Chapter IX. The Theory of Parasitism
Jean-Henri Fabre Mason-bees
Cuckoo Bumble Bee (Psithyrus Insularis)
The Melecta does what she can with the gifts at her disposal. I should leave it at that, if I had not to take into consideration a grave charge brought against her. She is accused of having lost, for want of use and through laziness, the workman's tools with which, so we are told, she was originally endowed. Finding it to her advantage to do nothing, bringing up her family free of expense, to the detriment of others, she is alleged to have gradually inspired her race with an abhorrence for work. The harvesting-tools, less and less often employed, dwindled and perished as organs having no function; the species changed into a different one; and finally idleness turned the honest worker of the outset into a parasite. This brings us to a very simple and seductive theory of parasitism, worthy to be discussed with all respect. Let us set it forth.
Some mother, nearing the end of her labours and in a hurry to lay her eggs, found, let us suppose, some convenient cells provisioned by her fellows. There was no time for nest-building and foraging; if she would save her family, she must perforce appropriate the fruit of another's toil. Thus relieved of the tedium and fatigue of work, freed of every care but that of laying eggs, she left a progeny which duly inherited the maternal slothfulness and handed this down in its turn, in a more and more accentuated form, as generation followed on generation; for the struggle for life made this expeditious way of establishing yourself one of the most favourable conditions for the success of the offspring. At the same time, the organs of work, left unemployed, became atrophied and disappeared, while certain details of shape and colouring were modified more or less, so as to adapt themselves to the new circumstances. Thus the parasitic race was definitely established.
This race, however, was not too greatly transformed for us to be able, in certain cases, to trace its origin. The parasite has retained more than one feature of those industrious ancestors. So, for instance, the Psithyrus is extremely like the Bumble-bee, whose parasite and descendant she is. The Stelis preserves the ancestral characteristics of the Anthidium; the Coelioxys-bee recalls the Leaf-cutter.
Thus speak the evolutionists, with a wealth of evidence derived not only from correspondence in general appearance, but also from similarity in the most minute particulars. Nothing is small: I am as much convinced of that as any man; and I admire the extraordinary precision of the details furnished as a basis for the theory. But am I convinced? Rightly or wrongly, my turn of mind does not hold minutiae of structure in great favour: a joint of the palpi leaves me rather cold; a tuft of bristles does not appear to me an unanswerable argument. I prefer to question the creature direct and to let it describe its passions, its mode of life, its aptitudes. Having heard its evidence, we shall see what becomes of the theory of parasitism.
Before calling upon it to speak, why should I not say what I have on my mind? And mark me, first of all, I do not like that laziness which is said to favour the animal's prosperity. I have also believed and I still persist in believing that activity alone strengthens the present and ensures the future both of animals and men. To act is to live; to work is to go forward. The energy of a race is measured by the aggregate of its action.
No, I do not like it at all, this idleness so much commended of science. We have quite enough of these zoological brutalities: man, the son of the Ape; duty, a foolish prejudice; conscience, a lure for the simple; genius, neurosis; patriotism, jingo heroics; the soul, a product of protoplasmic energies; God, a puerile myth. Let us raise the war-whoop and go out for scalps; we are here only to devour one another; the summum bonum is the Chicago packer's dollar-chest! Enough, quite enough of that, without having transformism next to break down the sacred law of work. I will not hold it responsible for our moral ruin; it has not a sturdy enough shoulder to effect such a breach; but still it has done its worst.
No, once more, I do not like those brutalities which, denying all that gives some dignity to our wretched life, stifle our horizon under an extinguisher of matter. Oh, don't come and forbid me to think, though it were but a dream, of a responsible human personality, of conscience, of duty, of the dignity of labour! Everything is linked together: if the animal is better off, as regards both itself and its race, for doing nothing and exploiting others, why should man, its descendant, show greater scruples? The principle that idleness is the mother of prosperity would carry us far indeed. I have said enough on my own account; I will call upon the animals themselves, more eloquent than I.
