While working on a sermon the pastor heard a knock at his office door. "Come in," he invited. A sad-looking man in threadbare clothes came in, pulling a large pig on a rope. "Can I talk to you for a minute?" asked the ma... Read more of Kids On Marriage at Free Jokes.caInformational Site Network Informational
Privacy
   Home - Articles - Books

THE BUMBLEBEE FLY




Underneath the wasp's brown paper manor house, the ground is
channeled into a sort of drain for the refuse of the nest. Here
are shot the dead or weakly larvae which a continual inspection
roots out from the cells to make room for fresh occupants; here, at
the time of the autumn massacre, are flung the backward grubs;
here, lastly, lies a good part of the crowd killed by the first
touch of winter. During the rack and ruin of November and
December, this sewer becomes crammed with animal matter.

Such riches will not remain unemployed. The world's great law
which says that nothing edible shall be wasted provides for the
consumption of a mere ball of hair disgorged by the owl. How shall
it be with the vast stores of a ruined wasps' nest! If they have
not come yet, the consumers whose task it is to salve this abundant
wreckage for nature's markets, they will not tarry in coming and
waiting for the manna that will soon descend from above. That
public granary, lavishly stocked by death, will become a busy
factory of fresh life. Who are the guests summoned to the banquet?

If the wasps flew away, carrying the dead or sickly grubs with
them, and dropped them on the ground round about their home, those
banqueters would be, first and foremost, the insect-eating birds,
the warblers, all of whom are lovers of small game. In this
connection, we will allow ourselves a brief digression. We all
know with what jealous intolerance the nightingales occupy each his
own cantonment. Neighborly intercourse among them is tabooed. The
males frequently exchange defiant couplets at a distance; but,
should the challenged party draw near, the challenger makes him
clear off. Now, not far from my house, in a scanty clump of holly
oaks which would barely give the woodcutter the wherewithal for a
dozen faggots, I used, all through the spring, to hear such full-
throated warbling of nightingales that the songs of those virtuosi,
all giving voice at once and with no attempt at order, degenerated
into a deafening hubbub.

Why did those passionate devotees of solitude come and settle in
such large numbers at a spot where custom decrees that there is
just room enough for one household only? What reasons have made
the recluse become a congregation? I asked the owner of the
spinney about the matter.

'It's like that every year,' he said. 'The clump is overrun by
Nightingales.'

'And the reason? '

'The reason is that there is a hive close by, behind that wall.'

I looked at the man in amazement, unable to understand what
connection there could be between a hive and the thronging
nightingales.

'Why, yes,' he added, 'there are a lot of nightingales because
there are a lot of bees.

Another questioning look from my side. I did not yet understand.
The explanation came: 'The bees,' he said, 'throw out their dead
grubs. The front of the hive is strewn with them in the mornings;
and the nightingales come and collect them for themselves and their
families. They are very fond of them.'

This time I had solved the puzzle. Delicious food, abundant and
fresh each day, had brought the songsters together. Contrary to
their habit, numbers of nightingales are living on friendly terms
in a cluster of bushes, in order to be near the hive and to have a
larger share in the morning distribution of plump dainties.

In the same way, the nightingale and his gastronomical rivals would
haunt the neighborhood of the wasps' nests, if the dead grubs were
cast out on the surface of the soil; but these delicacies fall
inside the burrow and no little bird would dare to enter the murky
cave, even if the entrance were not too small to admit it. Other
consumers are needed here, small in size and great in daring; the
fly is called for and her maggot, the king of the departed. What
the greenbottles, the bluebottles and the flesh flies do in the
open air, at the expense of every kind of corpse, other flies,
narrowing their province, do underground at the Wasps' expense.

Let us turn our attention, in September, to the wrapper of a wasps'
nest. On the outer surface and there alone, this wrapper is strewn
with a multitude of big, white, elliptical dots, firmly fixed to
the brown paper and measuring about two millimeters and a half long
by one and a half wide. Flat below, convex above and of a lustrous
white, these dots resemble very neat drops fallen from a tallow
candle. Lastly, their backs are streaked with faint transversal
lines, an elegant detail perceptible only with the lens. These
curious objects are scattered all over the surface of the wrapper,
sometimes at a distance from one another, sometimes gathered into
more or less dense groups. They are the eggs of the Volucella, or
bumblebee fly (Volucella zonaria, LIN.)

