason
bee] from their supports. Loosened by the shock, the dome comes off
cleanly, all in one piece. Moreover--and this is a great advantage--the
cells come into view wide open on the base of the exposed nest, for at
this point they have no other wall than the surface of the pebble. In
this way, without any scraping, which would be wearisome work for the
operator and dangerous to the inhabitants of the dome, we have all the
cells before our eyes, together with their contents, consisting of a
silky, amber-yellow cocoon, as delicate and translucent as an onion
peeling. Let us split the dainty wrapper with the scissors, chamber by
chamber, nest by nest. If fortune be at all propitious, as it always is
to the persevering, we shall end by finding that the cocoons harbor two
larvae together, one more or less faded in appearance, the other fresh
and plump. We shall also find some, no less plentiful, in which the
withered larva is accompanied by a family of little grubs wriggling
uneasily around it.
Examination at once reveals the tragedy that is happening under the
cover of the cocoon. The flacid and faded larva is the mason bee's.
A month ago, in June, having finished its mess of honey, it wove its
silken sheath for a bedchamber wherein to take the long sleep which is
the prelude to the metamorphosis. Bulging with fat, it is a rich and
defenseless morsel for whoever is able to reach it. Then, in spite
of apparently insurmountable obstacles, the mortar wall and the tent
without an opening, the flesh-eating larvae appeared in the secret
retreat and are now glutting themselves on the sleeper. Three different
species take part in the carnage, often in the same nest, in adjoining
cells. The diversity of shapes informs us of the presence of more than
one enemy; the final stage of the creatures will tell us the names and
qualities of the three invaders.
Forestalling the secrets of the future for the sake of greater
clearness, I will anticipate the actual facts and come at once to the
results produced. When it is by itself on the body of the mason bee's
larva, the murderous grub belongs either to Anthrax trifasciata, MEIGEN,
or to Leucospis gigas, FAB. But, if numerous little worms, often a score
and more, swarm around the victim, then it is a Chalcidid's family which
we have before us. Each of these ravagers shall have its biography. Let
us begin with the Anthrax.
And first the grub, as it is after consuming its victim, when it remains
the sole occupant of the mason bee's cocoon. It is a naked worm, smooth,
legless and blind, of a creamy dead white, each segment a perfect ring,
very much curved when at rest, but with the tendency to become
almost straight when disturbed. Through the diaphanous skin, the lens
distinguishes patches of fat, which are the cause of its characteristic
coloring. When younger, as a tiny grub a few millimeters long, it is
streaked with two different kinds of stains, some white, opaque and of a
creamy tint, others translucent and of the palest amber. The former
come from adipose masses in course of formation; the second from the
nourishing fluid or from the blood which laves those masses.
Including the head, I count thirteen segments. In the middle of the body
these segments are well marked, being separated by a slight groove; but
in the forepart they are difficult to count. The head is small and is
soft, like the rest of the body, with no sign of any mouth parts even
under the close scrutiny of the lens. It is a white globule, the size
of a tiny pin's head and continued at the back by a pad a little larger,
from which it is separated by a scarcely appreciable crease. The whole
is a sort of nipple swelling slightly on the upper surface; and its
double structure is so difficult to perceive that at first we take it
for the animal's head alone, though it includes both the head and the
prothorax, or first segment of the thorax.
The mesothorax, or middle segment of the thorax, which is two or three
times larger in diameter, is flattened in front and separated from the
nipple formed by the prothorax and the head by a deep, narrow, curved
fissure. On its front surface are two pale red stigmata, or respiratory
orifices, placed pretty close together. The metathorax, or last segment
of the thorax, is a little larger still in diameter and protrudes.
These abrupt increases in circumference result in a marked hump, sloping
sharply towards the front. The nipple of which the head forms part is
set at the bottom of this hump.
After the metathorax, the shape becomes regular and cylindrical, while
decreasing slightly in girth in the last two or three segments. Close to
the line of separation of the last two rings, I am able to distinguish,
not without difficulty, two very small stigmata, just a little darker
in color. They belong to the last segment. In all, four respiratory
orifices, two in front and two behind, as is the rule among Flies. The
length of the full sized larva is 15 to 20 millimeters and its breadth 5
to 6.