Are we so very sure that parasitic habits come from a love of inaction? Did the parasite become what he is because he found it excellent to do nothing? Is repose so great an advantage to him that he abjured his ancient customs in order to obtain it? Well, since I have been studying the Bee who endows her family with the property of others, I have not yet seen anything in her that points to slothfulness. On the contrary, the parasite leads a laborious life, harder than that of the worker. Watch her on a slope blistered by the sun. How busy she is, how anxious! How briskly she covers every inch of the radiant expanse, how indefatigable she is in her endless quests; in her visits, which are generally fruitless! Before coming upon a nest that suits her, she has dived a hundred times into cavities of no value, into galleries not yet victualled. And then, however kindly her host, the parasite is not always well received in the hostelry. No, it is not all roses in her trade. The expenditure of time and labour which she finds necessary in order to house an egg may easily equal or even exceed that of the worker in building her cell and filling it with honey. That industrious one has regular and continuous work, an excellent condition for success in her egg-laying; the other has a thankless and precarious task, at the mercy of a thousand accidents which endanger the great undertaking of installing the eggs. One has only to watch the prolonged hesitation of a Coelioxys seeking for the Leaf-cutters' cells to recognize that the usurpation of another's nest is not effected without serious difficulties. If she turned parasite in order to make the rearing of her offspring easier and more prosperous, certainly she was very ill-inspired. Instead of rest, hard work; instead of a flourishing family, a meagre progeny.
To generalities, which are necessarily vague, we will add some precise facts. A certain Stelis (Stelis nasuta, LATR.) is a parasite of the Mason-bee of the Walls. When the Chalicodoma has finished building her dome of cells upon her pebble, the parasite appears, makes a long inspection of the outside of the home and proposes, puny as she is, to introduce her eggs into this cement fortress. Everything is most carefully closed: a layer of rough plaster, at least two-fifths of an inch thick, entirely covers the central accumulation of cells, which are each of them sealed with a thick mortar plug. And it is the honey of these well-guarded chambers that has to be reached by piercing a wall almost as hard as rock.
The parasite pluckily sets to; the idler becomes a glutton for work. Atom by atom, she perforates the general enclosure and scoops out a shaft just sufficient for her passage; she reaches the lid of the cell and gnaws it until the coveted provisions appear in sight. It is a slow and painful process, in which the feeble Stelis wears herself out, for the mortar is much the same as Roman cement in hardness. I myself find a difficulty in breaking it with the point of my knife. What patient effort, then, the task requires from the parasite, with her tiny pincers!
I do not know exactly how long the Stelis takes to make her entrance-shaft, as I have never had the opportunity or rather the patience to follow the work from start to finish; but what I do know is that a Chalicodoma of the Walls, incomparably larger and stronger than the parasite, when demolishing before my eyes the lid of a cell sealed only the day before, was unable to complete her undertaking in one afternoon. I had to come to her assistance in order to discover, before the end of the day, the object of her housebreaking. When the Mason-bee's mortar has once set, its resistance is that of stone. Now the Stelis has not only to pierce the lid of the honey-store; she must also pierce the general casing of the nest. What a time it must take her to get through such a task, a gigantic one for her poor tools!
It is done at last, after infinite labour. The honey appears. The Stelis slips through and, on the surface of the provisions, side by side with the Chalicodoma's eggs, the number varying from time to time. The victuals will be the common property of all the new arrivals, whether the son of the house or strangers.
The violated dwelling cannot remain as it is, exposed to marauders from without; the parasite must herself wall up the breach which she has contrived. The quondam housebreaker becomes a builder. At the foot of the pebble, the Stelis collects a little of that red earth which characterizes our stony plateaus grown with lavender and thyme; she makes it into mortar by wetting it with saliva; and with the pellets thus prepared she fills up the entrance-shaft, displaying all the care and art of a regular master-mason. Only, the work clashes in colour with the Chalicodoma's. The Bee goes and gathers her cementing-powder on the adjoining high-road, the metal of which consists of broken flint-stones, and very seldom uses the red earth under the pebble supporting the nest. This choice is apparently dictated by the fact that the chemical properties of the former are more likely to produce a solid structure. The lime of the road, mixed with saliva, yields a harder cement than red clay would do. At any rate, the Chalicodoma's nest is more or less white because of the source of its materials. When a red speck, a few millim?tres wide, appears on this pale background, it is a sure sign that a Stelis has been that way. Open the cell that lies under the red stain: we shall find the parasite's numerous family established there. The rusty spot is an infallible indication that the dwelling has been violated: at least, it is so in my neighbourhood, where the soil is as I have described.
