THE SITARES
The high banks of sandy clay in the country round about Carpentras are
the favourite haunts of a host of Bees and Wasps, those lovers of a
thoroughly sunny aspect and of soils that are easy to excavate. Here,
in the month of May, two Anthophorae[1] are especially abundant,
gatherers of honey and, both of them, makers of subterranean cells.
One, _A. parietina_, builds at the entrance of her dwelling an
advanced fortification, an earthy cylinder, wrought in open work, like
that of the Odynerus,[2] and curved like it, but of the width and
length of a man's finger. When the community is a populous one, we
stand amazed at the rustic ornamentation formed by all these
stalactites of clay hanging from the facade. The other, _A. pilipes_,
who is very much more frequent, leaves the opening of her corridor
bare. The chinks between the stones in old walls and abandoned hovels,
the surfaces of excavations in soft sandstone or marl, are found
suitable for her labours; but the favourite spots, those to which the
greatest number of swarms resort, are vertical stretches, exposed to
the south, such as are afforded by the cuttings of deeply sunken
roads. Here, over areas many yards in width, the wall is drilled with
a multitude of holes, which impart to the earthy mass the look of some
enormous sponge. These round holes might be fashioned with an auger,
so regular are they. Each is the entrance to a winding corridor, which
runs to a depth of four to six inches. The cells are distributed at
the far end. If we would witness the labours of the industrious Bee,
we must repair to her workshop during the latter half of May. Then,
but at a respectful distance, if, as novices, we are afraid of being
stung, we may contemplate, in all its bewildering activity, the
tumultuous, buzzing swarm, busied with the building and the
provisioning of the cells.
[Footnote 1: Cf. _The Mason-bees_, by J. Henri Fabre, translated by
Alexander Teixeira de Mattos: chap. viii.; and _Bramble-bees and
Others_, by J. Henri Fabre, translated by Alexander Teixeira de
Mattos: _passim_.--_Translator's Note_.]
[Footnote 2: Cf. _The Mason-wasps_, by J. Henri Fabre, translated by
Alexander Teixeira de Mattos: chaps. vi. and x.--_Translator's Note_.]
It is most often during the months of August and September, those
happy months of the summer holidays, that I have visited the banks
inhabited by the Anthophora. At this period all is silent near the
nests; the work has long been completed; and numbers of Spiders' webs
line the crevices or plunge their silken tubes into the Bee's
corridors. Let us not, however, hastily abandon the city once so
populous, so full of life and bustle and now deserted. A few inches
below the surface, thousands of larvae and nymphs, imprisoned in their
cells of clay, are resting until the coming spring. Might not such a
succulent prey as these larvae, paralysed and incapable of defence,
tempt certain parasites who are industrious enough to attain them?
Here indeed are some Flies clad in a dismal livery, half-black,
half-white, a species of Anthrax (_A. sinuata_),[3] flying indolently
from gallery to gallery, doubtless with the object of laying their
eggs there; and here are others, more numerous, whose mission is
fulfilled and who, having died in harness, are hanging dry and
shrivelled in the Spiders' webs. Elsewhere the entire surface of a
perpendicular bank is hung with the dried corpses of a Beetle
(_Sitaris humeralis_), slung, like the Flies, in the silken meshes of
the Spiders. Among these corpses some male Sitares circle, busy,
amorous, heedless of death, mating with the first female that passes
within reach, while the fertilized females thrust their bulky abdomens
into the opening of a gallery and disappear into it backwards. It is
impossible to mistake the situation: some grave interest attracts to
this spot these two insects, which, within a few days, make their
appearance, mate, lay their eggs and die at the very doors of the
Anthophora's dwellings.
[Footnote 3: Cf. _The Life of the Fly_, by J. Henri Fabre, translated
by Alexander Teixeira de Mattos: chaps. ii. and iv.--_Translator's
Note_.]
Let us now give a few blows of the pick to the surface beneath which
the singular incidents already in our mind must be occurring, beneath
which similar things occurred last year; perhaps we shall find some
evidence of the parasitism which we suspected. If we search the
dwellings of the Anthophorae during the early days of August, this is
what we see: the cells forming the superficial layer are not like
those situated at a greater depth. This difference arises from the
fact that the same establishment is exploited simultaneously by the
Anthophora and by an Osmia (_O. tricornis_)[4] as is proved by an
observation made at the working-period, in May. The Anthophorae are
the actual pioneers, the work of boring the galleries is wholly
theirs; and their cells are situated right at the end. The Osmia
profits by the galleries which have been abandoned either because of
their age, or because of the completion of the cells occupying the
most distant part; she builds her cells by dividing these corridors
into unequal and inartistic chambers by means of rude earthen
partitions. The Osmia's sole achievement in the way of masonry is
confined to these partitions. This, by the way, is the ordinary
building-method adopted by the various Osmiae, who content themselves
with a chink between two stones, an empty Snail-shell, or the dry and
hollow stem of some plant, wherein to build their stacks of cells, at
small expense, by means of light partitions of mortar.
