Chapter VIII. Parasites
Jean-Henri Fabre Mason-bees
Chrysis Ignita Wasp
In August or September, let us go into some gorge with bare and sun-scorched sides. When we find a slope well-baked by the summer heat, a quiet corner with the temperature of an oven, we will call a halt: there is a fine harvest to be gathered there. This tropical land is the native soil of a host of Wasps and Bees, some of them busily piling the household provisions in underground warehouses: here a stack of Weevils, Locusts or Spiders, there a whole assortment of Flies, Bees, Mantes or Caterpillars, while others are storing up honey in membranous wallets or clay pots, or else in cottony bags or urns made with the punched-out disks of leaves.
With the industrious folk who go quietly about their business, the labourers, masons, foragers, warehousers, mingles the parasitic tribe, the prowlers hurrying from one home to the next, lying in wait at the doors, watching for a favourable opportunity to settle their family at the expense of others.
A heart-rending struggle, in truth, is that which rules the insect world and in a measure our own world too. No sooner has a worker, by dint of exhausting labour, amassed a fortune for his children than the non-producers come hastening up to contend for its possession. To one who amasses there are sometimes five, six or more bent upon his ruin; and often it ends not merely in robbery but in black murder. The worker's family, the object of so much care, for whom that home was built and those provisions stored, succumb, devoured by the intruders, directly the little bodies have acquired the soft roundness of youth. Shut up in a cell that is closed on every side, protected by its silken covering, the grub, once its victuals are consumed, sinks into a profound slumber, during which the organic changes needed for the future transformation take place. For this new hatching, which is to turn a grub into a Bee, for this general remodelling, the delicacy of which demands absolute repose, all the precautions that make for safety have been taken.
These precautions will be foiled. The enemy will succeed in penetrating the impregnable fortress; each foe has his special tactics, contrived with appalling skill. See, an egg is inserted by means of a probe beside the torpid larva; or else, in the absence of such an implement, an infinitesimal grub, an atom, comes creeping and crawling, slips in and reaches the sleeper, who will never wake again, already a succulent morsel for her ferocious visitor. The interloper makes the victim's cell and cocoon his own cell and his own cocoon; and next year, instead of the mistress of the house, there will come from below ground the bandit who usurped the dwelling and consumed the occupant.
Look at this one, striped black, white and red, with the figure of a clumsy, hairy Ant. She explores the slope on foot, inspects every nook and corner, sounds the soil with her antennae. She is a Mutilla, the scourge of the cradled grubs. The female has no wings, but, being a Wasp, she carries a sharp poniard. To novice eyes she would easily pass for a sort of robust Ant, distinguished from the common ruck by her garb of staring motley. The male, wide-winged and more gracefully shaped, hovers incessantly a few inches above the sandy expanse. For hours at a time, on the same spot, after the manner of the Scolia-wasp he spies the coming of the females out of the ground. If our watch be patient and persevering, we shall see the mother, after trotting about for a bit, stop somewhere and begin to scratch and dig, finally laying bare a subterranean gallery, of which there was nothing to betray the entrance; but she can discern what is invisible to us. She penetrates into the abode, remains there for a while and at last reappears to replace the rubbish and close the door as it was at the start. The abominable deed is done: the Mutilla's egg has been laid in another's cocoon, beside the slumbering larva on which the newborn grub will feed.
Here are others, all aglitter with metallic gleams: gold, emerald, blue and purple. They are the humming-birds of the insect-world, the Chrysis-wasps, or Golden Wasps, another set of exterminators of the larvae overcome with lethargy in their cocoons. In them, the atrocious assassin of cradled children lies hidden under the splendour of the garb. One of them, half emerald and half pale-pink, Parnopes carnea by name, boldly enters the burrow of Bembex rostrata at the very moment when the mother is at home, bringing a fresh piece to her larva, whom she feeds from day to day. To the elegant criminal, unskilled in navvy's work, this is the one moment to find the door open. If the mother were away, the house would be shut up; and the Golden Wasp, that sneak-thief in royal robes, could not get in. She enters, therefore, dwarf as she is, the house of the giantess whose ruin she is meditating; she makes her way right to the back, all heedless of the Bembex, her sting and her powerful jaws. What cares she that the home is not deserted? Either unmindful of the danger or paralysed with terror, the Bembex mother lets her have her way.
