THE PRIMARY LARVA OF THE SITARES
Nothing new happens before the end of the following April. I shall
profit by this long period of repose to tell you more about the young
larva, of which I will begin by giving a description. Its length is a
twenty-fifth of an inch, or a little less. It is hard as leather, a
glossy greenish black, convex above and flat below, long and slender,
with a diameter increasing gradually from the head to the hinder
extremity of the metathorax, after which it rapidly diminishes. Its
head is a trifle longer than it is wide and is slightly dilated at the
base; it is pale-red near the mouth and darker about the ocelli.
The labrum forms a segment of a circle; it is reddish, edged with a
small number of very short, stiff hairs. The mandibles are powerful,
red-brown, curved and sharp; when at rest they meet without crossing.
The maxillary palpi are rather long, consisting of two cylindrical
sections of equal length, the outer ending in a very short bristle.
The jaws and the lower lip are not sufficiently visible to lend
themselves to accurate description.
The antennae consist of two cylindrical segments, equal in length, not
very definitely divided; these segments are nearly as long as those of
the palpi; the outer is surmounted by a cirrus whose length is as much
as thrice that of the head and tapers off until it becomes invisible
under a powerful pocket-lens. Behind the base of either antennae are
two ocelli, unequal in size and almost touching.
The thoracic segments are of equal length and increase gradually in
width from front to back. The prothorax is wider than the head, but is
narrower in front than at the base and is slightly rounded at the
sides. The legs are of medium length and fairly robust, ending in a
long, powerful, sharp and very mobile claw. On the haunch and thigh of
each leg is a long cirrus, like that of the antennae, almost as long
as the whole limb and standing at right angles to the plane of
locomotion when the creature moves. There are a few stiff bristles on
the legs.
The abdomen has nine segments, of practically equal length, but
shorter than those of the thorax and diminishing very rapidly in width
toward the last. Fixed below the eighth segment, or rather below the
strip of membrane separating this segment and the last, we see two
spikes, slightly curved, short, but with strong, sharp, hard points,
and placed one to the right and the other to the left of the median
line. These two appendages are able, by means of a mechanism
recalling, on a smaller scale, that of the Snail's horns, to withdraw
into themselves, as a result of the membranous character of their
base. They can also retreat under the eighth segment, borne, as they
are, by the anal segment, when this last, as it contracts, withdraws
into the eighth. Lastly, the ninth or anal segment bears on its hinder
edge two long cirri, like those of the legs and the antennae, curving
backwards from tip to base. At the rear of this segment a fleshy
nipple appears, more or less prominent; this is the anus. I do not
know where the stigmata are placed; they have evaded my
investigations, though these were undertaken with the aid of the
microscope.
When the larva is at rest, the various segments overlap evenly; and
the membranous intervals, corresponding with the articulations, do not
show. But, when the larva walks, all the articulations, especially
those of the abdominal segments, are distended and end by occupying
almost as much space as the horny arches. At the same time the anal
segment emerges from the sheath formed by the eighth; the anus, in
turn, is stretched into a nipple; and the two points of the
penultimate ring rise, at first slowly, and then suddenly stand up
with an abrupt motion similar to that of a spring when released. In
the end, these two points diverge like the horns of a crescent. Once
this complex apparatus is unfolded, the tiny creature is ready to
crawl upon the most slippery surface.
The last segment and its anal button are curved at right angles to the
axis of the body; and the anus comes and presses upon the surface of
locomotion, where it ejects a tiny drop of transparent, treacly fluid,
which glues and holds the little creature firmly in position,
supported on a sort of tripod formed by the anal button and the two
cirri of the last segment. If we are observing the animal's manner of
locomotion on a strip of glass, we can hold the strip in a vertical
position, or even turn it upside down, or shake it lightly, without
causing the larva to become detached and fall, held fast as it is by
the glutinous secretion of the anal button.
If it has to proceed along a surface where there is no danger of a
fall, the microscopic creature employs another method. It crooks its
belly and, when the two spikes of the eighth segment, now fully
outspread, have found a firm support by ploughing, so to speak, the
surface of locomotion, it bears upon that base and pushes forward by
expanding the various abdominal articulations. This forward movement
is also assisted by the action of the legs, which are far from
remaining inactive. This done, it casts anchor with the powerful claws
of its feet; the abdomen contracts; the various segments draw
together; and the anus, pulled forward, obtains a fresh purchase, with
the aid of the two spikes, before beginning the second of these
curious strides.
During these manoeuvres, the cirri of the flanks and thighs drag along
the supporting surface and by their length and elasticity appear
fitted only to impede progress. But let us not be in a hurry to
conclude that we have discovered an inconsistency: the least of
creatures is adapted to the conditions amid which it has to live;
there is reason to believe that these filaments, far from hampering
the pigmy's progress, must, in normal circumstances, be of some
assistance to it.