Also stuck to the brown paper of the outer wrapper and mixed up
with the Volucella's are a large number of other eggs, chalk white,
spear-shaped and ridged lengthwise with seven or eight thin ribs,
after the manner of the seeds of certain Umbelliferae. The
finishing touch to their delicate beauty is the fine stippling all
over the surface. They are smaller by half than the others. I
have seen grubs come out of them which might easily be the earliest
stage of some pointed maggots which I have already noticed in the
burrows. My attempts to rear them failed; and I am not able to say
which fly these eggs belong to. Enough for us to note the nameless
one in passing. There are plenty of others, which we must make up
our minds to leave unlabelled, in view of the jumbled crowd of
feasters in the ruined wasps' nest. We will concern ourselves only
with the most remarkable, in the front rank of which stands the
bumblebee Fly.

She is a gorgeous and powerful fly; and her costume, with its brown
and yellow bands, shows a vague resemblance to that of the wasps.
Our fashionable theorists have availed themselves of this brown and
yellow to cite the Volucella as a striking instance of protective
mimicry. Obliged, if not on her own behalf, at least on that of
her family, to introduce herself as a parasite into the wasp's
home, she resorts, they tell us, to trickery and craftily dons her
victim's livery. Once inside the wasps' nest, she is taken for one
of the inhabitants and attends quietly to her business.

The simplicity of the wasp, duped by a very clumsy imitation of her
garb, and the depravity of the fly, concealing her identity under a
counterfeit presentment, exceed the limits of my credulity. The
wasp is not so silly nor the Volucella so clever as we are assured.
If the latter really meant to deceive the Wasp by her appearance,
we must admit that her disguise is none too successful. Yellow
sashes round the abdomen do not make a wasp. It would need more
than that and, above all, a slender figure and a nimble carriage;
and the Volucella is thickset and corpulent and sedate in her
movements. Never will the wasp take that unwieldy insect for one
of her own kind. The difference is too great.

Poor Volucella, mimesis has not taught you enough. You ought--this
is the essential point--to have adopted a wasp's shape; and that
you forgot to do: you remained a fat fly, easily recognizable.
Nevertheless, you penetrate into the terrible cavern; you are able
to stay there for a long time, without danger, as the eggs
profusely strewn on the wrapper of the wasps' nest show. How do
you set about it?

Let us, first of all, remember that the bumblebee fly does not
enter the enclosure in which the combs are heaped: she keeps to the
outer surface of the paper rampart and there lays her eggs. Let
us, on the other hand, recall the Polistes [a tree nesting wasp]
placed in the company of the wasps in my vivarium. Here of a
surety is one who need not have recourse to mimicry to find
acceptance. She belongs to the guild, she is a wasp herself. Any
of us that had not the trained eye of the entomologist would
confuse the two species. Well, this stranger, as long as she does
not become too importunate, is quite readily tolerated by the caged
wasps. None seeks to pick a quarrel with her. She is even
admitted to the table, the strip of paper smeared with honey. But
she is doomed if she inadvertently sets foot upon the combs. Her
costume, her shape, her size, which tally almost exactly with the
costume, shape and size of the wasp, do not save her from her fate.
She is at once recognized as a stranger and attacked and
slaughtered with the same vigor as the larvae of the Hylotoma
sawfly and the Saperda beetle, neither of which bears any outward
resemblance to the larva of the wasps.

Seeing that identity of shape and costume does not save the
Polistes, how will the Volucella fare, with her clumsy imitation?
The wasp's eye, which is able to discern the dissimilar in the
like, will refuse to be caught. The moment she is recognized, the
stranger is killed on the spot. As to that there is not the shadow
of a doubt.