The unconcern of the invaded is equalled only by the boldness of the invader. Have I not seen the Anthophora-bee, at the door to her dwelling, stand a little to one side and make room for the Melecta to enter the honey-stocked cells and substitute her family for the unhappy parent's? One would think that they were two friends meeting on the threshold, one going in, the other out!
It is written in the book of fate: everything shall happen without impediment in the burrow of the Bembex; and next year, if we open the cells of that mighty huntress of Gad-flies, we shall find some which contain a russet-silk cocoon, the shape of a thimble with its orifice closed with a flat lid. In this silky tabernacle, which is protected by the hard outer shell, is a Parnopes carnea. As for the grub of the Bembex, that grub which wove the silk and next encrusted the outer casing with sand, it has disappeared entirely, all but the tattered remnants of its skin. Disappeared how? The Golden Wasp's grub has eaten it.
Another of these splendid malefactors is decked in lapis-lazuli on the thorax and in Florentine bronze and gold on the abdomen, with a terminal scarf of azure. The nomenclators have christened her Stilbum calens, FAB. When Eumenes Amedei (1) has built on the rock her agglomeration of dome-shaped cells, with a casing of little pebbles set in the plaster, when the store of Caterpillars is consumed and the secluded ones have hung their apartments with silk, we see the Stilbum take her stand on the inviolable citadel. No doubt some imperceptible cranny, some defect in the cement, allows her to insert her ovipositor, which shoots out like a probe. At any rate, about the end of the following May, the Eumenes' chamber contains a cocoon which again is shaped like a thimble. From this cocoon comes a Stilbum calens. There is nothing left of the Eumenes' grub: the Golden Wasp has gorged herself upon it.
Flies play no small part in this brigandage. Nor are they the least to be dreaded, weaklings though they be, sometimes so feeble that the collector dare not take them in his fingers for fear of crushing them. There are some clad in velvet so extraordinarily delicate that the least touch rubs it off. They are fluffs of down almost as frail, in their soft elegance, as the crystalline edifice of a snowflake before it touches ground. They are called Bombylii.
With this fragility of structure is combined an incomparable power of flight. See this one, hovering motionless two feet above the ground. Her wings vibrate so rapidly that they appear to be in repose. The insect looks as though it were hung at one point in space by some invisible thread. You make a movement; and the Bombylius has disappeared. You cast your eyes in search of her around you, far away, judging the distance by the vigour of her flight. There is nothing here, nothing there. Then where is she? Close by you. Look at the point whence she started: the Bombylius is there again, hovering motionless. From this aerial observatory, as quickly recovered as quitted, she inspects the ground, watching for the favourable moment to establish her egg at the cost of another creature's destruction. What does she covet for her offspring: the honey-cupboard, the stores of game, the larvae in their transformation-sleep? I do not know yet, What I do know is that her slender legs and her dainty velvet dress do not allow her to make underground searches. When she has found the propitious place, suddenly she will swoop down, lay her egg on the surface in that lightning touch with the tip of her abdomen and straightway fly up again. What I suspect, for reasons set forth presently, is that the grub that comes out of the Bombylius' egg must, of its own motion, at its own risk and peril, reach the victuals which the mother knows to be close at hand. She has no strength to do more; and it is for the new-born grub to make its way into the refectory.
I am better acquainted with the manoeuvres of certain Tachinae, the tiniest of pale-grey Flies, who, cowering on the sand in the sun, in the neighbourhood of a burrow, patiently await the hour at which to strike the fell blow. Let a Bembex-wasp return from the chase, with her Gad-fly; a Philanthus, with her Bee; a Cerceris, with her Weevil; a Tachytes, with her Locust: straightway the parasites are there, coming and going, turning and twisting with the Wasp, always at her rear, without allowing themselves to be put off by any cautious feints. At the moment when the huntress goes indoors, with her captured game between her legs, they fling themselves on her prey, which is on the point of disappearing underground, and nimbly lay their eggs upon it. The thing is done in the twinkling of an eye: before the threshold is crossed, the carcase holds the germs of a new set of guests, who will feed on victuals not amassed for them and starve the children of the house to death.