Even the little that we have just learnt shows us that the young
Sitaris-larva is not called upon to move on an ordinary surface. The
spot, whatever it may be like, where this larva is to live later
exposes it to the risk of many dangerous falls, since, in order to
prevent them, it is not only equipped with strong and extremely mobile
talons and a steel-shod crescent, a sort of ploughshare capable of
biting into the most highly polished substance, but is further
provided with a viscous liquid, sufficiently tenacious and adhesive to
hold it in position without the help of other appliances. In vain I
racked my brains to guess what the substance might be, so shifting, so
uncertain and so perilous, which the young Sitares are destined to
inhabit; and I discovered nothing to explain the necessity for the
structure which I have described. Convinced beforehand, by an
attentive examination of this structure, that I should witness some
peculiar habits, I waited with eager impatience for the return of the
warm weather, never doubting that by dint of persevering observation
the mystery would be disclosed to me next spring. At last this spring,
so fervently desired, arrived; I brought to bear all the patience, all
the imagination, all the insight and discernment that I may possess;
but, to my utter shame and still greater regret, the secret escaped
me. Oh, how painful are those tortures of indecision, when one has to
postpone till the following year an investigation which has led to no
result!
My observations made during the spring of 1856, although purely
negative, nevertheless have an interest of their own, because they
prove the inaccuracy of certain suppositions to which the undeniable
parasitism of the Sitares naturally inclines us. I will therefore
relate them in a few words. At the end of April, the young larvae,
hitherto motionless and concealed in the spongy heap of the egg-skins,
emerge from their immobility, scatter and run about in all directions
through the boxes and jars in which they have passed the winter. By
their hurried gait and their indefatigable evolutions we readily guess
that they are seeking something which they lack. What can this
something be, unless it be food? For remember that these larvae were
hatched at the end of September and that since then, that is to say,
for seven long months, they have taken no nourishment, though they
have spent this period in the full enjoyment of their vitality, as I
was able to assure myself all through the winter by irritating them,
and not in a state of torpor similar to that of the hibernating
animals. From the moment of their hatching they are doomed, although
full of life, to an absolute abstinence of seven months' duration; and
it is natural to suppose, when we see their present excitement, that
an imperious hunger sets them bustling in this fashion.
The desired nourishment could only be the contents of the cells of the
Anthophora, since we afterwards find the Sitares in these cells. Now
these contents are limited to honey or larvae. It just happens that I
have kept some Anthophora-cells occupied by larvae or nymphs. I place
a few of these, some open, some closed, within reach of the young
Sitares, as I had already done directly after the hatching. I even
slip the Sitares into the cells: I place them on the sides of the
larva, a succulent morsel to all appearances; I do all sorts of things
to tempt their appetite; and, after exhausting my ingenuity, which
continues fruitless, I remain convinced that my famished grubs are
seeking neither the larvae nor nymphs of the Anthophora.
Let us now try honey. We must obviously employ honey prepared by the
same species of Anthophora as that at whose cost the Sitares live. But
this Bee is not very common in the neighbourhood of Avignon; and my
engagements at the college[1] do not allow me to absent myself for the
purpose of repairing to Carpentras, where she is so abundant. In
hunting for cells provisioned with honey I thus lose a good part of
the month of May; however, I end by finding some which are newly
sealed and which belong to the right Anthophora. I open these cells
with the feverish impatience of a sorely-tried longing. All goes well:
they are half-full of fluid, dark, nauseating honey, with the Bee's
lately-hatched larva floating on the surface. This larva is removed;
and taking a thousand precautions, I lay one or more Sitares on the
surface of the honey. In other cells I leave the Bee's larva and
insert Sitares, placing them sometimes on the honey and sometimes on
the inner wall of the cell or simply at the entrance. Lastly, all the
cells thus prepared are put in glass tubes, which enable me to observe
them readily, without fear of disturbing my famished guests at their
meal.
[Footnote 1: Fabre, as a young man, was a master at Avignon College.
Cf. _The Life of the Fly_: chaps. xii., xiii., xix. and
xx.--_Translator's Note_.]
But what am I saying? Their meal? There is no meal! The Sitares,
placed at the entrance to a cell, far from seeking to make their way
in, leave it and go roaming about the glass tube; those which have
been placed on the inner surface of the cells, near the honey, emerge
precipitately, half-caught in the glue and tripping at every step;
lastly, those which I thought I had favoured the most, by placing them
on the honey itself, struggle, become entangled in the sticky mass and
perish in it, suffocated. Never did experiment break down so
completely! Larvae, nymphs, cells, honey: I have offered you them all!
Then what do you want, you fiendish little creatures?