In the absence of bumblebee flies at the moment of experimenting, I
employ another fly, Milesia fulminans, who, thanks to her slim
figure and her handsome yellow bands, presents a much more striking
likeness to the wasp than does the fat Volucella zonaria. Despite
this resemblance, if she rashly venture on the combs, she is
stabbed and slain. Her yellow sashes, her slender abdomen deceive
nobody. The stranger is recognized behind the features of a
double.

My experiments under glass, which varied according to the captures
which I happened to make, all lead me to this conclusion: as long
as there is more propinquity, even around the honey, the other
occupants are tolerated fairly well; but, if they touch the cells,
they are assaulted and often killed, without distinction of shape
or costume. The grubs' dormitory is the sanctum sanctorum which no
outsider must enter under pain of death.

With these caged captives I experiment by daylight, whereas the
free wasps work in the absolute darkness of their underground
retreat. Where light is absent, color goes for nothing. Once,
therefore, that she has entered the cavern, the bumblebee fly
derives no benefit from her yellow bands, which are supposed to be
her safeguard. Whether garbed as she is or otherwise, it is easy
for her to effect her purpose in the dark, on condition that she
avoids the tumultuous interior of the wasps' nest. So long as she
has the prudence not to hustle the passers by, she can dab her
eggs, without danger, on the paper wall. No one will know of her
presence. The dangerous thing is to cross the threshold of the
burrow in broad daylight, before the eyes of those who go in and
out. At that moment alone, protective mimicry would be convenient.
Now does the entrance of the Volucella into the presence of a few
wasps entail such very great risks? The wasps' nest in my
enclosure, the one which was afterwards to perish in the sun under
a bell glass, gave me the opportunity for prolonged observations,
but without any result upon the subject of my immediate concern.
The bumblebee fly did not appear. The period for her visits had
doubtless passed; for I found plenty of her grubs when the nest was
dug up.

Other flies rewarded me for my assiduity. I saw some--at a
respectful distance, I need hardly say--entering the burrow. They
were insignificant in size and of a dark gray color, not unlike
that of the housefly. They had not a patch of yellow about them
and certainly had no claim to protective mimicry. Nevertheless,
they went in and out as they pleased, calmly, as though they were
at home. As long as there was not too great a number at the door,
the wasps left them alone. When there was anything of a crowd, the
gray visitors waited near the threshold for a less busy moment. No
harm came to them.

Inside the establishment, the same peaceful relations prevail. In
this respect I have the evidence of my excavations. In the
underground charnel house, so rich in Fly grubs, I find no corpses
of adult flies. If the strangers had been slaughtered in passing
through the entrance hall, or lower down, they would fall to the
bottom of the burrow anyhow, with the other rubbish. Now in this
charnel house, as I said, there are never any dead bumblebee flies,
never a fly of any sort. The incomers are respected. Having done
their business, they go out unscathed.

This tolerance on the part of the wasps is surprising. And a
suspicion comes to one's mind: can it be that the Volucella and the
rest are not what the accepted theories of natural history call
them, namely, enemies, grub killers sacking the wasps' nest? We
will look into this by examining them when they are hatched.
Nothing is easier, in September and October, than to collect the
Volucella's eggs in such numbers as we please. They abound on the
outer surface of the wasps' nest. Moreover, as with the larvae of
the wasp, it is some time before they are suffocated by the
petroleum fumes; and so most of them are sure to hatch. I take my
scissors, cut the most densely populated bits from the paper wall
of the nest and fill a jar with them. This is the warehouse from
which I shall daily, for the best part of the next two months, draw
my supply of nascent grubs.

The Volucella's egg remains where it is, with its white color
always strongly marked against the brown of the background. The
shell wrinkles and collapses; and the fore end tears open. From it
there issues a pretty little white grub, thin in front, swelling
slightly in the rear and bristling all over with fleshy
protuberances. The creature's papillae are set on its sides like
the teeth of a comb; at the rear, they lengthen and spread into a
fan; on the back, they are shorter and arranged in four
longitudinal rows. The last section but one carries two short,
bright red breathing tubes, standing aslant and joined to each
other. The fore part, near the pointed mouth, is of a darker,
brownish color. This is the biting and motor apparatus, seen
through the skin and consisting of two fangs. Taken all round, the
grub is a pretty little thing, with its bristling whiteness, which
gives it the appearance of a tiny snowflake. But this elegance
does not last long: grown big and strong, the bumblebee fly's grub
becomes soiled with sanies, turns a russety brown and crawls about
in the guise of a hulking porcupine.