This other, resting on the burning sand, is also a member of the Fly tribe; she is an Anthrax (2). She has wide wings, spread horizontally, half smoked and half transparent. She wears a dress of velvet, like the Bombylius, her near neighbour in the official registers; but, though the soft down is similar in fineness, it is very different in colour. Anthrax is Greek for coal. It is a happy denomination, reminding us of the Fly's mourning livery, a coal-black livery with silver tears. The same deep mourning garbs those parasitic Bees, and these are the only instances known to me of that violent opposition of dead black and white.
Nowadays, when men interpret everything with glorious assurance, when they explain the Lion's tawny mane as due to the colour of the African desert, attribute the Tiger's dark stripes to the streaks of shadow cast by the bamboos and extricate any number of other magnificent things with the same facility from the mists of the unknown, I should not be sorry to hear what they have to say of the Melecta, the Crocisa and the Anthrax and of the origin of their exceptional costume.
The word ‚mimesis‘ has been invented for the express purpose of designating the animal's supposed faculty of adapting itself to its environment by imitating the objects around it, at least in the matter of colouring. We are told that it uses this faculty to baffle its foes, or else to approach its prey without alarming it. Finding itself the better for this dissimulation, a source of prosperity indeed, each race, sifted by the struggle for life, is considered to have preserved those best-endowed with mimetic powers and to have allowed the others to become extinct, thus gradually converting into a fixed characteristic what at first was but a casual acquisition. The Lark became earth-coloured in order to hide himself from the eyes of the birds of prey when pecking in the fields; the Common Lizard adopted a grass-green tint in order to blend with the foliage of the thickets in which he lurks; the Cabbage-caterpillar guarded against the bird's beak by taking the colour of the plant on which it feeds. And so with the rest.
In my callow youth, these comparisons would have interested me: I was just ripe for that kind of science. In the evenings, on the straw of the threshing-floor, we used to talk of the Dragon, the monster which, to inveigle people and snap them up with greater certainty, became indistinguishable from a rock, the trunk of a tree, a bundle of twigs. Since those happy days of artless credulity, scepticism has chilled my imagination to some extent. By way of a parallel with the three examples which I have quoted, I ask myself why the White Wagtail, who seeks his food in the furrows as does the Lark, has a white shirt-front surmounted by a magnificent black stock. This dress is one of those most easily picked out at a distance against the rusty colour of the soil. Whence this neglect to practise mimesis, ‚protective mimicry‘? He has every need of it, poor fellow, quite as much as his companion in the fields!
Why is the Eyed Lizard of Provence as green as the Common Lizard, considering that he shuns verdure and chooses as his haunt, in the bright sunlight, some chink in the naked rocks where not so much as a tuft of moss grows? If, to capture his tiny prey, his brother in the copses and the hedges thought it necessary to dissemble and consequently to dye his pearl-embroidered coat, how comes it that the denizen of the sun-blistered rocks persists in his blue-and-green colouring, which at once betrays him against the whity-grey stone? Indifferent to mimicry, is he the less skilful Beetle-hunter on that account, is his race degenerating? I have studied him sufficiently to be able to declare with positive certainty that he continues to thrive both in numbers and in vigour.
Why has the Spurge-caterpillar adopted for its dress the gaudiest colours and those which contrast most with the green of the leaves which it frequents? Why does it flaunt its red, black and white in patches clashing violently with one another? Would it not be worth its while to follow the example of the Cabbage-caterpillar and imitate the verdure of the plant that feeds it? Has it no enemies? Of course it has: which of us, animals and men, has not?
A string of these whys could be extended indefinitely. It would give me amusement, did my time permit me, to counter each example of protective mimicry with a host of examples to the contrary. What manner of law is this which has at least ninety-nine exceptions in a hundred cases? Poor human nature! There is a deceptive agreement between a few actual facts and the theory which we are so foolishly ready to believe; and straightway we interpret the facts in the light of the theory. In a speck of the immense unknown we catch a glimpse of a phantom truth, a shadow, a will-o'-the-wisp; once the atom is explained, for better or worse, we imagine that we hold the explanation of the universe and all that it contains; and we forthwith shout:
‚The great law of Nature! Behold the infallible law!‘
Meanwhile, the discordant facts, an innumerable host, clamour at the gates of the law, being unable to gain admittance.