Tired of all these fruitless attempts, I ended where I ought to have
begun: I went to Carpentras. But it was too late: the Anthophora had
finished her work; and I did not succeed in seeing anything new.
During the course of the year I learnt from Leon Dufour,[2] to whom I
had spoken of the Sitares, that the tiny creature which he had found
on the Andrenae[3] and described under the generic name of
Triungulinus, was recognized later by Newport[4] as the larva of a
Meloe, or Oil-beetle. Now it so happened that I had found a few
Oil-beetles in the cells of the same Anthophora that nourishes the
Sitares. Could there be a similarity of habits between the two kinds
of insects? This idea threw a sudden light for me upon the subject;
but I had plenty of time in which to mature my plans: I had another
year to wait.
[Footnote 2: Jean Marie Leon Dufour (1780-1865), an army surgeon who
served with distinction in several campaigns, and subsequently
practised as a doctor in the Landes, where he attained great eminence
as a naturalist. Fabre often refers to him as the Wizard of the
Landes. Cf. _The Life of the Spider_, by J. Henri Fabre, translated by
Alexander Teixeira de Mattos: chap. i.; and _The Life of the Fly_:
chap. i.--_Translator's Note_.]
[Footnote 3: A genus of Burrowing Bee, the most numerous in species
among the British Bees.--_Translator's Note_.]
[Footnote 4: George Newport (1803-1854), an English surgeon and
naturalist, president of the Entomological Society from 1844 to 1845
and an expert in insect anatomy.--_Translator's Note_.]
When April came, my Sitaris-larvae began, as usual, to bestir
themselves. The first Bee to appear, an Osmia, is dropped alive into a
glass jar containing a few of these larvae; and after a lapse of some
fifteen minutes I inspect them through the pocket-lens. Five Sitares
are embedded in the fleece of the thorax. It is done, the problem's
solved! The larvae of the Sitares, like those of the Oil-beetles,
cling like grim death to the fleece of their generous host and make
him carry them into the cell. Ten times over I repeat the experiment
with the various Bees that come to plunder the lilac flowering outside
my window and in particular with male Anthophorae; the result is still
the same: the larvae embed themselves in the hair of the Bees' thorax.
But after so many disappointments one becomes distrustful and it is
better to go and observe the facts upon the spot; besides, the Easter
holidays fall very conveniently and afford me the leisure for my
observations.
I will admit that my heart was beating a little faster than usual when
I found myself once again standing in front of the perpendicular bank
in which the Anthophora nests. What will be the result of the
experiment? Will it once more cover me with confusion? The weather is
cold and rainy; not a Bee shows herself on the few spring flowers that
have come out. Numbers of Anthophorae cower, numbed and motionless, at
the entrance to the galleries. With the tweezers, I extract them one
by one from their lurking-places, to examine them under the lens. The
first has Sitaris-larvae on her thorax; so has the second; the third
and fourth likewise; and so on, as far as I care to pursue the
examination. I change galleries ten times, twenty times; the result is
invariable. Then, for me, occurred one of the moments which come to
those who, after considering and reconsidering an idea for years and
years from every point of view, are at last able to cry: "Eureka!"
On the days that followed, a serene and balmy sky enabled the
Anthophorae to leave their retreats and scatter over the countryside
and despoil the flowers. I renewed my examination on those Anthophorae
flying incessantly from one flower to another, whether in the
neighbourhood of the places where they were born or at great distances
from these places. Some were without Sitaris-larvae; others, more
numerous, had two, three, four, five or more among the hairs of their
thorax. At Avignon, where I have not yet seen _Sitaris humeralis_, the
same species of Anthophora, observed at almost the same season, while
pillaging the lilac-blossom, was always free of young Sitaris-grubs;
at Carpentras, on the contrary, where there is not a single
Anthophora-colony without Sitares, nearly three-quarters of the
specimens which I examined carried a few of these larvae in their
fleece.
But, on the other hand, if we look for these larvae in the
entrance-lobbies where we found them, a few days ago, piled up in
heaps, we no longer see them. Consequently, when the Anthophorae,
having opened their cells, enter the galleries to reach the exit and
fly away, or else when the bad weather and the darkness bring them
back there for a time, the young Sitaris-larvae, kept on the alert in
these same galleries by the stimulus of instinct, attach themselves to
the Bees, wriggling into their fur and clutching it so firmly that
they need not fear a fall during the long journeys of the insect which
carries them. By thus attaching themselves to the Anthophorae the
young Sitares evidently intend to get themselves carried, at the
opportune moment, into the victualled cells.