We see the Stelis, therefore, at first a rabid miner, using her mandibles against the rock; next a kneader of clay and a plasterer restoring broken ceilings. Her trade does not seem one of the least arduous. Now what did she do before she took to parasitism? Judging from her appearance, the transformists tell us that she was an Anthidium, that is to say, she used to gather the soft cotton-wool from the dry stalks of the lanate plants and fashion it into wallets, in which to heap up the pollen-dust which she gleaned from the flowers by means of a brush carried on her abdomen. Or else, springing from a genus akin to the cotton-workers, she used to build resin partitions in the spiral stairway of a dead Snail. Such was the trade driven by her ancestors.
Really! So, to avoid slow and painful work, to achieve an easy life, to give herself the leisure favourable to the settlement of her family, the erstwhile cotton-presser or collector of resin-drops took to gnawing hardened cement! She who once sipped the nectar of flowers made up her mind to chew concrete! Why, the poor wretch toils at her filing like a galley-slave! She spends more time in ripping up a cell than it would take her to make a cotton wallet and fill it with food. If she really meant to progress, to do better in her own interest and that of her family, by abandoning the delicate occupations of the old days, we must confess that she has made a strange mistake. The mistake would be no greater if fingers accustomed to fancy-weaving were to lay aside velvet and silk and proceed to handle the quarryman's blocks or to break stones on the roadside.
No, the animal does not commit the folly of voluntarily embittering its lot; it does not, in obedience to the promptings of idleness, give up one condition to embrace another and a more irksome; should it blunder for once, it will not inspire its posterity with a wish to persevere in a costly delusion. No, the Stelis never abandoned the delicate art of cotton-weaving to break down walls and to grind cement, a class of work far too unattractive to efface the memory of the joys of harvesting amid the flowers. Indolence has not evolved her from an Anthidium. She has always been what she is to-day: a patient artificer in her own line, a steady worker at the task that has fallen to her share.
That hurried mother who first, in remote ages, broke into the abode of her fellows to secure a home for her eggs found this unscrupulous method, so you tell us, very favourable to the success of her race, by virtue of its economy of time and trouble. The impression left by this new policy was so profound that heredity bequeathed it to posterity, in ever-increasing proportions, until at last parasitic habits became definitely fixed. The Chalicodoma of the Sheds, followed by the Three-horned Osmia, will teach us what to think of this conjecture.
I have described in an earlier chapter my installation of Chalicodoma-hives against the walls of a porch facing the south. Here, on a level with my head, placed so that they can easily be observed, hang some tiles removed from the neighbouring roofs in winter, together with their enormous nests and their occupants. Every May, for five or six years in succession, I have assiduously watched the works of my Mason-bees. From the mass of my notes on the subject I take the following experiments which bear upon the matter under discussion.
Long ago, when I used to scatter a handful of Chalicodomae some way from home, in order to study their capacity for finding their nest again, I noticed that, if they were too long absent, the laggards found their cells closed on their return. Neighbours had taken the opportunity to lay their eggs there, after finishing the building and stocking it with provisions. The abandoned property benefited another. On realizing the usurpation, the Bee returning from her long journey soon consoled herself for the mishap. She began to break the seals of some cell or other, adjoining her own; the rest let her have her way, being doubtless too busy with their present labours to seek a quarrel with the freebooter. As soon as she had destroyed the lid, the Bee, with a sort of feverish haste that burned to repay theft by theft, did a little building, did a little victualling, as though to resume the thread of her occupations, destroyed the egg in being, laid her own and closed the cell again. Here was a touch of nature that deserved careful examination.
At eleven o'clock in the morning, when the work is at its height, I mark half-a-score of Chalicodomae with different colours, to distinguish them from one another. Some are occupied with building, others are disgorging honey. I mark the corresponding cells in the same way. As soon as the marks are quite dry, I catch the ten Bees, place them singly in screws of paper and shut them all in a box until the next morning. After twenty-four hours' captivity, the prisoners are released. During their absence, their cells have disappeared under a layer of recent structures; or, if still exposed to view, they are closed and others have made use of them.