Remarkable in the first place by the protuberance of its thorax and
the smallness of its head, the grub of the Anthrax acquires exceptional
interest by its manner of feeding. Let us begin by observing that,
deprived of all, even the most rudimentary walking apparatus, the animal
is absolutely incapable of shifting its position. If I disturb its rest,
it curves and straightens itself in turns by a series of contractions,
it tosses about violently where it lies, but does not manage to
progress. It fidgets and gets no farther. We shall see later the
magnificent problem raised by this inertness.
For the moment, a most unexpected fact claims all our attention. I refer
to the extreme readiness with which the Anthrax' larva quits and returns
to the Chalicodoma grub on which it is feeding. After witnessing flesh
eating larvae at hundreds and hundreds of meals, I suddenly find myself
confronted with a manner of eating that bears no relation to anything
which I have seen before. I feel myself in a world that baffles my old
experience. Let us recall the table manners of a larva living on prey,
the Ammophila's for instance, when devouring its caterpillar. A hole is
made in the victim's side; and the head and neck of the nursling dive
deep into the wound, to root luxuriously among the entrails. There is
never a withdrawal from the gnawed belly, never a recoil to interrupt
the feast and to take breath awhile. The vivacious animal always goes
forward, chewing, swallowing, digesting, until the caterpillar's skin is
emptied of its contents. Once seated at table, it does not budge as long
as the victuals last. To tease it with a straw is not always enough
to induce it to withdraw its head outside the wound; I have to use
violence. When removed by force and then left to its own devices, the
creature hesitates for a long time, stretches itself and mouths around,
without trying to open a passage through a new wound. It needs the
attacking point that has just been abandoned. If it finds the spot,
it makes its way in and resumes the work of eating; but its future is
jeopardized from this time forward, for the game, now perhaps tackled at
inopportune points, is liable to go bad.
With the Anthrax' grub, there is none of this mangling, none of this
persistent clinging to the entrance wound. I have but to tease it with
the tip of a hair pencil and forthwith it retires; and the lens reveals
no wound at the abandoned spot, no such effusion of blood as there would
be if the skin were perforated. When its sense of security is restored,
the grub once more applies its pimple head to the fostering larva,
at any point, no matter where; and, so long as my curiosity does not
prevent it, keeps itself fixed there, without the least effort, or the
least perceptible movement that could account for the adhesion. If I
repeat the touch with the pencil, I see the same sudden retreat and,
soon after, the same contact just as readily renewed.
This facility for gripping, quitting and regripping, now here, now
there and always without a wound, the part of the victim whence the
nourishment is drawn tells us of itself that the mouth of the Anthrax
is not armed with mandibular fangs capable of digging into the skin and
tearing it. If the flesh were gashed by any such pincers, one or two
attempts would be necessary before they could be released or reapplied;
besides, each point bitten would display a lesion. Well, there is
nothing of the kind: a conscientious examination through the magnifying
glass shows conclusively that the skin is intact; the grub glues
its mouth to its prey or withdraws it with an ease that can only be
explained by a process of simple contact. This being so, the Anthrax
does not chew its food as do the other carnivorous grubs; it does not
eat, it inhales.
This method of taking nourishment implies an exceptional apparatus of
the mouth, into which it behooves us to inquire before continuing. My
most powerful magnifying glass at last discovers, at the center of the
pimple head, a small spot of an amber-russet color; and that is all. For
a more exhaustive examination we will employ the microscope. I cut off
the strange pimple with the scissors, wash it in a drop of water and
place it on the object slide. The mouth now stands revealed as a round
spot which, for hue and for the smallness of its size, may be compared
with the front stigmata. It is a small conical crater, with sides of a
pale yellowish-red and with faint, more or less concentric lines. At the
bottom of this funnel is the opening of the gullet, itself tinted red in
front and promptly spreading into a cone at the back. There is not the
slightest trace of mandibular fangs, of jaws, of mouth parts for seizing
and grinding. Everything is reduced to the bowl shaped opening, with a
delicate lining of horny texture, as is shown by the amber hue and
the concentric streaks. When I look for some term to designate this
digestive entrance, of which so far I know no other example, I can find
only that of a sucker or cupping glass. Its attack is a mere kiss, but
what a perfidious kiss!