One might even at first sight believe that they live for some time on
the Anthophora's body, just as the ordinary parasites, the various
species of Lice, live on the body of the animal that feeds them. But
not at all. The young Sitares, embedded in the fleece, at right angles
to the Anthophora's body, head inwards, rump outwards, do not stir
from the point which they have selected, a point near the Bee's
shoulders. We do not see them wandering from spot to spot, exploring
the Anthophora's body, seeking the part where the skin is more
delicate, as they would certainly do if they were really deriving some
nourishment from the juices of the Bee. On the contrary, they are
nearly always established on the toughest and hardest part of the
Bee's body, on the thorax, a little below the insertion of the wings,
or, more rarely, on the head; and they remain absolutely motionless,
fixed to the same hair, by means of the mandibles, the feet, the
closed crescent of the eighth segment and, lastly, the glue of the
anal button. If they chance to be disturbed in this position, they
reluctantly repair to another point of the thorax, pushing their way
through the insect's fur and in the end fastening on to another hair,
as before.
To confirm my conviction that the young Sitaris-grubs do not feed on
the Anthophora's body, I have sometimes placed within their reach, in
a glass jar, some Bees that have long been dead and are completely
dried up. On these dry corpses, fit at most for gnawing, but certainly
containing nothing to suck, the Sitaris-larvae took up their customary
position and there remained motionless as on the living insect. They
obtain nothing, therefore, from the Anthophora's body; but perhaps
they nibble her fleece, even as the Bird-lice nibble the birds'
feathers?
To do this, they would require mouth-parts endowed with a certain
strength and, in particular, horny and sturdy jaws, whereas their jaws
are so fine that a microscopic examination failed to show them to me.
The larvae, it is true, are provided with powerful mandibles; but
these finely-pointed mandibles, with their backward curve, though
excellent for tugging at food and tearing it to pieces, are useless
for grinding it or gnawing it. Lastly, we have a final proof of the
passive condition of the Sitaris-larvae on the body of the Anthophorae
in the fact that the Bees do not appear to be in any way incommoded by
their presence, since we do not see them trying to rid themselves of
the grubs. Some Anthophorae which were free from these grubs and some
others which were carrying five or six upon their bodies were placed
separately in glass jars. When the first disturbance resulting from
their captivity was appeased, I could see nothing peculiar about those
occupied by the young Sitares. And, if all these arguments were not
sufficient, I might add that a creature which has already been able to
spend seven months without food and which in a few days' time will
proceed to drink a highly-flavoured fluid would be guilty of a
singular inconsistency if it were to start nibbling the dry fleece of
a Bee. It therefore seems to me undeniable that the young Sitares
settle on the Anthophora's body merely to make her carry them into the
cells which she will soon be building.
But until then the future parasites must hold tight to the fleece of
their hostess, despite her rapid evolutions among the flowers, despite
her rubbing against the walls of the galleries when she enters to take
shelter and, above all, despite the brushing which she must often give
herself with her feet to dust herself and keep spick and span. Hence
no doubt the need for that curious apparatus which no standing or
moving upon ordinary surfaces could explain, as was said above, when
we were wondering what the shifting, swaying, dangerous body might be
on which the larva would have to establish itself later. This body is
a hair of a Bee who makes a thousand rapid journeys, now diving into
her narrow galleries, now forcing her way down the tight throat of a
corolla, and who never rests except to brush herself with her feet and
remove the specks of dust collected by the down which covers her.
We can now easily understand the use of the projecting crescent whose
two horns, by closing together, are able to take hold of a hair more
easily than the most delicate tweezers; we perceive the full value of
the tenacious adhesive provided by the anus to save the tiny creature,
at the least sign of danger, from an imminent fall; we realize lastly
the useful function that may be fulfilled by the elastic cirri of the
flanks and legs, which are an absolute and most embarrassing
superfluity when walking upon a smooth surface, but which, in the
present case, penetrate like so many probes into the thickness of the
Anthophora's down and serve as it were to anchor the Sitaris-larva in
position. The more we consider this arrangement, which seems modelled
by a blind caprice so long as the grub drags itself laboriously over a
smooth surface, the more do we marvel at the means, as effective as
they are varied, which are lavished upon this fragile creature to help
it to preserve its unstable equilibrium.
Before I describe what becomes of the Sitaris-grubs on leaving the
body of the Anthophorae, I must not omit to mention one very
remarkable peculiarity. All the Bees invaded by these grubs that have
hitherto been observed have, without one exception, been male
Anthophorae. Those whom I drew from their lurking-places were males;
those whom I caught upon the flowers were males; and, in spite of the
most active search, I failed to find a single female at liberty. The
cause of this total absence of females is easy to understand.
If we remove a few clods from the area occupied by the nests, we see
that, though all the males have already opened and abandoned their
cells, the females, on the contrary, are still enclosed in theirs, but
on the point of soon taking flight. This appearance of the males
almost a month before the emergence of the females is not peculiar to
the Anthophorae; I have observed it in many other Bees and
particularly in the Three-horned Osmia (_O. tricornis_), who inhabits
the same site as the Hairy-footed Anthophora (_A. pilipes_). The males
of the Osmia make their appearance even before those of the Anthophora
and at so early a season that the young Sitaris-larvae are perhaps not
yet aroused by the instinctive impulse which urges them to activity.