What becomes of it when it leaves the egg? This my warehousing jar
tells me, partly. Unable to keep its balance on sloping surfaces,
it drops to the bottom of the receptacle, where I find it, daily,
as hatched, wandering restlessly. Things must happen likewise at
the wasps'. Incapable of standing on the slant of the paper wall,
the newborn grubs slide to the bottom of the underground cavity,
which contains, especially at the end of the summer, a heaped up
provender of deceased wasps and dead larvae removed from the cells
and flung outside the house, all nice and gamy, as proper maggot's
food should be.
The Volucella's offspring, themselves maggots, notwithstanding
their snowy apparel, find in this charnel house victuals to their
liking, incessantly renewed. Their fall from the high walls might
well be not accidental, but rather a means of reaching, quickly and
without searching, the good things down at the bottom of the
cavern. Perhaps, also, some of the white grubs, thanks to the
holes that make the wrapper resemble a spongy cover, manage to slip
inside the Wasps' nest. Still, most of the Volucella's grubs, at
whatever stage of their development, are in the basement of the
burrow, among the carrion remains. The others, those settled in
the wasps' home itself, are comparatively few.

These returns are enough to show us that the grubs of the bumblebee
fly do not deserve the bad reputation that has been given them.
Satisfied with the spoils of the dead, they do not touch the
living; they do not ravage the wasps' nest: they disinfect it.

Experiment confirms what we have learnt in the actual nests. Over
and over again, I bring wasp grubs and Volucella grubs together in
small test tubes, which are easy to observe. The first are well
and strong; I have just taken them from their cells. The others
are in various stages, from that of the snowflake born the same day
to that of the sturdy porcupine. There is nothing tragic about the
encounter. The grubs of the bumblebee fly roam about the test-tube
without touching the live tidbit. The most that they do is to put
their mouths for a moment to the morsel; then they take it away
again, not caring for the dish.

They want something different: a wounded, a dying grub; a corpse
dissolving into sanies. Indeed, if I prick the wasp grub with a
needle, the scornful ones at once come and sup at the bleeding
wound. If I give them a dead grub, brown with putrefaction, the
worms rip it open and feast on its humors. Better still: I can
feed them quite satisfactorily with wasps that have turned putrid
under their horny rings; I see them greedily suck the juices of
decomposing Rosechafer grubs; I can keep them thriving with chopped
up butcher's meat, which they know how to liquefy by the method of
the common maggot. And these unprejudiced ones, who accept
anything that comes their way, provided it be dead, refuse it when
it is alive. Like the true flies that they are, frank body
snatchers, they wait, before touching a morsel, for death to do its
work.

Inside the wasps' nest, robust grubs are the rule and weaklings the
rare exception, because of the assiduous supervision which
eliminates anything that is diseased and like to die. Here,
nevertheless, Volucella grubs are found, on the combs, among the
busy wasps. They are not, it is true, so numerous as in the
charnel house below, but still pretty frequent. Now what do they
do in this abode where there are no corpses? Do they attack the
healthy? Their continual visits from cell to cell would at first
make one think so; but we shall soon be undeceived if we observe
their movements closely; and this is possible with my glass roofed
colonies.

I see them fussily crawling on the surface of the combs, curving
their necks from side to side and taking stock of the cells. This
one does not suit, nor that one either; the bristly creature passes
on, still in search, thrusting its pointed fore part now here, now
there. This time, the cell appears to fulfil the requisite
conditions. A larva, glowing with health, opens wide its mouth,
believing its nurse to be approaching. It fills the hexagonal
chamber with its bulging sides.