We know the machine; now let us see the working. To facilitate
observation, I shifted the newborn Anthrax grub, together with the
Chalicodoma grub, its wet nurse, from the natal cell into a glass tube.
I was thus able, by employing as many tubes as I wanted, to follow from
start to finish, in all its most intimate details, the strange repast
which I am going to describe.
The worm is fixed by its sucker to any convenient part of the nurse,
plump and fat as butter. It is ready to break off its kiss suddenly,
should anything disquiet it, and to resume it as easily when
tranquillity is restored. No Lamb enjoys greater liberty with its
mother's teat. After three or four days of this contact of the nurse and
nursling, the former, at first replete and endowed with the glossy skin
that is a sign of health, begins to assume a withered aspect. Her sides
fall in, her fresh color fades, her skin becomes covered with little
folds and gives evidence of an appreciable shrinking in this breast
which, instead of milk, yields fat and blood. A week is hardly past
before the progress of the exhaustion becomes startlingly rapid. The
nurse is flabby and wrinkled, as though borne down by her own weight,
like a very slack object. If I move her from her place, she flops and
sprawls like a half-filled water bottle over the new supporting plane.
But the Anthrax' kiss goes on emptying her: soon she is but a sort of
shriveled lard bag, decreasing from hour to hour, from which the sucker
draws a few last oily drains. At length, between the twelfth and the
fifteenth day, all that remains of the larva of the mason bee is a white
granule, hardly as large as a pin's head.
This granule is the water bottle drained to the last drop, is the
nurse's breast emptied of all its contents. I soften the meager remnant
in water; then, keeping it still immersed, I blow into it through
an extremely attenuated glass tube. The skin fills out, distends and
resumes the shape of the larva, without there being an outlet anywhere
for the compressed air. It is intact, therefore; it is free of any
perforation, which would be forthwith revealed under the water by an
escape of gas. And so, under the Anthrax' cupping glass, the oily bottle
has been drained by a simple transpiration through the membrane; the
substance of the nurse grub has been transfused into the body of the
nursling by a process akin to that known in physics as endosmosis. What
should we say to a method of being suckled by the mere application of
the mouth to a teatless breast? What we see here may be compared with
that: without any outlet, the milk of the Chalicodoma grub passes into
the stomach of the Anthrax' larva.
Is it really an instance of endosmosis? Might it not rather be
atmospheric pressure that stimulates the flow of nourishing fluids and
distils them into the Anthrax' cup-shaped mouth, working, in order to
create a vacuum, almost like the suckers of the Cuttlefish? All this
is possible, but I shall refrain from deciding, preferring to assign a
large share to the unknown in this extraordinary method of nutrition.
It ought, I think, to provide physiologists with a field of research
in which new views on the hydrodynamics of live fluids might well be
gleaned; and this field trenches upon others that would also yield
rich harvests. The brief span of my days compels me to set the problem
without seeking to solve it.
And the second problem is this: the Chalicodoma grub destined to feed
the Anthrax is without a wound of any kind. The mother of the tiny larva
is a feeble Fly deprived of whatsoever weapon capable of injuring her
offspring's prey. Moreover, she is absolutely powerless to penetrate the
mason bee's fortress, powerless as a fluff of down against a rock. On
this point there is no doubt: the future wet nurse of the Anthrax has
not been paralyzed as are the live provisions collected by the Hunting
Wasps; she has received no bite nor scratch nor contusion of any sort;
she has experienced nothing out of the common: in short, she is in her
normal state. The billeted nursling arrives, we shall presently see how;
he arrives, scarcely visible, almost defying the scrutiny of the lens;
and, having made his preparations, he installs himself, he, the atom,
upon the monstrous nurse, whom he is to drain to the very husk. And she,
not paralyzed by a preliminary vivisection, endowed with all her normal
vitality, lets him have his way, lets herself be sucked dry, with the
utmost apathy. Not a tremor in her outraged flesh, not a quiver of
resistance. No corpse could show greater indifference to the bite which
it receives.