As soon as they are free, the ten Bees, with one exception, return to their respective tiles. They do more than this, so accurate is their memory, despite the confusion resulting from a prolonged incarceration: they return to the cell which they have built, the beloved stolen cell; they minutely explore the outside of it, or at least what lies nearest to it, if the cell has disappeared under the new structures. In cases where the home is not henceforward inaccessible, it is at least occupied by a strange egg and the door is securely fastened. To this reverse of fortune the ousted ones retort with the brutal lex talionis: an egg for an egg, a cell for a cell. You've stolen my house; I'll steal yours. And, without much hesitation, they proceed to force the lid of a cell that suits them. Sometimes they recover possession of their own home, if it is possible to get into it; sometimes and more frequently they seize upon some one else's, even at a considerable distance from their original dwelling.
Patiently they gnaw the mortar lid. As the general rough-cast covering all the cells is not applied until the end of the work, all that they need do is to demolish the lid, a hard and wearisome task, but not beyond the strength of their mandibles. They therefore attack the door, the cement disk, and reduce it to dust. The criminal is allowed to carry out her nefarious designs without the slightest interference or protest from any of her neighbours, though these must necessarily include the chief party interested. The Bee is as forgetful of her cell of yesterday as she is jealous of her actual cell. To her the present is everything; the past means nothing; and the future means no more. And so the population of the tile leave the breakers of doors to do their business in peace; none hastens to the defence of a home that might well be her own. How differently things would happen if the cell were still on the stocks! But it dates back to yesterday, to the day before; and no one gives it another thought.
It's done: the lid is demolished; access is free. For some time, the Bee stands bending over the cell, her head half-buried in it, as though in contemplation. She goes away, she returns undecidedly; at last she makes up her mind. The egg is snapped up from the surface of the honey and flung on the rubbish-heap with no more ceremony than if the Bee were ridding the house of a bit of dirt. I have witnessed this hideous crime again and yet again; I confess to having repeatedly provoked it. In housing her egg, the Mason-bee displays a brutal indifference to the fate of her neighbour's egg.
I see some of them afterwards busy provisioning, disgorging honey and brushing pollen into the cell already completely provisioned; I see some masoning a little at the orifice, or at least laying on a few trowels of mortar. It seems as if the Bee, although the victuals and the building are just as they should be, were resuming the work at the point at which she left it twenty-four hours before. Lastly, the egg is laid and the opening closed up. Of my captives, one, less patient than the rest, rejects the slow process of eating away the cover and decides in favour of robbery with violence, on the principle that might is right. She dislodges the owner of a half-stocked cell, keeps good watch for a long time on the threshold of the home and, when she feels herself the mistress of the house, goes on with the provisioning. I follow the ousted proprietress with my eyes. I see her seize upon a closed cell by breaking into it, behaving in all respects like my imprisoned Chalicodomae.
The whole occurrence was too significant to be left without further confirmation. I repeated the experiment, therefore, almost every year, always with the same success. I can only add that, among the Bees placed by my artifices under the necessity of making up for lost time, a few are of a more easy-going temperament. I see some building anew, as if nothing out of the way had happened; others — this is a very rare course — going to settle on another tile, as though to avoid a society of thieves; and lastly a few who bring pellets of mortar and zealously finish the lid of their own cell, although it contains a strange egg. However, housebreaking is the usual thing.
One more detail not without value: it is not necessary for you to intervene and imprison Mason-bees for a time in order to witness the acts of violence which I have described. If you follow the work of the swarm assiduously, you may occasionally find a surprise awaiting you. A Mason-bee will appear and, for no reason known to you, break open a door and lay her egg in the violated cell. From what goes before, I look upon the Bee as a laggard, kept away from the workyard by an accident, or else carried to a distance by a gust of wind. On returning after an absence of some duration, she finds her place taken, her cell used by another. The victim of an usurper's villainy, like the prisoners in my paper screws, she behaves as they do and indemnifies herself for her loss by breaking into another's home.
