THE VOLUCELLA

The Mason-Wasps by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE VOLUCELLA

CHAPTER XII. THE VOLUCELLA

Underneath the brown-paper manor-house, let us once more say, the ground is channelled into a sort of drain for the refuse of the nest. Here are shot the dead or weakly larvæ 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.

Everybody knows with what jealous intolerance the Nightingales occupy each his own cantonment. Neighbourly 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 a wood-cutter the wherewithal to make a dozen faggots, I used, all through the spring, to hear such full-throated warbling of Nightingales that the songs of these 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 [290]at a spot where custom decrees that there is just room for one household only? What reasons have turned the recluse into 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 stand of hives close by, behind that wall.”

I looked at the man in amazement, unable to understand what connection there could be between a stand of hives 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 stand 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 [291]to their habit, numbers of Nightingales are living on friendly terms in a cluster of bushes, in order to be near the hives 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 neighbourhood 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, Bluebottles and Flesh-flies1 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, oval dots, firmly fixed to the brown paper and measuring roughly one-tenth of an inch long by one-sixteenth of an inch wide. Flat [292]below, convex above and of a lustrous white, these dots resemble very neat drops 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 Bumble-bee Fly (V. zonaria, Poda).

Also stuck to the brown paper of the outer envelope 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 Umbelliferæ. 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 to which Fly these eggs belong. 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 [293]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 Volucella.

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 [294]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 unwieldly 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 you forgot to do so; you remained a fat Fly, far too easily recognized. 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 Volucella does not enter the enclosure in which the combs are stacked: she keeps to the outer surface of the paper rampart and there lays her eggs. Let us, on the other hand, recall the Polistes placed in the company of the Wasps in my breeding-cage. 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, so long as she does not [295]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 vigour as the larvæ of the Hylotoma and the Saperda, neither of which bears any outward resemblance to the Wasps.

If identity of shape and costume do 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 Volucellæ 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 V. zonaria. Despite [296]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 wire-gauze, which vary according to the captures which I happen to make, all lead me to this conclusion: so long as there is mere propinquity, even around the honey, the other prisoners 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 crypt. Where light is absent, colour goes for nothing. Once, therefore, that she has entered the cavern, the Volucella 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 avoid 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, [297]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 under a bell-glass in the sun, gave me the opportunity for prolonged observations, but without any result upon the subject of my immediate concern. The Volucella 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-grey colour, not unlike that of the House-fly. 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. So long as there was not too great a number at the door, the Wasps left them alone. When there was anything of a [298]crowd, the grey 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 were slaughtered in passing through the entrance-hall or lower down, they would fall to the bottom of the burrow promiscuously with the other rubbish. Now in this charnel-pit, as I said, there are never any dead Volucellæ, never a Fly of any sort. The incomers, therefore, 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 [299]larvæ of the Wasp, it is some time before they are suffocated by the petrol; and the great majority 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 infant grubs.

The Volucella’s egg remains where it is, with its white colouring strongly marked against the grey background of the support; The shell wrinkles and collapses; and the fore-end tears open. From it there issues a pretty little white grub, thin in front, widening slightly in the rear and bristling all over with fleshy papillæ. These papillæ are set, on the creature’s 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 segment but one carries two short, bright-red breathing-tubes, standing aslant and joined to each other. The forepart, near the pointed mouth, is of a darker, brownish colour. This is the biting- and motor-apparatus, seen through the skin and consisting of two fang’s. Taken all round, the grub is a comely little thing, with its [300]bristling whiteness, which gives it the appearance of a tiny snow-flake. But this elegance does not last long: grown big and strong, the Volucella’s grub becomes soiled with sanies, turns russet-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 and when hatched, restlessly wandering. Things must happen likewise at the Wasps’. Incapable of standing on the slant of the paper wall, the new-born grubs slide to the bottom of the underground cavity, which contains, especially at the end of the summer, a plentiful provender of deceased Wasps and dead larvæ removed from the cells and flung outside, 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, [301]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 larvæ, 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 Volucella 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 snow-flake born the same day to that of the sturdy Porcupine.

There is nothing tragic about the encounter. The Flies’ grubs roam about the test-tube without touching the live tit-bit. 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.[302]

They want something different: a wounded, a dying creature; a corpse dissolving into sanies. Indeed, if I prick the Wasp-grub with a needle, the scornful ones immediately come and sup at the bleeding wound. If I give them a dead larva, brown with putrefaction, the grubs rip it open and feast on its humours. 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 Cetonia-larvæ; 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 whatever comes their way, provided that it be dead, refuse it when it is alive. Like the true Flies and frank body-snatchers that they are, they wait, before touching a morsel, for death to do its work.

Inside the Wasps’-nest, robust larvæ are the rule and weaklings the rare exception, because of the assiduous supervision which eliminates anything that is 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 they are pretty frequent. Now what do they [303]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 caged colonies.

I see them fussily crawling on the surface of the combs, swaying 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 quest of something, 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 slips 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 remain [304]impassive, do not interfere, a clear proof that the grub visited is in no peril. The stranger, in fact, retires 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 soon shows. A nurse offers it a mouthful, which it accepts with every sign of unimpaired vigour. As for the Volucella-grub, it licks its lips for a few moments after its own fashion, pushing its two fangs in and out; then, without further loss of time, it 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’s grub is after. Besides, if murder formed part of its plans, why dive to the bottom of the cell, instead of attacking the defenceless recluse straightway? 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 word all this as decently as we can. In spite of its exceeding cleanliness, [305]the grub is not exempt from the physiological ills inseparable from the work of the stomach. Like all that eats, it has intestinal waste matter in regard to which its confinement compels it to behave with extreme discretion. Like so many other close-cabined larvæ 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 larvæ. 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 Volucella, that sanitary inspector of the Vespian city, fulfils a double office: she gives the Wasp’s children a wipe down; and [306]she rids the Wasps’-nest of its dead. For this reason, she is peacefully received, as an assistant, when she enters the burrow to lay her eggs there; 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 welcome accorded to the Saperda- and Hylotoma-larvæ when I place them upon 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 papillæ. Sometimes also the pointed fore-part, the head, appears, bending from side to side with sudden, Snake-like motions. The Wasps have just filled their crops at the honey-puddle; they are dispensing the rations, are very busily at work; and these things are taking place in broad daylight, on my table, by the window.[307]

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, retires inside, only to reappear the next moment. Some of the Wasps stop, bend their heads over the opening, seem to be making enquiries 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 nurseling which she has seen in awkward company, the Wasp retires and goes to distribute her 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 [308]of it. Its hind-quarters 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 antennæ, 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, coloured with the dirty red that comes with age. What effect will pure white produce? I sprinkle on the surface of the combs some larvæ 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 about elsewhere. The Wasps peaceably let them go their way, as heedless of the little white [309]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 it over and over in 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 litheness, the little grub escapes intact from the grip 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 larva of the Scalary Saperda and a Volucella-larva, 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, throw it into the rubbish-pit; 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 [310]is the regular visitor that must be respected. Sight helps, for things take place in the daylight, under my cage; 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 stealthy immobility and cunning dissimulation. But there is no dissimulation 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 Wasp’-nest bears ill-will. Why? Because it renders good service: so far from working mischief, it does the scavenging. Were it an enemy or merely an intruder, it would be exterminated; as a deserving assistant it is respected.[311]

Then what need is there for the Volucella to disguise herself as a Wasp? Any Fly, whether grey or motley, is admitted to the burrow directly she makes herself useful to the community. The mimicry of the Volucella, 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 arm-chair naturalists, who are too prone to look at the animal world through the illusive mists of theory.

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