Ah, but the maggot has chosen the hour of attack with traitorous
cunning! Had it appeared upon the scene earlier, when the larva was
consuming its store of honey, things of a surety would have gone badly
with it. The assaulted one, feeling herself bled to death by that
ravenous kiss, would have protested with much wriggling of body and
grinding of mandibles. The position would have ceased to be tenable
and the intruder would have perished. But at this hour all danger has
disappeared. Enclosed in its silken tent, the larva is seized with the
lethargy that precedes the metamorphosis. Its condition is not death,
but neither is it life. It is an intermediary condition; it is almost
the latent vitality of grain or egg. Therefore there is no sign of
irritation on the larva's part under the needle with which I stir it and
still less under the sucker of the Anthrax grub, which is able to drain
the affluent breast in perfect safety.
This lack of resistance, induced by the torpor of the transformation,
appears to me necessary, in view of the weakness of the nursling as it
leaves the egg, whenever the mother is herself incapable of depriving
the victim of the power of self defense. And so the nonparalyzed larvae
are attacked during the period of the nymphosis. We shall soon see other
instances of this.
Motionless though it be, the Chalicodoma grub is none the less alive.
The primrose tint and the glossy skin are unequivocal signs of health:
Were it really dead, it would, in less than twenty-four hours, turn a
dirty brown and, soon after, decompose into a fluid putrescence. Now
here is the marvelous thing: during the fortnight, roughly, that the
Anthrax' meal lasts, the butter color of the larva, an unfailing symptom
of the presence of life, continues unaltered and does not change into
brown, the sign of putrefaction, until hardly anything remains; and even
then the brown hue is often absent. As a rule, the look of live flesh is
preserved until the final pellet, formed of the skin, the sole residue,
makes its appearance. This pellet is white, with not a speck of tainted
matter, proving that life persists until the body is reduced to nothing.
We here witness the transfusion of one animal into another, the change
of Chalicodoma substance into Anthrax substance; and, as long as the
transfusion is not complete, as long as the eaten has not disappeared
altogether and become the eater, the ruined organism fights against
destruction. What manner of life is this, which may be compared with
the life of a night light whose extinction is not accomplished until
the last drop of oil has burnt away? How is any creature able to fight
against the final tragedy of corruption up to the last moment in which a
nucleus of matter remains as the seat of vital energy? The forces of the
living creature are here dissipated not through any disturbance of
the equilibrium of those forces, but for the want of any point of
application for them: the larva dies because materially there is no more
of it.
Can we be in the presence of the diffusive life of the plant, a life
which persists in a fragment? By no means: the grub is a more delicate
organic structure. There is unity between the several parts; and none of
them can be jeopardized without involving the ruin of the others. If I
myself give the larva a wound, if I bruise it, the whole body very soon
turns brown and begins to rot. It dies and decomposes by the mere prick
of a needle; it keeps alive, or at least preserves the freshness of
the live tissues, so long as it is not entirely emptied by the Anthrax'
sucker. A nothing kills it; an atrocious wasting does not. No, I fail to
understand the problem; and I bequeath it to others.
All that I can see by way of a glimpse--and even then I put forward my
suspicions with extreme reserve--all that I am permitted to surmise is
reduced to this: the substance of the sleeping larva as yet has no very
definite static existence; it is like the raw materials collected for a
building; it is waiting for the elaboration that is to make a bee of it.
To mould those shapeless lumps of the future insect, the air, that prime
adjuster of living things, circulates among them, passing through a
network of ducts. To organize them, to direct the placing of them, the
nervous system, the embryo of the animal, distributes its ramifications
over them. Nerve and air duct, therefore, are the essentials; the rest
is so much material in reserve for the process of the metamorphosis. As
long as that material is not employed, as long as it has not acquired
its final equilibrium, it can grow less and less; and life, though
languishing, will continue all the same on the express condition that
the respiratory organs and the nervous filaments be respected. It is as
it were the flame of the lamp, which, whether full or empty, continues
to give light so long as the wick is soaked in oil. Nothing but fluids,
the plastic materials held in reserve, can be distilled by the
Anthrax' sucker through the unpierced skin of the grub; no part of the
respiratory and nervous systems passes. As the two essential functions
remain unscathed, life goes on until exhaustion is completed. On the
other hand, if I myself injure the larva, I disturb the nervous or air
conducting filaments; and the bruised part spreads a taint, followed by
putrefaction, all over the body.