It is no doubt to their precocious awakening that the males of the
Osmia owe their ability to traverse with impunity the corridors in
which the young Sitaris-grubs are heaped together, without having the
latter fasten to their fleece; at least, I cannot otherwise explain
the absence of these larvae from the backs of the male Osmiae, since,
when we place them artificially in the presence of these Bees, they
fasten on them as readily as on the Anthophorae.
The emergence from the common site begun by the male Osmiae is
continued by the male Anthophorae and ends with the almost
simultaneous emergence of the female Osmiae and Anthophorae. I was
easily able to verify this sequence by observing at my own place, in
the early spring, the dates at which the cells, collected during the
previous autumn, were broken.
At the moment of their emergence, the male Anthophorae, passing
through the galleries in which the Sitaris-larvae are waiting on the
alert, must pick up a certain number of them; and those among them
who, by entering empty corridors, escape the enemy on this first
occasion will not evade him for long, for the rain, the chilly air and
the darkness bring them back to their former homes, where they take
shelter now in one gallery, now in another, during a great part of
April. This constant traffic of the males in the entrance-lobbies of
their houses and the prolonged stay which the bad weather often
compels them to make provide the Sitares with the most favourable
opportunity for slipping into the Bees' fur and taking up their
position. Moreover, when this state of affairs has lasted a month or
so, there can be only very few if any larvae left wandering about
without having attained their end. At that period I was unable to find
them anywhere save on the body of the male Anthophora.
It is therefore extremely probable that, on their emergence, which
takes place as May draws near, the female Anthophorae do not pick up
Sitaris-larvae in the corridors, or pick up only a number which will
not compare with that carried by the males. In fact, the first females
that I was able to observe in April, in the actual neighbourhood of
the nests, were free from these larvae. Nevertheless it is upon the
females that the Sitaris-larvae must finally establish themselves, for
the males upon whom they now are cannot introduce them into the cells,
since they take no part in the building or provisioning. There is
therefore, at a given moment, a transfer of Sitaris-larvae from the
male Anthophorae to the females; and this transfer is, beyond a doubt,
effected during the union of the sexes. The female finds in the male's
embraces both life and death for her offspring; at the moment when she
surrenders herself to the male for the preservation of her race, the
vigilant parasites pass from the male to the female, with the
extermination of that same race in view.
In support of these deductions, here is a fairly conclusive
experiment, though it reproduces the natural circumstances but
roughly. On a female taken in her cell and therefore free from
Sitares, I place a male who is infested with them; and I keep the two
sexes in contact, suppressing their unruly movements as far as I am
able. After fifteen or twenty minutes of this enforced proximity, the
female is invaded by one or more of the larvae which at first were on
the male. True, experiment does not always succeed under these
imperfect conditions.
By watching at Avignon the few Anthophorae that I succeeded in
discovering, I was able to detect the precise moment of their work;
and on the following Thursday,[5] the 21st of May, I repaired in all
haste to Carpentras, to witness, if possible, the entrance of the
Sitares into the Bee's cells. I was not mistaken: the works were in
full swing.
[Footnote 5: Thursday is the weekly holiday in French
schools.--_Translator's Note_.]
In front of a high expanse of earth, a swarm stimulated by the sun,
which floods it with light and heat, is dancing a crazy ballet. It is
a hover of Anthophorae, a few feet thick and covering an area which
matches the sort of house-front formed by the perpendicular soil. From
the tumultuous heart of the cloud rises a monotonous, threatening
murmur, while the bewildered eye strays through the inextricable
evolutions of the eager throng. With the rapidity of a lightning-flash
thousands of Anthophorae are incessantly flying off and scattering
over the country-side in search of booty; thousands of others also are
incessantly arriving, laden with honey or mortar, and keeping up the
formidable proportions of the swarm.
I was at that time something of a novice as regards the nature of
these insects:
"Woe," said I to myself, "woe to the reckless wight bold enough to
enter the heart of this swarm and, above all, to lay a rash hand upon
the dwellings under construction! Forthwith surrounded by the furious
host, he would expiate his rash attempt, stabbed by a thousand
stings!"
At this thought, rendered still more alarming by the recollection of
certain misadventures of which I had been the victim when seeking to
observe too closely the combs of the Hornet (_Vespa crabro_), I felt a
shiver of apprehension pass through my body.