[Footnote 4: Cf. _Bramble-bees and Others_: _passim_.--_Translator's
Note_.]
The cells of the Anthophora, with their faultless geometrical
regularity and their perfect finish, are works of art, excavated, at a
suitable depth, in the very substance of the loamy bank, without any
manufactured part save the thick lid that closes the orifice. Thus
protected by the prudent industry of their mother, well out of reach
in their distant, solid retreats, the Anthophora's larvae are devoid
of the glandular apparatus designed for secreting silk. They therefore
never spin a cocoon, but lie naked in their cells, whose inner surface
has the polish of stucco.
In the Osmia's cells, on the other hand, means of defence are
required, for these are situated in the surface layer of the bank;
they are irregular in form, rough inside and barely protected, by
their thin earthen partitions, against external enemies. The Osmia's
larvae, in fact, contrive to enclose themselves in an egg-shaped
cocoon, dark brown in colour and very strong, which preserves them
both from the rough contact of their shapeless cells and from the
mandibles of voracious parasites, Acari,[5] Cleri[6] and Anthreni,[7]
those manifold enemies whom we find prowling in the galleries, seeking
whom they may devour. It is by means of this equipoise between the
mother's talents and the larva's that the Osmia and the Anthophora, in
their early youth, escape some part of the dangers which threaten
them. It is easy therefore, in the bank excavated by these two Bees,
to recognize the property of either species by the situation and form
of the cells and also by their contents, which consist, with the
Anthophora, of a naked larva and, with the Osmia, of a larva enclosed
in a cocoon.
[Footnote 5: Mites and Ticks.--_Translator's Note_.]
[Footnote 6: A genus of Beetles of which certain species (_Clerus
apiarius_ and _C. alvearius_) pass their preparatory state in the
nests of Bees, where they feed on the grubs.--_Translator's Note_.]
[Footnote 7: Another genus of Beetles. The grub of _A. musaeorum_, the
Museum Beetle, is very destructive to
insect-collections.--_Translator's Note_.]
On opening a certain number of these cocoons, we end by discovering
some which, in place of the Osmia's larva, contain each a curiously
shaped nymph. These nymphs, at the least shock received by their
dwelling, indulge in extravagant movements, lashing the walls with
their abdomen till the whole house shakes and dances. And, even if we
leave the cocoon intact, we are informed of their presence by a dull
rustle heard inside the silken dwelling the moment after we move it.
The fore-part of this nymph is fashioned like a sort of boar's-snout
armed with six strong spikes, a multiple ploughshare, eminently
adapted for burrowing in the soil. A double row of hooks surmounts the
dorsal ring of the four front segments of the abdomen. These are so
many grappling-irons, with whose assistance the creature is enabled to
progress in the narrow gallery dug by the snout. Lastly, a sheaf of
sharp points forms the armour of the hinder-part. If we examine
attentively the surface of the vertical wall which contains the
various nests, it will not be long before we discover nymphs like
those which we have been describing, with one extremity held in a
gallery of their own diameter, while the fore-part projects freely
into the air. But these nymphs are reduced to their cast skins, along
the back and head of which runs a long slit through which the perfect
insect has escaped. The purpose of the nymph's powerful weapons is
thus made manifest: it is the nymph that has to rend the tough cocoon
which imprisons it, to excavate the tightly-packed soil in which it is
buried, to dig a gallery with its six-pointed snout and thus to bring
to the light the perfect insect, which apparently is incapable of
performing these strenuous tasks for itself.
And in fact these nymphs, taken in their cocoons, have in a few days'
time given me a feeble Fly (_Anthrax sinuata_) who is quite incapable
of piercing the cocoon and still more of making her exit through a
soil which I cannot easily break up with my pick. Although similar
facts abound in insect history, we always notice them with a lively
interest. They tell us of an incomprehensible power which suddenly, at
a given moment, irresistibly commands an obscure grub to abandon the
retreat in which it enjoys security, in order to make its way through
a thousand difficulties and to reach the light, which would be fatal
to it on any other occasion, but which is necessary to the perfect
insect, which could not reach it by its own efforts.
But the layer of Osmia-cells has been removed; and the pick now
reaches the Anthophora's cells. Among these cells are some which
contain larvae and which result from the labours of last May; others,
though of the same date, are already occupied by the perfect insect.