I have elsewhere, speaking of the Scolia [a digger wasp] devouring the
Cetonia grub, enlarged upon this refined art of eating which consists
in consuming the prey while killing it only at the last mouthfuls. The
Anthrax has the same requirements as his competitors who dine off fresh
viands. He needs meat of that day, taken from a single joint that has to
last a fortnight without going bad. His method of consuming reaches the
highest level of art: he does not cut into his prey, he sips it little
by little through his sucker. In this way, any dangerous risk is
averted. Whether he imbibe at this spot or at that, even if he abandon
the sucking process and resume it later, by no accident can he ever
attack that which it is incumbent upon him to respect lest corruption
supervene. The others have a fixed position on the victim, a place at
which their mandibles have to bite and enter. If they move away from
it, if they miss the appointed path, they imperil their existence. The
Anthrax, more highly favored, puts his mouth where it suits him; he
leaves off when he pleases and when he pleases starts again.
Unless I labor under a delusion, I think that I see the necessity for
this privilege. The egg of the carnivorous burrower is firmly fixed on
the victim at a point which varies considerably, it is true, according
to the nature of the prey, but which is uniform for the same species
of prey; moreover--and this is an important condition--the point of
adhesion of that egg is always the head, whereas the egg of a bee, of
the Osmia, for instance, is fixed to the mess of honey by the hinder
end. When hatched, the new born Wasp grub has not to choose for itself,
at its risk and peril, the suitable point at which to take the first cut
in the quarry without fear of killing it too quickly: all that it need
do is to bite at the spot where it has just been born. The mother, with
her unfailing instinct, has already made the dangerous choice; she has
stuck her egg on the propitious spot and, by the very act of doing so,
marked out the course for the inexperienced grub to follow. The tact of
ripe age here guides the young larva's behavior at table.
The conditions are very different in the Anthrax' case. The egg is not
placed upon the victuals, it is not even laid in the mason bee's cell.
This is the natural consequence of the mother's feeble frame and of her
lack of any instrument, such as a probe or auger, capable of piercing
the mortar wall. It is for the newly hatched grub to make its own way
into the dwelling. It enters, finds itself in the presence of ample
provisions, the larva of the mason bee. Free of its actions, it is at
liberty to attack the prey where it chooses; or rather the attacking
point will be decided at haphazard by the first contact of the mouth
in quest of food. Grant this mouth a set of carving tools, jaws and
mandibles; in short, suppose the grub of the Fly to possess a manner of
eating similar to that of the other carnivorous larvae; and the nursling
is at once threatened with a speedy death. He will split open his
nurse's belly, he will dig without any rule to guide him, he will bite
at random, essentials as well as accessories; and, from one day to the
next, he will set up gangrene in the violated mass, even as I myself do
when I give it a wound. For the lack of an attacking point prescribed
for him at birth, he will perish on the damaged provisions. His freedom
of action will have killed him.
Certainly, liberty is a noble attribute, even in an insignificant grub;
but it also has its dangers everywhere. The Anthrax escapes the peril
only on the condition of being, so to speak, muzzled. His mouth is not a
fierce forceps that tears asunder; it is a sucker that exhausts but does
not wound. Thus restrained by this safety appliance, which changes the
bite into a kiss, the grub has fresh victuals until it has finished
growing, although it knows nothing of the rules of methodical
consumption at a fixed point and in a predetermined direction.
The considerations which I have set forth seem to me strictly logical:
the Anthrax, owing to the very fact that he is free to take his
nourishment where he pleases on the body of the fostering larva, must,
for his own protection, be made incapable of opening his victim's body.
I am so utterly convinced of this harmonious relation between the eater
and the eaten that I do not hesitate to set it up as a principle. I
will therefore say this: whenever the egg of any kind of insect is not
fastened to the larva destined for its food, the young grub, free to
select the attacking point and to change it at will, is as it were
muzzled and consumes its provisions by a sort of suction, without
inflicting any appreciable wound. This restriction is essential to the
maintenance of the victuals in good condition. My principle is already
supported by examples many and various, whose depositions are all to the
same effect. The witnesses include, after the Anthrax, the Leucospis
[a parasitic insect] and his rivals, whose evidence we shall hear
presently; the Ephialtes mediator [an Ichneumon fly], who feeds, in
the dry brambles, on the larva of the Black Psen [a digger wasp]; the
Myodites, that strange, fly-shaped beetle whose grub consumes the larva
of the cockchafer. All--flies, ichneumon flies and beetles--scrupulously
spare their foster mother; they are careful not to tear her skin, so
that the vessel may keep its liquid good to the last.