At the door of that infinitely restricted law clamour the great tribe of Golden Wasps, whose dazzling splendour, worthy of the wealth of Golconda, clashes with the dingy colour of their haunts. To deceive the eyes of their bird-tyrants, the Swift, the Swallow, the Chat and the others, these Chrysis-wasps, who glow like a carbuncle, like a nugget in the midst of its dark veinstone, certainly do not adapt themselves to the sand and the clay of their downs. The Green Grasshopper, we are told, thought out a plan for gulling his enemies by identifying himself in colour with the grass in which he dwells, whereas the Wasp, so rich in instinct and strategy, allowed herself to be distanced in the race by the dull-witted Locust! Rather than adapt herself as the other does, she persists in her incredible splendour, which betrays her from afar to every insect-eater and in particular to the little Grey Lizard, who lies hungrily in wait for her on the old sun-tapestried walls. She remains ruby, emerald and turquoise amidst her grey environment; and her race thrives none the worse.
The enemy that eats you is not the only one to be deceived; mimesis must also play its colour-tricks on him whom you have to eat. See the Tiger in his jungle, see the Praying Mantis on her green branch (3). Astute mimicry is even more necessary when the one to be duped is an amphitryon at whose cost the parasite's family is to be established. The Tachinae seem to declare as much: they are grey or greyish, of a colour as undecided as the dusty soil on which they cower while waiting for the arrival of the huntress laden with her capture. But they dissemble in vain: the Bembex, the Philanthus and the others see them from above, before touching ground; they recognize them perfectly at a distance, despite their grey costume. And so they hover prudently above the burrow and strive, by sudden feints, to mislead the traitorous little Fly, who, on her side, knows her business too well to allow herself to be enticed away or to leave the spot where the other is bound to return. No, a thousand times no: clay-coloured though they be, the Tachinae have no better chance of attaining their ends than a host of other parasites whose clothing is not of grey frieze to match the locality frequented, as witness the glittering Chrysis, or the Melecta and the Crocisa, with their white spots on a black ground.
We are also told that, the better to cozen his amphitryon, the parasite adopts more or less the same shape and colouring; he turns himself, in appearance, into a harmless neighbour, a worker belonging to the same guild. Instance the Psithyrus, who lives at the expense of the Bumble-bee. But in what, if you please, does Parnopes carnea resemble the Bembex into whose home she penetrates in her presence? In what does the Melecta resemble the Anthophora, who stands aside on her threshold to let her pass? The difference of costume is most striking. The Melecta's deep mourning has naught in common with the Anthophora's russet coat. The Parnopes' emerald-and-carmine thorax possesses not the least feature of resemblance with the black-and-yellow livery of the Bembex. And this Chrysis also is a dwarf in comparison with the ardent Nimrod who goes hunting Gad-flies.
Besides, what a curious idea, to make the parasite's success depend upon a more or less faithful likeness with the insect to be robbed! Why, the imitation would have exactly the opposite effect! With the exception of the Social Bees, who work at a common task, failure would be certain, for here, as among mankind, two of a trade never agree. An Osmia, an Anthophora, a Chalicodoma had better be careful not to poke an indiscreet head in at her neighbour's door: a sound drubbing would soon recall her to a sense of the proprieties. She might easily find herself with a dislocated shoulder or a mangled leg in return for a simple visit which was perhaps prompted by no evil intention. Each for herself in her own stronghold. But let a parasite appear, meditating foul play: that's a very different thing. She can wear the trappings of Harlequin or of a church-beadle; she can be the Clerus-beetle, in wing-cases of vermilion with blue trimmings, or the Dioxys-bee, with a red scarf across her black abdomen, and the mistress of the house will let her have her way, or, if she become too pressing, will drive her off with a mere flick of her wing. With her, there is no serious fray, no fierce fight. The Bludgeon is reserved for the friend of the family. Now go and practice your mimesis in order to receive a welcome from the Anthophora or the Chalicodoma! A few hours spent with the insects themselves will turn any one into a hardened scoffer at these artless theories.