The gluttonous visitor bends and slides its slender fore part, a
blade of exquisite suppleness, between the wall and the inhabitant,
whose slack rotundity yields to the pressure of this animated
wedge. It plunges into the cell, leaving no part of itself outside
but its wide hind quarters, with the red dots of the two breathing
tubes.

It remains in this posture for some time, occupied with its work at
the bottom of the cell. Meanwhile, the wasps present do not
interfere, remain impassive, showing that the grub visited is in no
peril. The stranger, in fact, withdraws with a soft, gliding
motion. The chubby babe, a sort of India rubber bag, resumes its
original volume without having suffered any harm, as its appetite
proves. A nurse offers it a mouthful, which it accepts with every
sign of unimpaired vigor. As for the Volucella grub, it licks its
lips after its own fashion, pushing its two fangs in and out; then,
without further loss of time, goes and repeats its probing
elsewhere.

What it wants down there, at the bottom of the cells, behind the
grubs, cannot be decided by direct observation; it must be guessed
at. Since the visited larva remains intact, it is not prey that
the Volucella grub is after. Besides, if murder formed part of its
plans, why descend to the bottom of the cell, instead of attacking
the defenseless recluse straight way? It would be much easier to
suck the patient's juices through the actual orifice of the cell.
Instead of that, we see a dip, always a dip and never any other
tactics.

Then what is there behind the wasp grub? Let us try to put it as
decently as possible. In spite of its exceeding cleanliness, this
grub is not exempt from the physiological ills inseparable from the
stomach. Like all that eats, it has intestinal waste matter with
regard to which its confinement compels it to behave with extreme
discretion. Like so many other close-cabined larvae of Wasps and
Bees, it waits until the moment of the transformation to rid itself
of its digestive refuse. Then, once and for all, it casts out the
unclean accumulation whereof the pupa, that delicate, reborn
organism, must not retain the least trace. This is found later, in
any empty cell, in the form of a dark purple plug. But, without
waiting for this final purge, this lump, there are, from time to
time, slight excretions of fluid, clear as water. We have only to
keep a Wasp grub in a little glass tube to recognize these
occasional discharges. Well, I see nothing else to explain the
action of the Volucella's grubs when they dip into the cells
without wounding the larvae. They are looking for this liquid,
they provoke its emission. It represents to them a dainty which
they enjoy over and above the more substantial fare provided by the
corpses.

The bumblebee fly, that sanitary inspector of the Vespine city,
fulfils a double office: she wipes the wasp's children and she rids
the nest of its dead. For this reason, she is peacefully received,
as an auxiliary, when she enters the burrow to lay her eggs; for
this reason, her grub is tolerated, nay more, respected, in the
very heart of the dwelling, where none might stray with impunity.
I remember the brutal reception given to the Saperda and Hylotoma
grubs when I place them on a comb. Forthwith grabbed, bruised and
riddled with stings, the poor wretches perish. It is quite a
different matter with the offspring of the Volucella. They come
and go as they please, poke about in the cells, elbow the
inhabitants and remain unmolested. Let us give some instances of
this clemency, which is very strange in the irascible Wasp.

For a couple of hours, I fix my attention on a Volucella grub
established in a cell, side by side with the Wasp grub, the
mistress of the house. The hind quarters emerge, displaying their
papillae. Sometimes also the fore part, the head, shows, bending
from side to side with sudden, snake-like motions. The wasps have
just filled their crops at the honey pot; they are dispensing the
rations, are very busily at work; and things are taking place in
broad daylight, on the table by the window.

As they pass from cell to cell, the nurses repeatedly brush against
and stride across the Volucella grub. There is no doubt that they
see it. The intruder does not budge, or, if trodden on, curls up,
only to reappear the next moment. Some of the wasps stop, bend
their heads over the opening, seem to be making inquiries and then
go off, without troubling further about the state of things. One
of them does something even more remarkable: she tries to give a
mouthful to the lawful occupant of the cell; but the larva, which
is being squeezed by its visitor, has no appetite and refuses.
Without the least sign of anxiety on behalf of the nursling which
she sees in awkward company, the wasp retires and goes to
distribute its ration elsewhere. In vain I prolong my examination:
there is no fluster of any kind. The Volucella grub is treated as
a friend, or at least as a visitor that does not matter. There is
no attempt to dislodge it, to worry it, to put it to flight. Nor
does the grub seem to trouble greatly about those who come and go.
Its tranquillity, tells us that it feels at home.