The wholesomeness of the victuals is not the only condition imposed:
I find a second, which is no less essential. The substance of the
fostering larva must be sufficiently fluid to ooze through the unbroken
skin under the action of the sucker. Well, the necessary fluidity is
realized as the time of the metamorphosis draws near. When they wished
Medea to restore Pelias to the vigor of youth, his daughters cut the old
king's body to pieces and boiled it in a cauldron, for there can be no
new existence without a prior dissolution. We must pull down before
we can rebuild; the analysis of death is the first step towards the
synthesis of life. The substance of the grub that is to be transformed
into a bee begins, therefore, by disintegrating and dissolving into
a fluid broth. The materials of the future insect are obtained by a
general recasting. Even as the founder puts his old bronzes into the
melting pot in order afterwards to cast them in a mould whence the metal
will issue in a different shape, so life liquefies the grub, a mere
digesting machine, now thrown aside, and out of its running matter
produces the perfect insect, bee, butterfly or beetle, the final
manifestation of the living creature.
Let us open a Chalicodoma grub under the microscope, during the period
of torpor. Its contents consists almost entirely of a liquid broth, in
which swim numberless oily globules and a fine dust of uric acid, a sort
of off-throw of the oxidized tissues. A flowing thing, shapeless and
nameless, is all that the animal is, if we add abundant ramified air
ducts, some nervous filaments and, under the skin, a thin layer
of muscular fibers. A condition of this kind accounts for a fatty
transpiration through the skin when the Anthrax' sucker is at work. At
any other time, when the larva is in the active period or else when the
insect has reached the perfect stage, the firmness of the tissues would
resist the transfusion and the suckling of the Anthrax would become a
difficult matter, or even impossible. In point of fact, I find the grub
of the fly established, in the vast majority of cases, on the sleeping
larva and sometimes, but rarely, on the pupa. Never do I see it on the
vigorous larva eating its honey; and hardly ever on the insect brought
to perfection, as we find it enclosed in its cell all through the autumn
and winter. And we can say the same of the other grub eaters that drain
their victims without wounding them: all are engaged in their death
dealing work during the period of torpor, when the tissues are
fluidified. They empty their patient, who has become a bag of running
grease with a diffused life; but not one, among those I know, reaches
the Anthrax' perfection in the art of extraction.
Nor can any be compared with the Anthrax as regards the means brought
into play in order to leave the cell. These others, when they become
perfect insects, have implements for sapping and demolishing, stout
mandibles, capable of digging the ground, of pulling down clay partition
walls and even of reducing the mason bee's tough cement to powder. The
Anthrax, in her final form, has nothing like this. Her mouth is a short,
soft proboscis, good at most for soberly licking the sugary exudations
of the flowers; her slim legs are so feeble that to move a grain of
sand were an excessive task for them, enough to strain every joint; her
great, stiff wings, which must remain full spread, do not allow her to
slip through a narrow passage; her delicate suit of downy velvet, from
which you take the bloom by merely breathing on it, could not withstand
the rough contact of the gallery of a mine. Unable herself to enter the
Mason bee's cell to lay her egg, she cannot leave it either, when the
time comes to free herself and appear in broad daylight in her wedding
dress. The larva, on its side, is powerless to prepare the way for
the coming flight. That buttery little cylinder, owning no tools but a
sucker so flimsy that it barely arrives at substance and so small that
it is almost a geometrical point, is even weaker than the adult insect,
which at least flies and walks. The Mason bee's cell represents to it
a granite cave. How to get out? The problem would be insoluble to those
two incapables, if nothing else played its part.
Among insects, the nymph, or pupa, the transition stage between the
larval and the adult form, is generally a striking picture of every
weakness of a budding organism. A sort of mummy tight bound in swaddling
clothes, motionless and impassive, it awaits the resurrection. Its
tender tissues flow in every direction; its limbs, transparent as
crystal, are held fixed in their place, along the side, lest a
movement should disturb the exquisite delicacy of the work in course
of accomplishment. Even so, to secure his recovery, is a broken boned
patient held captive in the surgeon's bandages. Absolute stillness is
necessary in both cases, lest they be crippled or even die.