To sum up, mimesis, in my eyes, is a piece of childishness. Were I not anxious to remain polite, I should say that it is sheer stupidity; and the word would express my meaning better. The variety of combinations in the domain of possible things is infinite. It is undeniable that, here and there, cases occur in which the animal harmonizes with surrounding objects. It would even be very strange if such cases were excluded from actuality, since everything is possible. But these rare coincidences are faced, under exactly similar conditions, by inconsistencies so strongly marked and so numerous that, having frequency on their side, they ought, in all logic, to serve as the basis of the law. Here, one fact says yes; there, a thousand facts say no. To which evidence shall we lend an ear? If we only wish to bolster up a theory, it would be prudent to listen to neither. The how and why escapes us; what we dignify with the pretentious title of a law is but a way of looking at things with our mind, a very squint-eyed way, which we adopt for the requirements of our case. Our would-be laws contain but an infinitesimal shade of reality; often indeed they are but puffed out with vain imaginings. Such is the law of mimesis, which explains the Green Grasshopper by the green leaves in which this Locust settles and is silent as to the Crioceris, that coral-red Beetle who lives on the no less green leaves of the lily.
And it is not only a mistaken interpretation: it is a clumsy pitfall in which novices allow themselves to be caught. Novices, did I say? The greatest experts themselves fall into the trap. One of our masters of entomology did me the honour to visit my laboratory. I was showing my collection of parasites. One of them, clad in black and yellow, attracted his attention.
‚This,‘ said he, ‚is obviously a parasite of the Wasps.‘
Surprised at the statement, I interposed:
‚By what signs do you know her?‘
‚Why look: it‘s the exact colouring of the Wasp, a mixture of black and yellow. It is a most striking case of mimesis.'
‚Just so; nevertheless, our black-and-yellow friend is a parasite of the Chalicodoma of the Walls, who has nothing in common, either in shape or colour, with the Wasp. This is a Leucopsis, not one of whom enters the Wasps‘ nest.'
‚Mimesis is an illusion which we should do well to relegate to oblivion.‘
And, with the evidence, a whole series of conclusive examples, in front of him, my learned visitor admitted with a good grace that his first convictions were based on a most ludicrous foundation.
A piece of advice to beginners: you will go wrong a thousand times for once that you are right if, when anxious to obtain a premature sight of the probable habits of an insect, you take mimesis as your guide. With mimesis above all, it is wise, when the law says that a thing is black, first to enquire whether it does not happen to be white.
Let us go on to more serious subjects and enquire into parasitism itself, without troubling any longer about the costume of the parasite. According to etymology, a parasite is one who eats another's bread, one who lives on the provisions of others. Entomology often alters this term from its real meaning. Thus it describes as parasites the Chrysis, the Mutilla, the Anthrax, the Leucopsis, all of whom feed their family not on the provisions amassed by others, but on the very larvae which have consumed those provisions, their actual property. When the Tachinae have succeeded in laying their eggs on the game warehoused by the Bembex, the burrower's home is invaded by real parasites, in the strict sense of the word. Around the heap of Gad-flies, collected solely for the children of the house, new guests force their way, numerous and hungry, and without the least ceremony plunge into the thick of it. They sit down to a table that was not laid for them; they eat side by side with the lawful owner; and this in such haste that he dies of starvation, though he is respected by the teeth of the interlopers who have gorged themselves on his portion.
When the Melecta has substituted her egg for the Anthophora's, here again we see a real parasite settling in the usurped cell. The pile of honey laboriously gathered by the mother will not even be broken in upon by the nurseling for which it was intended. Another will profit by it, with none to say him nay. Tachinae and Melectae: those are the true parasites, consumers of others' goods.
Can we say as much of the Chrysis or the Mutilla? In no wise. The Scoliae, whose habits are known to us, are certainly not parasites (4). No one will accuse them of stealing the food of others. Zealous workers, they seek and find under ground the fat grubs on which their family will feed. They follow the chase by virtue of the same quality as the most renowned hunters, Cerceris, Sphex or Ammophila; only, instead of removing the game to a special lair, they leave it where it is, down in the burrow. Homeless poachers, they let their venison be consumed on the spot where it is caught.
In what respect do the Mutilla, the Chrysis, the Leucopsis, the Anthrax and so many others differ, in their way of living, from the Scolia? It seems to me, in none. See for yourselves. By an artifice that varies according to the mother's talent, their grubs, either in the germ-stage or newly-born, are brought into touch with the victim that is to feed them: an unwounded victim, for most of them are without a sting; a live victim, but steeped in the torpor of the coming transformations and thus delivered without defence to the grub that is to devour it.