Here is some further evidence: the grub has plunged, head
downwards, into an empty cell, which is too small to contain the
whole of it. Its hindquarters stick out, very visibly. For long
hours, it remains motionless in this position. At every moment,
wasps pass and repass close by. Three of them, at one time
together, at another separately, come and nibble at the edges of
the cell; they break off particles which they reduce to paste for a
new piece of work. The passers by, intent upon their business, may
not perceive the intruder; but these three certainly do. During
their work of demolition, they touch the grub with their legs,
their antennae, their palpi; and yet none of them minds it. The
fat grub, so easily recognized by its queer figure, is left alone;
and this in broad daylight, where everybody can see it. What must
it be when the profound darkness of the burrows protects the
visitor with its mysteries!

I have been experimenting all along with big Volucella grubs,
colored with the dirty red which comes with age. What effect will
pure white produce? I sprinkle on the surface of the combs some
larvae that have lately left the egg. The tiny, snow-white grubs
make for the nearest cells, go down into them, come out again and
hunt elsewhere. The wasps peaceably let them go their way, as
heedless of the little white invaders as of the big red ones.
Sometimes, when it enters an occupied cell, the little creature is
seized by the owner, the wasp grub, which nabs it and turns and
returns it between its mandibles. Is this a defensive bite? No,
the wasp grub has merely blundered, taking its visitor for a
proffered mouthful. There is no great harm done. Thanks to its
suppleness, the little grub emerges from the grip intact and
continues its investigations.

It might occur to us to attribute this tolerance to some lack of
penetration in the wasps' vision. What follows will undeceive us:
I place separately, in empty cells, a grub of Saperda scalaria and
a Volucella grub, both of them white and selected so as not to fill
the cell entirely. Their presence is revealed only by the paleness
of the hind part which serves as a plug to the opening. A
superficial examination would leave the nature of the recluse
undecided. The wasps make no mistake: they extirpate the Saperda
grub, kill it, fling it on the dust heap; they leave the Volucella
grub in peace.

The two strangers are quite well recognized in the secrecy of the
cells: one is the intruder that must be turned out; the other is
the regular visitor that must be respected. Sight helps, for
things take place in the daylight, under glass; but the wasps have
other means of information in the dimness of the burrow. When I
produce darkness by covering the apparatus with a screen, the
murder of the trespassers is accomplished just the same. For so
say the police regulations of the wasps' nest: any stranger
discovered must be slain and thrown on the midden.

To thwart this vigilance, the real enemies need to be masters of
the art of deceptive immobility and cunning disguise. But there is
no deception about the Volucella grub. It comes and goes, openly,
wheresoever it will; it looks round amongst the wasps for cells to
suit it. What has it to make itself thus respected? Strength?
Certainly not. It is a harmless creature, which the wasp could rip
open with a blow of her shears, while a touch of the sting would
mean lightning death. It is a familiar guest, to whom no denizen
of a wasps' nest bears any ill will. Why? Because it renders good
service: so far from working mischief, it does the scavenging for
its hosts. Were it an enemy or merely an intruder, it would be
exterminated; as a deserving assistant, it is respected.

Then what need is there for the Volucella to disguise herself as a
wasp? Any fly, whether clad in drab or motley, is admitted to the
burrow directly she makes herself useful to the community. The
mimicry of the bumblebee fly, which was said to be one of the most
conclusive cases, is, after all, a mere childish notion. Patient
observation, continually face to face with facts, will have none of
it and leaves it to the armchair naturalists, who are too prone to
look at the animal world through the illusive mists of theory,





Next: MATHEMATICAL MEMORIES: NEWTON'S BINOMIAL THEOREM

Previous: THE GREY FLESH FLIES



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