Lastly, it was a matter of learning the behaviour, after their act of violence, of the Masons who have smashed in a door, brutally expelled the egg within and replaced it by one of their own laying. When the lid is repaired to look as good as new and everything restored to order, will they continue their burglarious ways and exterminate the eggs of others to make room for their own? By no means. Revenge, that pleasure of the gods and perhaps also of Bees, is satisfied after one cell has been ripped open. All anger is appeased when the egg for which so much work has been done is safely housed. Henceforth, both prisoners and stray laggards resume their ordinary labours, indifferently with the rest. They build honestly, they provision honestly, nor meditate further evil. The past is quite forgotten until a fresh disaster occurs.
To return to the parasites: a mother chanced to find herself the mistress of another's nest. She took advantage of this to entrust her egg to it. This expeditious method, so easy for the mother and so favourable to the success of her offspring, made such an impression on her that she transmitted the maternal indolence to her posterity. Thus the worker gradually became transformed into a parasite.
Capital! The thing goes like clockwork, as long as we have only to put our ideas on paper. But let us just consult the facts, if you don't mind; before arguing about probabilities, let us look into things as they are. Here is the Mason-bee of the Sheds teaching us something very curious. To smash the lid of a cell that does not belong to her, to throw the egg out of doors and put her own in its place is a practice which she has followed since time began. There is no need of my interference to make her commit burglary: she commits it of her own accord, when her rights are prejudiced as the result of a too-long absence. Ever since her race has been kneading cement, she has known the law of retaliation. Countless ages, such as the evolutionists require, have made her adopt forcible usurpation as an inveterate habit. Moreover, robbery is so incomparably easy for the mother. No more cement to scratch up with her mandibles on the hard ground, no more mortar to knead, no more clay walls to build, no more pollen to gather on hundreds and hundreds of journeys. All is ready, board and lodging. Never was a better opportunity for allowing one's self a good time. There is nothing against it. The others, the workers, are imperturbable in their good-humour. Their outraged cells leave them profoundly indifferent. There are no brawls to fear, no protests. Now or never is the moment to tread the primrose path.
Besides, your progeny will be all the better for it. You can choose the warmest and wholesomest spots; you can multiply your laying-operations by devoting to them all the time that you would have to spend on irksome occupations. If the impression produced by the violent seizure of another's property is strong enough to be handed down by heredity, how deep should be the impression of the actual moment when the Mason-bee is in the first flush of success! The precious advantage is fresh in the memory, dating from that very instant; the mother has but to continue in order to create a method of installation favourable in the highest degree to her and hers. Come, poor Bee! Throw aside your exhausting labours, follow the evolutionists' advice and, as you have the means at your disposal, become a parasite!
But no, having effected her little revenge, the builder returns to her masonry, the gleaner to her gleaning, with unquenchable zeal. She forgets the crime committed in a moment of anger and takes good care not to hand down any tendency towards idleness to her offspring. She knows too well that activity is life, that work is the world's great joy. What myriads of cells has she not broken open since she has been building; what magnificent opportunities, all so clear and conclusive, has she not had to emancipate herself from drudgery! Nothing could convince her: born to work, she persists in an industrious life. She might at least have produced an offshoot, a race of housebreakers, who would invade cells by demolishing doors. The Stelis does something of the kind; but who would think of proclaiming a relationship between the Chalicodoma and her? The two have nothing in common. I call for a scion of the Mason-bee of the Sheds who shall live by the art of breaking through ceilings. Until they show me one, the theorists will only make me smile when they talk to me of erstwhile workers relinquishing their trade to become parasitic sluggards.
I also call, with no less insistence, for a descendant of the Three-horned Osmia, a descendant given to demolishing party-walls. I will describe later how I managed to make a whole swarm of these Osmiae build their nests on the table in my study, in glass tubes that enabled me to see the inmost secrets of the work of the Bee (1). For three or four weeks, each Osmia is scrupulously faithful to her tube, which is laboriously filled with a set of chambers divided by earthen partitions. Marks of different colours painted on the thorax of the workers enable me to recognize individuals in the crowd. Each crystal gallery is the exclusive property of one Osmia; no other enters it, builds in it or hoards in it. If, through heedlessness, through momentary forgetfulness of her own house in the tumult of the city, some neighbour so much as comes and looks in at the door, the owner soon puts her to flight. No such indiscretion is tolerated. Every Bee has her home and every home its Bee.