Well, here, by a strange inversion that confuses all our views on life,
a Cyclopean task is laid upon the nymph of the Anthrax. It is the nymph
that has to toil, to strive, to exhaust itself in efforts to burst the
wall and open the way out. To the embryo falls the desperate duty, which
shows no mercy to the nascent flesh; to the adult insect the joy of
resting in the sun. This transposition of functions has as its result
a well sinker's equipment in the nymph, an eccentric, complicated
equipment which nothing suggested in the larva and which nothing recalls
in the perfect insect. The set of tools includes an assortment of
plowshares, gimlets, hooks and spears and of other implements that are
not found in our trades nor named in our dictionaries. Let us do our
best to describe the strange piercing gear.
In a fortnight at most, the Anthrax has consumed the Chalicodoma grub,
whereof naught remains but the skin, gathered into a white granule. By
the time that July is nearly over, it becomes rare to find any nurslings
left upon their nurses. From this period until the following May,
nothing fresh happens. The Anthrax retains its larval shape without any
appreciable change and lies motionless in the mason bee's cocoon, beside
the pellet remains. When the fine days of May arrive, the grub shrivels
and casts its skin and the nymph appears, fully clad in a stout,
reddish, horny hide.
The head is round and large, separated from the thorax by a strangulated
furrow, crowned on top and in front with a sort of diadem of six hard,
sharp, black spikes, arranged in a semicircle whose concave side faces
downward. These spikes decrease slightly in length from the summit to
the ends of the arch. Taken together, they suggest the radial crowns
which we see the Roman emperors of the Decadence wear on the medals.
This six-fold plowshare is the chief excavating tool. Lower down, on the
median line, the instrument is finished off with a separate group of two
small black spikes, placed close together.
The thorax is smooth, the wing cases large, folded under the body like
a scarf and coming almost to the middle of the abdomen. This has nine
segments, of which four, starting with the second, are armed, on the
back, down the middle, with a belt of little horny arches, pale brown in
color, drawn up parallel to one another, set in the skin by their
convex surfaces and finishing at both ends with a hard, black point.
Altogether, the belt thus forms a double row of little thorns, with a
hollow in between. I count about twenty-five twin-toothed arches to one
segment, which gives a total of two hundred spikes for the four rings
thus armed.
The use of this rasp, or grater, is obvious: it gives the nymph a
purchase on the wall of its gallery as the work proceeds. Thus anchored
on a host of points, the stern pioneer is able to hit the obstacle
harder with its diadem of awls. Moreover, to make it more difficult for
the instrument to recoil, long, stiff bristles, pointing backwards,
are scattered here and there among the climbing belts. There are some
besides on the other segments, both on the ventral and the dorsal
surface. On the flanks, they are thicker and arranged as it were in
clusters.
The sixth segment carries a similar belt, but a much less powerful one,
consisting of a single row of unassuming thorns. The belt is weaker
still on the seventh segment; lastly, on the eighth, it is reduced to a
mere rough brown shading. Commencing with the sixth, the rings decrease
in width and the abdomen ends in a cone, the extremity of which, formed
of the ninth segment, constitutes a weapon of a new kind. It is a sheaf
of eight brown spikes. The last two exceed the others in length and
stand out from the group in a double terminal plowshare.
There is a round air hole in front, on either side of the thorax, and
similar stigmata on the flanks of each of the first seven abdominal
segments. When at rest, the nymph is curved into a bow. When about to
act, it suddenly unbends and straightens itself. It measures 15 to 20
millimeters long and 4 to 5 millimeters across.
Such is the strange perforating machine that is to prepare an outlet
for the feeble Anthrax through the Mason bee's cement. The structural
details, so difficult to explain in words, may be summed up as follows:
in front, on the forehead, a diadem of spikes, the ramming and digging
tool; behind, a many bladed plowshare which fits into a socket and
allows the pupa to slacken suddenly in readiness for an attack on the
barrier which has to be demolished; on the back, four climbing belts, or
graters, which keep the animal in position by biting on the walls of the
tunnel with their hundreds of teeth; and, all over the body, long, stiff
bristles, pointing backwards, to prevent falls or recoils.