The precocity of metamorphosis varies from one larva to another;
however, a few days' difference of age is enough to explain these
inequalities of development. Other cells, as numerous as the first,
contain a parasitical Hymenopteron, a Melecta (_M. armata_), likewise
in the perfect state. Lastly, there are some, indeed many, which
contain a singular egg-shaped shell, divided into segments with
projecting breathing-pores. This shell is extremely thin and fragile;
it is amber-coloured and so transparent that one can distinguish quite
plainly, through its sides, an adult Sitaris (_S. humeralis_), who
occupies the interior and is struggling as though to set herself at
liberty. This explains the presence here, the pairing and the
egg-laying of the Sitares whom we but now saw roaming, in the company
of the Anthrax-flies, at the entrance to the galleries of the
Anthophorae. The Osmia and the Anthophora, the joint owners of the
premises, have each their parasite: the Anthrax attacks the Osmia and
the Sitaris the Anthophora.
But what is this curious shell in which the Sitaris is invariably
enclosed, a shell unexampled in the Beetle order? Can this be a case
of parasitism in the second degree, that is, can the Sitaris be living
inside the chrysalis of a first parasite, which itself exists at the
cost of the Anthophora's larva or of its provisions? And, even so, how
can this parasite, or these parasites, obtain access to a cell which
seems to be inviolable, because of the depth at which it lies, and
which, moreover, does not reveal, to the most careful examination
under the magnifying-glass, any violent inroad on the enemy's part?
These are the questions that presented themselves to my mind when for
the first time, in 1855, I observed the facts which I have just
related. Three years of assiduous observation enabled me to add one of
its most astonishing chapters to the story of the formation of
insects.
After collecting a fairly large number of these enigmatical shells
containing adult Sitares, I had the satisfaction of observing, at
leisure, the emergence of the perfect insect from the shell, the act
of pairing and the laying of the eggs. The shell is easily broken; a
few strokes of the mandibles, distributed at random, a few kicks are
enough to deliver the perfect insect from its fragile prison.
In the glass jars in which I kept my Sitares I saw the pairing follow
very closely upon the first moments of freedom. I even witnessed a
fact which shows emphatically how imperious, in the perfect insect, is
the need to perform, without delay, the act intended to ensure the
preservation of its race. A female, with her head already cut out of
the shell, is anxiously struggling to release herself entirely; a
male, who has been free for a couple of hours, climbs on the shell
and, tugging here and there, with his mandibles, at the fragile
envelope, strives to deliver the female from her shackles. His efforts
are soon crowned with success; and, though the female is still three
parts swathed in her swaddling-bands, the coupling takes place
immediately, lasting about a minute. During the act, the male remains
motionless on the top of the shell, or on the top of the female when
the latter is entirely free. I do not know whether, in ordinary
circumstances, the male occasionally thus helps the female to gain her
liberty; to do so he would have to penetrate into a cell containing a
female, which, after all, is not beyond his powers, seeing that he has
been able to escape from his own. Still, on the actual site of the
cells, the coupling is generally performed at the entrance to the
galleries of the Anthophorae; and then neither of the sexes drags
about with it the least shred of the shell from which it has emerged.
After mating, the two Sitares proceed to clean their legs and antennae
by drawing them between their mandibles; then each goes his own way.
The male cowers in a crevice of the earthen bank, lingers for two or
three days and perishes. The female also, after getting rid of her
eggs, which she does without delay, dies at the entrance to the
corridor in which the eggs are laid. This is the origin of all those
corpses swinging in the Spiders' web with which the neighbourhood of
the Anthophora's dwellings is upholstered.
Thus the Sitares in the perfect state live long enough only to mate
and to lay their eggs. I have never seen one save upon the scene of
their loves, which is also that of their death; I have never surprised
one browsing on the plants near at hand, so that, though they are
provided with a normal digestive apparatus, I have grave reasons to
doubt whether they actually take any nourishment whatever. What a life
is theirs! A fortnight's feasting in a storehouse of honey; a year of
slumber underground; a minute of love in the sunlight; then death!
Once fertilized, restlessly the female at once proceeds to seek a
favourable spot wherein to lay her eggs. It was important to note
where this exact spot is. Does the female go from cell to cell,
confiding an egg to the succulent flanks of each larva, whether this
larva belong to the Anthophora or to a parasite of hers, as the
mysterious shell whence the Sitaris emerges would incline one to
believe? This method of laying the eggs, one at a time in each cell,
would appear to be essential, if we are to explain the facts already
ascertained. But then why do the cells usurped by the Sitares retain
not the slightest trace of the forcible entry which is indispensable?
And how is it that, in spite of lengthy investigations during which my
perseverance has been kept up by the keenest desire to cast some light
upon all these mysteries, how is it, I say, that I have never come
across a single specimen of the supposed parasites to which the shell
might be attributed, since this shell appears not to be a Beetle's?
The reader would hardly suspect how my slight acquaintance with
entomology was unsettled by this inextricable maze of contradictory
facts. But patience! We may yet obtain some light.