All goes well until just before the end of the work. The tubes are then closed at the orifice with a thick plug of earth; nearly the whole swarm has disappeared; there remain on the spot a score of tatterdemalions in threadbare fleeces, worn out by a month's hard toil. These laggards have not finished their laying. There is no lack of unoccupied tubes, for I take care to remove some of those which are full and to replace them by others that have not yet been used. Very few of the Bees decide to take possession of these new homes, which differ in no particular from the earlier ones; and even then they build only a small number of cells, which are often mere attempts at partitions.
They want something different: a nest belonging to some one else. They bore through the stopper of the inhabited tubes, a work of no great difficulty, for we have here not the hard cement of the Chalicodoma, but a simple lid of dried mud. When the entrance is cleared, a cell appears, with its store of provisions and its egg, with her brutal mandibles; she rips it open and goes and flings it away. She does worse: she eats it on the spot. I had to witness this horror many times over before I could accept it as a fact. Note that the egg devoured may very well contain the criminal's own offspring. Imperiously swayed by the needs of her present family, the Osmia puts her past family entirely out of her mind.
Having perpetrated this child-murder, the depraved creature does a little provisioning. They all experience the same necessity to go backwards in the sequence of actions in order to pick up the thread of their interrupted occupations. Her next work is to lay her egg and then she conscientiously restores the demolished lid.
The havoc can be more sweeping still. One of these laggards is not satisfied with a single cell; she needs two, three, four. To reach the most remote, the Osmia wrecks all those which come before it. The partitions are broken down, the eggs eaten or thrown away, the provisions swept outside and often even carried to a distance in great lumps. Covered with dust from the loose plaster of the demolition, floured all over with the rifled pollen, sticky with the contents of the mangled eggs, the Osmia, while at her brigand's work, is altered beyond recognition. Once the place is cleared, everything resumes its normal course. Provisions are laboriously brought to take the place of those which have been thrown away; eggs are laid, one on each heap of food; the partitions are built up again; and the massive plug sealing the whole structure is made as good as new.
Crimes of this kind recur so often that I am obliged to interfere and place in safety the nests which I wish to keep intact. And nothing as yet explains this brigandage, bursting forth at the end of the work like a moral epidemic, like a frenzied delirium. I should say nothing if the site were lacking; but the tubes are there, close by, empty and quite fit to receive the eggs. The Osmia refuses them, she prefers to plunder. Is it from weariness, from a distaste for work after a period of fierce activity? Not at all; for, when a row of cells has been stripped of its contents, after the ravage and waste, she has to come back to ordinary work, with all its burdens. The labour is not reduced; it is increased. It would pay the Bee infinitely better, if she wants to continue her laying, to make her home in an unoccupied tube. The Osmia thinks differently. Her reasons for acting as she does escape me. Can there be ill-conditioned characters among her, characters that delight in a neighbour's ruin? There are among men.
In the privacy of her native haunts, the Osmia, I have no doubt, behaves as in my crystal galleries. Towards the end of the building-operations, she violates others' dwellings. By keeping to the first cell, which it is not necessary to empty in order to reach the next, she can utilize the provisions on the spot and shorten to that extent the longest part of her work. As usurpations of this kind have had ample time to become inveterate, to become inbred in the race, I ask for a descendant of the Osmia who eats her grandmother's egg in order to establish her own egg.
This descendant I shall not be shown; but I may be told that she is in process of formation. The outrages which I have described are preparing a future parasite. The transformists dogmatize about the past and dogmatize about the future, but as seldom as possible talk to us about the present. Transformations have taken place, transformations will take place; the pity of it is that they are not actually taking place. Of the three tenses, one is lacking, the very one which directly interests us and which alone is clear of the incubus of theory. This silence about the present does not please me overmuch, scarcely more than the famous picture of „The Crossing of the Red Sea“ painted for a village chapel. The artist had put upon the canvas a broad ribbon of brightest scarlet; and that was all.
‚Yes, that‘s the Red Sea,' said the priest, examining the masterpiece before paying for it. ‚That‘s the Red Sea, right enough; but where are the Israelites?'
‚They have passed,‘ replied the painter.
‚And the Egyptians?‘
‚They are on the way.‘
Transformations have passed, transformations are on the way. For mercy's sake, cannot they show us transformations in the act? Must the facts of the past and the facts of the future necessarily exclude the facts of the present? I fail to understand.