With them, as with the Scoliae, meals are made on the spot on game legitimately acquired by indefatigable battues or by patient stalking in which all the rules have been observed; only, the animal hunted is defenceless and does not need to be laid low with a dagger-thrust. To seek and find for one's larder a torpid prey incapable of resistance is, if you like, less meritorious than heroically to stab the strong-jawed Rose-chafer or Rhinoceros-beetle; but since when has the title of sportsman been denied to him who blows out the brains of a harmless Rabbit, instead of waiting without flinching for the furious charge of the Wild Boar and driving his hunting-knife into him behind his shoulder? Besides, if the actual assault is without danger, the approach is attended with a difficulty that increases the merit of these second-rate poachers. The coveted game is invisible. It is confined in the stronghold of a cell and moreover protected by the surrounding wall of a cocoon. Of what prowess must not the mother be capable to determine the exact spot at which it lies and to lay her egg on its side or at least close by? For these reasons, I boldly number the Chrysis, the Mutilla and their rivals among the hunters and reserve the ignoble title of parasites for the Tachina, the Melecta, the Crocisa, the Meloe-beetle, in short, for all those who feed on the provisions of others.
All things considered, is ignoble the right epithet to apply to parasitism? No doubt, in the human race, the idler who feeds at other people's tables is contemptible at all points; but must the animal bear the burden of the indignation inspired by our own vices? Our parasites, our scurvy parasites, live at their neighbour's expense: the animal never; and this changes the whole aspect of the question. I know of no instance, not one, excepting man, of parasites who consume the provisions hoarded by a worker of the same species. There may be, here and there, a few cases of larceny, of casual pillage among hoarders belonging to the same trade: that I am quite ready to admit, but it does not affect things. What would be really serious and what I formally deny is that, in the same zoological species, there should be some who possessed the attribute of living at the expense of the rest. In vain do I consult my memory and my notes: my long entomological career does not furnish me with a solitary example of such a misdeed as that of an insect leading the life of a parasite upon its fellows.
When the Chalicodoma of the Sheds works, in her thousands, at her Cyclopean edifice, each has her own home, a sacred home where not one of the tumultuous swarm, except the proprietress, dreams of taking a mouthful of honey. It is as though there were a neighbourly understanding to respect the others' rights. Moreover, if some heedless one mistakes her cell and so much as alights on the rim of a cup that does not belong to her, forthwith the owner appears, admonishes her severely and soon calls her to order. But, if the store of honey is the estate of some deceased Bee, or of some wanderer unduly prolonging her absence, then — and then alone — a kinswoman seizes upon it. The goods were waste property, which she turns to account; and it is a very proper economy. The other Bees and Wasps behave likewise: never, I say never, do we find among them an idler assiduously planning the conquest of her neighbour's possessions. No insect is a parasite on its own species.
What then is parasitism, if one must look for it among animals of different races? Life in general is but a vast brigandage. Nature devours herself; matter is kept alive by passing from one stomach into another. At the banquet of life, each is in turn the guest and the dish; the eater of to-day becomes the eaten of tomorrow; hodie tibi, cras mihi. Everything lives on that which lives or has lived; everything is parasitism. Man is the great parasite, the unbridled thief of all that is fit to eat. He steals the milk from the Lamb, he steals the honey from the children of the Bee, even as the Melecta pilfers the pottage of the Anthophora's sons. The two cases are similar. Is it the vice of indolence? No, it is the fierce law which for the life of the one exacts the death of the other.
In this implacable struggle of devourers and devoured, of pillagers and pillaged, of robbers and robbed, the Melecta deserves no more than we the title of ignoble; in ruining the Anthophora, she is but imitating man in one detail, man who is the infinite source of destruction. Her parasitism is no blacker than ours: she has to feed her offspring; and, possessing no harvesting-tools, ignorant besides of the art of harvesting, she uses the provisions of others who are better endowed with implements and talents. In the fierce riot of empty bellies, she does what she can with the gifts at her disposal.
1. A species of Mason-wasp.
2. Cf. „The Life of the Fly“: chapter 2.
3. For the Praying Mantis, cf. „Social Life in the Insect World“, by J.H. Fabre, translated by Bernard Miall: chapters 5 to 7.
4. The habits of the Scolia-wasp have been described in different essays not yet translated into English.