Yet, to obtain light upon the question which brings me hither, I must
needs penetrate the fearsome swarm; I must stand for whole hours,
perhaps all day, watching the works which I intend to upset; lens in
hand, I must scrutinize, unmoved amid the whirl, the things that are
happening in the cells. The use moreover of a mask, of gloves, of a
covering of any kind is impracticable, for utter dexterity of the
fingers and complete liberty of sight are essential to the
investigations which I have to make. No matter: even though I leave
this wasps'-nest with a face swollen beyond recognition, I must to-day
obtain a decisive solution of the problem which has preoccupied me too
long.
A few strokes of the net, aimed, beyond the limits of the swarm, at
the Anthophorae on their way to the harvest or returning, soon
informed me that the Sitaris-larvae are perched on the thorax, as I
expected, occupying the same position as on the males. The
circumstances therefore could not be more favourable. We will inspect
the cells without further delay.
My preparations are made at once: I button my clothes tightly, so as
to afford the Bees the least possible opportunity, and I enter the
heart of the swarm. A few blows of the mattock, which arouse a far
from reassuring crescendo in the humming of the Anthophorae, soon
place me in possession of a lump of earth; and I beat a hasty retreat,
greatly astonished to find myself still safe and sound and unpursued.
But the lump of earth which I have removed is from a part too near the
surface; it contains nothing but Osmia-cells, which do not interest me
for the moment. A second expedition is made, lasting longer than the
first; and, though my retreat is effected without great precipitation,
not an Anthophora has touched me with her sting, nor even shown
herself disposed to fall upon the aggressor.
This success emboldens me. I remain permanently in front of the work
in progress, continually removing lumps of earth filled with cells,
spilling the liquid honey on the ground, eviscerating larvae and
crushing the Bees busily occupied in their nests. All this devastation
results merely in arousing a louder hum in the swarm and is not
followed by any hostile demonstration. The Anthophorae whose cells are
not hurt go about their labours as if nothing unusual were happening
round about them; those whose dwellings are overturned try to repair
them, or hover distractedly in front of the ruins; but none of them
seems inclined to swoop down upon the author of the damage. At most, a
few, more irritated than the rest, come at intervals and hover before
my face, confronting me at a distance of a couple of inches, and then
fly away, after a few moments of this curious inspection.
Despite the selection of a common site for their nests, which might
suggest an attempt at communistic interests among the Anthophorae,
these Bees, therefore, obey the egotistical law of each one for
himself and do not know how to band themselves together to repel an
enemy who threatens one and all. Taken singly, the Anthophora does not
even know how to dash at the enemy who is ravaging her cells and drive
him away with her stings; the pacific creature hastily leaves its
dwelling when disturbed by undermining and escapes in a crippled
state, sometimes even mortally wounded, without thinking of making use
of its venomous sting, except when it is seized and handled. Many
other Hymenoptera, honey-gatherers or hunters, are quite as
spiritless; and I can assert to-day, after a long experience, that
only the Social Hymenoptera, the Hive-bees, the Common Wasps and the
Bumble-bees, know how to devise a common defence; and only they dare
fall singly upon the aggressor, to wreak an individual vengeance.
Thanks to this unexpected lack of spirit in the Mason-bee, I was able
for hours to pursue my investigations at my leisure, seated on a stone
in the midst of the murmuring and distracted swarm, without receiving
a single sting, though I took no precautions whatever. Country-folk,
happening to pass and beholding me seated, unperturbed, in the midst
of the whirl of Bees, stopped aghast to ask me whether I had bewitched
them, whether I charmed them, since I appeared to have nothing to fear
from them:
"_Me, moun bel ami, li-z-ave doun escounjurado que vous pougnioun pas,
caneu de sort!_"
My miscellaneous impedimenta spread over the ground, boxes, glass jars
and tubes, tweezers and magnifying-glasses, were certainly regarded by
these good people as the implements of my wizardry.
We will now proceed to examine the cells. Some are still open and
contain only a more or less complete store of honey. Others are
hermetically sealed with an earthen lid. The contents of these latter
vary greatly. Sometimes we find the larva of a Bee which has finished
its mess or is on the point of finishing it; sometimes a larva, white
like the first, but more corpulent and of a different shape; at other
times honey with an egg floating on the surface. The honey is liquid
and sticky, with a brownish colour and a very strong, repulsive smell.
The egg is of a beautiful white, cylindrical in shape, slightly curved
into an arc, a fifth or a sixth of an inch in length and not quite a
twenty-fifth of an inch in thickness; it is the egg of the Anthophora.
In a few cells this egg is floating all alone on the surface of the
honey; in others, very numerous these, we see, lying on the egg of the
Anthophora, as on a sort of raft, a young Sitaris-grub with the shape
and the dimensions which I have described above, that is to say, with
the shape and the dimensions which the creature possesses on leaving
the egg. This is the enemy within the gates.