I call for a descendant of the Chalicodoma and a descendant of the Osmia who have robbed their neighbours with gusto, when occasion offered, since the origin of their respective races, and who are working industriously to create a parasite happy in doing nothing. Have they succeeded? No. Will they succeed? Yes, people maintain. For the moment, nothing. The Osmiae and Chalicodomae of to-day are what they were when the first trowel of cement or mud was mixed. Then how many ages does it take to form a parasite? Too many, I fear, for us not to be discouraged.
If the sayings of the theorists are well-founded, going on strike and living by shifts was not always enough to assure parasitism. In certain cases, the animal must have had to change its diet, to pass from live prey to vegetarian fare, which would entirely subvert its most essential characteristics. What should we say to the Wolf giving up mutton and browsing on grass, in obedience to the dictates of idleness? The boldest would shrink from such an absurd assumption. And yet transformism leads us straight to it.
Here is an example: in July, I split some bramble-stems in which Osmia tridentata has built her nests. In the long series of cells, the lower already hold the Osmia's cocoons, while the upper contain the larva which has nearly finished consuming its provisions and the topmost show the victuals untouched, with the Osmia's egg upon them. It is a cylindrical egg, rounded at both extremities, of a transparent white and measuring four to five millim?tres in length (2). It lies slantwise, one end of it resting on the food and the other sticking up at some distance above the honey. Now, by multiplying my visits to the fresh cells, I have on several occasions made a very valuable discovery. On the free end of the Osmia's egg, another egg is fixed; an egg quite different in shape, white and transparent like the first, but much smaller and narrower, blunt at one end and tapering into a rather sharp point at the other. It is two millim?tres long by half a millim?tre wide (3). It is undeniably the egg of a parasite, a parasite which compels my attention by its curious method of installing its family.
It opens before the Osmia's egg. The tiny grub, as soon as it is born, begins to drain the rival egg, of which it occupied the top part, high up above the honey. The extermination soon becomes perceptible. You can see the Osmia's egg turning muddy, losing its brilliancy, becoming limp and wrinkled. In twenty-four hours, it is nothing but an empty sheath, a crumpled bit of skin. All competition is now removed; the parasite is the master of the house. The young grub, when demolishing the egg, was active enough: it explored the dangerous thing which had to be got rid of quickly, it raised its head to select and multiply the attacking-points. Now, lying at full length on the surface of the honey, it no longer shifts its position; but the undulations of the digestive canal betray its greedy absorption of the Osmia's store of food. The provisions are finished in a fortnight and the cocoon is woven. It is a fairly firm ovoid, of a very dark-brown colour, two characteristics which at once distinguish it from the Osmia's pale, cylindrical cocoon. The hatching takes place in April or May. The puzzle is solved at last: the Osmia's parasite is a Wasp called the Spotted Sapyga (Sapyga punctata, V.L.)
Now where are we to class this Wasp, a true parasite in the strict sense of the word, that is to say, a consumer of others' provisions. Her general appearance and her structure make it clear to any eye more or less familiar with entomological shapes that she belongs to a species akin to that of the Scoliae. Moreover, the masters of classification, so scrupulous in their comparison of characteristics, agree in placing the Sapygae immediately after the Scoliae and a little before the Mutillae. The Scoliae feed their grubs on prey; so do the Mutillae. The Osmia's parasite, therefore, if it really derives from a transformed ancestor, is descended from a flesh-eater, though it is now an eater of honey. The Wolf does more than become a Sheep: he turns himself into a sweet-tooth.
‚You will never get an apple-tree out of an acorn,‘ Franklin tells us, with that homely common-sense of his.
In this case, the passion for jam must have sprung from a love of venison. Any theory might well be deficient in balance when it leads to such vagaries as this.
I should have to write a volume if I would go on setting forth my doubts. I have said enough for the moment. Man, the insatiable enquirer, hands down from age to age his questions about the whys and wherefores of origins. Answer follows answer, is proclaimed true to-day and recognized as false tomorrow; and the goddess Isis continues veiled.
1. Cf. „Bramble-bees and Others“, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chapters 1 to 7.
2. .156 to .195 inch.
3. .078 and .019 inch.