A similar structure exists in the other species of Anthrax with slight
variations of detail. I will confine myself to one instance, that of
Anthrax sinuata, who thrives at the cost of Osmia tricornis. Her nymph
differs from that of Anthrax trifasciata, the Anthrax of the mason bee,
in possessing less powerful armor. Its four climbing belts consist of
only fifteen to seventeen double spiked arches, instead of twenty-five;
also, the abdominal segments, from the sixth onwards, are supplied
merely with stiff bristles, without a trace of horny spikes. If the
evolution of the various Anthrax flies were better known to us,
the number of these arches would, I believe, be of great service
to entomology in the differentiation of species. I see it remaining
constant for any given species, with marked variations between one
species and another. But this is not my business: I merely call the
attention of the classifiers to this field of study and pass on.
About the end of May, the coloring of the nymph, hitherto a light red,
alters greatly and forecasts the coming transformation. The head, the
thorax and the scarf formed by the wings become a handsome, shiny black.
A dark band shows on the back of the four segments with their two rows
of spikes; three spots appear on the two next rings; the anal armor
becomes darker. In this manner we foresee the black livery of the coming
insect. The time has arrived for the pupa to work at the exit gallery.
I was anxious to see it in action, not under natural conditions, which
would be impracticable, but in a glass tube in which I confine it
between two thick stoppers of sorghum pith. The space thus marked off
is about the same size as the natal cell. The partitions front and back,
although not so stout as the Chalicodoma's masonry, are nevertheless
firm enough not to yield except to prolonged efforts; on the other hand,
the side walls are smooth and the toothed belts will not be able to grip
them: a most unfavorable condition for the worker. No matter: in the
space of a single day, the pupa pierces the front partition, three
quarters of an inch thick. I see it fixing its double plowshare against
the back partition, arching into a bow and then suddenly releasing
itself and striking the plug in front of it with its barbed forehead.
Under the impact of the spikes, the sorghum slowly crumbles to pieces.
It is slow in coming away; but it comes away all the same, atom by atom.
At long intervals, the method changes. With its crown of awls driven
into the pith, the animal frets and fidgets, sways on the pivot of its
anal armor. The work of the auger follows that of the pickaxe. Then the
blows recommence, interspersed with periods of rest to recover from the
fatigue. At last, the hole is made. The pupa slips into it, but does not
pass through entirely: the head and thorax appear outside; the abdomen
remains held in the gallery.
The glass cell, with its lack of supports at the side, has certainly
perplexed my subject, which does not seem to have made use of all its
methods. The hole through the sorghum is wide and irregular; it is
a clumsy breach and not a gallery. When made through the mason bee's
walls, it is cylindrical, fairly neat and exactly of the animal's
diameter. So I hope that, under natural conditions, the pupa does not
give quite so many blows with the pickaxe and prefers to work with the
drill.
Narrowness and evenness in the exit tunnel are necessary to it. It
always remains half caught in it and even pretty securely fixed by the
graters on its back. Only the head and thorax emerge into the outer air.
This is a last precaution for the final deliverance. A fixed support is,
in fact, indispensable to the Anthrax for issuing from her horny sheath,
unfurling her great wings and extricating her slender legs from their
scabbards. All this very delicate work would be endangered by any lack
of steadiness.
The pupa, therefore, remains fixed by the graters of its back in the
narrow exit gallery and thus supplies the stable equilibrium essential
to the new birth. All is ready. It is time now for the great act. A
transversal cleft makes its appearance on the forehead, at the bottom
of the perforating diadem; a second, but longitudinal slit divides the
skull in two and extends down the thorax. Through this cross-shaped
opening, the Anthrax suddenly appears, all moist with the humors of
life's laboratory. She steadies herself upon her trembling legs, dries
her wings and takes to flight, leaving at the window of the cell
her nymphal slough, which keeps intact for a very long period. The
sand-colored fly has five or six weeks before her, wherein to explore
the clay nests amid the thyme and to take her small share of the joys
of life. In July, we shall see her once more, busy this time with the
entrance into the cell, which is even stranger than the exit.