When and how did it get in? In none of the cells where I have observed
it was I able to distinguish a fissure which could have allowed it to
enter; they are all sealed in a quite irreproachable manner. The
parasite therefore established itself in the honey-warehouse before
the warehouse was closed; on the other hand, the open cells, full of
honey, but as yet without the egg of the Anthophora, are always free
from parasites. It is therefore during the laying, or afterwards, when
the Anthophora is occupied in plastering the door of the cell, that
the young larva gains admittance. It is impossible to decide by
experiment to which of these two periods we must ascribe the
introduction of the Sitares into the cell; for, however peaceable the
Anthophora may be, it is evident that we cannot hope to witness what
happens in the cell at the moment when she is laying an egg or at the
moment when she is making the lid. But a few attempts will soon
convince us that the only second which would allow the Sitaris to
establish itself in the home of the Bee is the very second when the
egg is laid on the surface of the honey.
Let us take an Anthophora-cell full of honey and furnished with an egg
and, after removing the lid, place it in a glass tube with a few
Sitaris-grubs. The grubs do not appear at all eager for this wealth of
nectar placed within their reach; they wander at random about the
tube, run about the outside of the cell, sometimes happen upon the
edge of the orifice and very rarely venture inside. When they do, they
do not go far in and they come out again at once. If one happens to
reach the honey, which only half fills the cell, it tries to escape as
soon as it has perceived the shifting nature of the sticky soil upon
which it was about to enter; but, tottering at every step, because of
the viscous matter clinging to its feet, it often ends by falling back
into the honey, where it dies of suffocation.
Again, we may experiment as follows: having prepared a cell as before,
we place a larva most carefully on its inner wall, or else on the
surface of the food itself. In the first case, the larva hastens to
leave the cell; in the second case, it struggles awhile on the surface
of the honey and ends by getting so completely caught that, after a
thousand efforts to gain the shore, it is swallowed up in the viscous
lake.
In short, all attempts to establish the Sitaris-grub in an
Anthophora-cell provisioned with honey and furnished with an egg are
no more successful than those which I made with cells whose store of
food had already been broached by the larva of the Bee, as described
above. It is therefore certain that the Sitaris-grub does not leave
the fleece of the Mason-bee when the Bee is in her cell or at the
entrance to it, in order itself to make a rush for the coveted honey;
for this honey would inevitably cause its death, if it happened by
accident to touch the perilous surface merely with the tip of its
tarsi.
Since we cannot admit that the Sitaris-grub leaves the furry corselet
of its hostess to slip unseen into the cell, whose orifice is not yet
wholly walled up, at the moment when the Anthophora is building her
door, all that remains to investigate is the second at which the egg
is being laid. Remember in the first place that the young Sitaris
which we find in a closed cell is always placed on the egg of the Bee.
We shall see in a minute that this egg not merely serves as a raft for
the tiny creature floating on a very treacherous lake, but also
constitutes the first and indispensable part of its diet. To get at
this egg, situated in the centre of the lake of honey, to reach, at
all costs, this raft, which is also its first ration, the young larva
evidently possesses some means of avoiding the fatal contact of the
honey; and this means can be provided only by the actions of the Bee
herself.
In the second place, observations repeated _ad nauseam_ have shown me
that at no period do we find in each invaded cell more than a single
Sitaris, in one or other of the forms which it successively assumes.
Yet there are several young larvae established in the silky tangle of
the Bee's thorax, all eagerly watching for the propitious moment at
which to enter the dwelling in which they are to continue their
development. How then does it happen that these larvae, goaded by such
an appetite as one would expect after seven or eight months' complete
abstinence, instead of all rushing together into the first cell within
reach, on the contrary enter the various cells which the Bee is
provisioning one at a time and in perfect order? Some action must take
place here independent of the Sitares.
To satisfy those two indispensable conditions, the arrival of the
larva upon the egg without crossing the honey and the introduction of
a single larva among all those waiting in the fleece of the Bee, there
can be only one explanation, which is to suppose that, at the moment
when the Anthophora's egg is half out of the oviduct, one of the
Sitares which have hastened from the thorax to the tip of the abdomen,
one more highly favoured by its position, instantly settles upon the
egg, a bridge too narrow for two, and with it reaches the surface of
the honey. The impossibility of otherwise fulfilling the two
conditions which I have stated gives to the explanation which I am
offering a degree of certainty almost equivalent to that which would
be furnished by direct observation, which is here, unfortunately,
impracticable. This presupposes, it is true, in the microscopic little
creature destined to live in a place where so many dangers threaten it
from the first, an astonishingly rational inspiration, which adapts
the means to the end with amazing logic. But is not this the
invariable conclusion to which the study of instinct always leads us?