Let us begin by observing precisely at what spot the eggs are laid. A
female has just been fertilized before my eyes; she is forthwith
placed in a large glass jar, into which I put, at the same time, some
clods of earth containing Anthophora-cells. These cells are occupied
partly by larvae and partly by nymphs that are still quite white; some
are slightly open and afford a glimpse of their contents. Lastly, in
the inner surface of the cork which closes the jar I sink a
cylindrical well, a blind alley, of the same diameter as the corridors
of the Anthophora. In order that the insect, if it so desire, may
enter this artificial corridor, I lay the bottle horizontally.
The female, painfully dragging her big abdomen, perambulates all the
nooks and corners of her makeshift dwelling, exploring them with her
palpi, which she passes everywhere. After half an hour of groping and
careful investigation, she ends by selecting the horizontal gallery
dug in the cork. She thrusts her abdomen into this cavity and, with
her head hanging outside, begins her laying. Not until thirty-six
hours later was the operation completed; and during this incredible
lapse of time the patient creature remained absolutely motionless.
The eggs are white, oval and very small. They measure barely
two-thirds of a millimetre[8] in length. They stick together slightly
and are piled in a shapeless heap which might be likened to a
good-sized pinch of the unripe seeds of some orchid. As for their
number, I will admit that it tried my patience to no purpose. I do
not, however, believe that I am exaggerating when I estimate it as at
least two thousand. Here are the data on which I base this figure: the
laying, as I have said, lasts thirty-six hours; and my frequent visits
to the female working in the cavity in the cork convinced me that
there was no perceptible interruption in the successive emission of
the eggs. Now less than a minute elapses between the arrival of one
egg and that of the next; and the number of these eggs cannot
therefore be lower than the number of minutes contained in thirty-six
hours, or 2160. But the exact number is of no importance: we need only
note that it is very large, which implies, for the young larvae
issuing from the eggs, very numerous chances of destruction, since so
lavish a supply of germs is necessary to maintain the species in the
requisite proportions.
[Footnote 8: .026 inch.--_Translator's Note_.]
Enlightened by these observations and informed of the shape, the
number and the arrangement of the eggs, I searched the galleries of
the Anthophorae for those which the Sitares had laid there and
invariably found them gathered in a heap inside the galleries, at a
distance of an inch or two from the orifice, which is always open to
the outer world. Thus, contrary to what one was to some extent
entitled to suppose, the eggs are not laid in the cells of the pioneer
Bee; they are simply dumped in a heap inside the entrance to her
dwelling. Nay more, the mother does not make any protective structure
for them; she takes no pains to shield them from the rigours of
winter; she does not even attempt, by stopping for a short distance,
as best she can, the entrance-lobby in which she has laid them, to
protect them from the thousand enemies that threaten them; for, as
long as the frosts of winter have not arrived, these open galleries
are trodden by Spiders, by Acari, by Anthrenus-grubs and other
plunderers, to whom these eggs, or the young larvae about to emerge
from them, must be a dainty feast. In consequence of the mother's
heedlessness, the number of those who escape all these voracious
hunters and the inclemencies of the weather must be curiously small.
This perhaps explains why she is compelled to make up by her fecundity
for her deficient industry.
The hatching occurs a month later, about the end of September or the
beginning of October. The season being still propitious, I was led to
suppose that the young larvae must at once make a start and disperse,
in order that each might seek to gain access, through some
imperceptible fissure, to an Anthophora-cell. This presumption turned
out to be entirely at fault. In the boxes in which I had placed the
eggs laid by my captives, the young larvae, little black creatures at
most a twenty-fifth of an inch long, did not move away, provided
though they were with vigorous legs; they remained higgledy-piggledy
with the white skins of the eggs whence they had emerged.
In vain I placed within their reach lumps of earth containing nests of
the Anthophora, open cells, larvae and nymphs of the Bee: nothing was
able to tempt them; they persisted in forming, with the egg-skins, a
powdery heap of speckled black and white. It was only by drawing the
point of a needle through this pinch of living dust that I was able to
provoke an active wriggling. Apart from this, all was still. If I
forcibly removed a few larvae from the common heap, they at once
hurried back to it, in order to hide themselves among the rest.
Perhaps they had less reason to fear the cold when thus collected and
sheltered beneath the egg-skins. Whatever may be the motive that
impels them to remain thus gathered in a heap, I recognized that none
of the means suggested by my imagination succeeded in forcing them to
abandon the little spongy mass formed by the skins of the eggs, which
were slightly glued together. Lastly, to assure myself that the
larvae, in the free state, do not disperse after they are hatched, I
went during the winter to Carpentras and inspected the banks inhabited
by the Anthophorae. There, as in my boxes, I found the larvae piled
into heaps, all mixed up with the skins of the eggs.