When dropping her egg upon the honey, therefore, the Anthophora at the
same time deposits in her cell the mortal enemy of her race; she
carefully plasters the lid which closes the entrance to the cell; and
all is done. A second cell is built beside it, probably to suffer the
same fatal doom; and so on until the more or less numerous parasites
sheltered by her down are all accommodated. Let us leave the unhappy
mother to continue her fruitless task and turn our attention to the
young larva which has so adroitly secured itself board and lodging.
In opening cells whose lid is still moist, we end by discovering one
in which the egg, recently laid, supports a young Sitaris. This egg is
intact and in irreproachable condition. But now the work of
devastation begins: the larva, a tiny black speck which we see running
over the white surface of the egg, at last stops and balances itself
firmly on its six legs; then, seizing the delicate skin of the egg
with the sharp hooks of its mandibles, it tugs at it violently until
it breaks, spilling its contents, which the larva eagerly drinks up.
Thus the first stroke of the mandibles which the parasite delivers in
the usurped cell is aimed at the destruction of the Bee's egg. A
highly logical precaution! The Sitaris-larva, as we shall see, has to
feed upon the honey in the cell; the Anthophora-larva which would
proceed from that egg would require the same food; but the portion is
too small for two; so, quick, a bite at the egg and the difficulty
will be removed. The story of these facts calls for no comment. This
destruction of the cumbersome egg is all the more inevitable inasmuch
as special tastes compel the young Sitaris-grub to make its first
meals of it. Indeed we see the tiny creature begin by greedily
drinking the juices which the torn wrapper of the egg allows to
escape; and for several days it may be observed, at one time
motionless on this envelope, in which it rummages at intervals with
its head, at others running over it from end to end to rip it open
still wider and to cause a little of the juices, which become daily
less abundant, to trickle from it; but we never catch it imbibing the
honey which surrounds it on every side.
For that matter, it is easy to convince ourselves that the egg
combines with the function of a life-buoy that of the first ration. I
have laid on the surface of the honey in a cell a tiny strip of paper,
of the same dimensions as the egg; and on this raft I have placed a
Sitaris-larva. Despite every care, my attempts, many times repeated,
always failed. The larva, placed in a paper boat in the centre of the
mass of honey, behaves as in the earlier experiments. Not finding what
suits it, it tries to escape and perishes in the sticky toils as soon
as it leaves the strip of paper, which it soon does.
On the other hand, we can easily rear Sitaris-grubs by taking
Anthophora-cells not invaded by the parasites, cells in which the egg
is not yet hatched. All that we have to do is to pick up one of these
grubs with the moistened tip of a needle and to lay it delicately on
the egg. There is then no longer the least attempt to escape. After
exploring the egg to find its way about, the larva rips it open and
for several days does not stir from the spot. Henceforth its
development takes place unhindered, provided that the cell be
protected from too rapid evaporation, which would dry up the honey and
render it unfit for the grub's food. The Anthophora's egg therefore is
absolutely necessary to the Sitaris-larva, not merely as a boat, but
also as its first nourishment. This is the whole secret, for lack of
knowing which I had hitherto failed in my attempts to rear the larvae
hatched in my glass jars.
At the end of a week, the egg, drained by the parasite, is nothing but
a dry skin. The first meal is finished. The Sitaris-larva, whose
dimensions have almost doubled, now splits open along the back; and
through a slit which comprises the head and the three thoracic
segments a white corpusculum, the second form of this singular
organism, escapes to fall on the surface of the honey, while the
abandoned slough remains clinging to the raft which has hitherto
safeguarded and fed the larva. Presently both sloughs, those of the
Sitaris and the egg, will disappear, submerged under the waves of
honey which the new larva is about to raise. Here ends the history of
the first form adopted by the Sitaris.
In summing up the above, we see that the strange little creature
awaits, without food, for seven months, the appearance of the
Anthophorae and at last fastens on to the hairs on the corselet of the
males, who are the first to emerge and who inevitably pass within its
reach in going through their corridors. From the fleece of the male
the larva moves, three or four weeks later, to that of the female, at
the moment of coupling; and then from the female to the egg leaving
the oviduct. It is by this concatenation of complex manoeuvres that
the larva in the end finds itself perched upon an egg in the middle of
a closed cell filled with honey. These perilous gymnastics on the hair
of a Bee in movement all the day, this passing from one sex to the
other, this arrival in the middle of the cell by way of the egg, a
dangerous bridge thrown across the sticky abyss, all this necessitates
the balancing-appliances with which it is provided and which I have
described above. Lastly, the destruction of the egg calls, in its
turn, for a sharp pair of scissors; and such is the object of the
keen, curved mandibles. Thus the primary form of the Sitares has as
its function to get itself carried by the Anthophora into the cell and
to rip up her egg. This done, the organism becomes transformed to such
a degree that repeated observations are required to make us believe
the evidence of our eyes.