Chapter V. The Problem of The Scoliae
Jean-Henri Fabre More Hunting Wasp
Now that all the facts have been set forth, it is time to collate them. We already know that the Beetle-hunters, the Cerceres (1), prey exclusively on the Weevils and the Buprestes, that is, on the families whose nervous system presents a degree of concentration which may be compared with that of the Scolia's victims. Those predatory insects, working in the open air, are exempt from the difficulties which their emulators, working underground, have to overcome. Their movements are free and are directed by the sense of sight; but their surgery is confronted in another respect with a most arduous problem.
The victim, a Beetle, is covered at all points with a suit of armour which the sting is unable to penetrate. The joints alone will allow the poisoned lancet to pass. Those of the legs do not in any way comply with the conditions imposed: the result of stinging them would be merely a partial disorder which far from subduing the insect, would render it more dangerous by irritating it yet further. A sting in the joint of the neck is not admissible: it would injure the cervical ganglia and lead to death, followed by putrefaction. There remains only the joint between the corselet and the abdomen.
The sting, in entering here, has to abolish all movement with a single stab, for any movement would imperil the rearing of the larva. The success of the paralysis, therefore, demands that the motor ganglia, at least the three thoracic ganglia, shall be packed in close contact opposite this point. This determines the selection of Weevils and Buprestes, both of which are so strongly armoured.
But where the prey has only a soft skin, incapable of stopping the sting, the concentrated nervous system is no longer necessary, for the operator, versed in the anatomical secrets of her victim, knows to perfection where the centres of innervation lie; and she wounds them one after another, if need be from the first to the last. Thus do the Ammophilae go to work when dealing with their caterpillars and the Sphex-wasps when dealing with their Locusts, Ephippigers and Crickets.
With the Scoliae we come once again to a soft prey, with a skin penetrable by the sting no matter where it be attacked. Will the tactics of the caterpillar-hunters, who stab and stab again, be repeated here? No, for the difficulty of movement under ground prohibits so complicated an operation. Only the tactics of the paralysers of armour-clad insects are practicable now, for, since there is but one thrust of the dagger, the feat of surgery is reduced to its simplest terms, a necessary consequence of the difficulties of an underground operation. The Scoliae, then, whose destiny it is to hunt and paralyse under the soil the victuals for their family, require a prey made highly vulnerable by the close assemblage of the nerve-centres, as are the Weevils and Buprestes of the Cerceres; and this is why it has fallen to their lot to share among them the larvae of the Scarabaeidae.
Before they obtained their allotted portion, so closely restricted and so judiciously selected; before they discovered the precise and almost mathematical point at which the sting must enter to produce a sudden and a lasting immobility; before they learnt how to consume, without incurring the risk of putrefaction, so corpulent a prey: in brief, before they combined these three conditions of success, what did the Scoliae do?
The Darwinian school will reply that they were hesitating, essaying, experimenting. A long series of blind gropings eventually hit upon the most favourable combination, a combination henceforth to be perpetuated by hereditary transmission. The skilful co-ordination between the end and the means was originally the result of an accident.
Chance! A convenient refuge! I shrug my shoulders when I hear it invoked to explain the genesis of an instinct so complex as that of the Scoliae. In the beginning, you say, the creature gropes and feels its way; there is nothing settled about its preferences. To feed its carnivorous larvae it levies tribute on every species of game which is not too much for the huntress' power or the nurseling's appetite; its descendants try now this, now that, now something else, at random, until the accumulated centuries lead to the selection which best suits the race. Then habit grows fixed and becomes instinct.
Very well. Let us agree that the Scolia of antiquity sought a different prey from that adopted by the modern huntress. If the family throve upon a diet now discontinued, we fail to see that the descendants had any reason to change it: animals have not the gastronomic fancies of an epicure whom satiety makes difficult to please. Because the race did well upon this fare, it became habitual; and instinct became differently fixed from what it is to-day. If, on the other hand, the original food was unsuitable, the existence of the family was jeopardized; and any attempt at future improvement became impossible, because an unhappily inspired mother would leave no heirs.
To escape falling into this twofold trap, the theorists will reply that the Scoliae are descended from a precursor, an indeterminate creature, of changeable habits and changing form, modifying itself in accordance with its environment and with the regional and climatic conditions and branching out into races each of which has become a species with the attributes which distinguish it to-day. The precursor is the deus ex machina of evolution. When the difficulty becomes altogether too importunate, quick, a precursor, to fill up the gaps, quick, an imaginary creature, the nebulous plaything of the mind! This is seeking to lighten the darkness with a still deeper obscurity; to illumine the day by piling cloud upon cloud. Precursors are easier to find than sound arguments. Nevertheless, let us put the precursor of the Scoliae to the test.
What did she do? Being capable of everything, she did a bit of everything. Among its descendants were innovators who developed a taste for tunnelling in sand and vegetable mould. There they encountered the larvae of the Cetonia, the Oryctes, the Anoxia, succulent morsels on which to rear their families. By degrees the indeterminate Wasp adopted the sturdy proportions demanded by underground labour. By degrees she learnt to stab her plump neighbours in scientific fashion; by degrees she acquired the difficult art of consuming her prey without killing it; at length, by degrees, aided by the richness of her diet, she became the powerful Scolia with whom we are familiar. Having reached this point, the species assumes a permanent form, as does its instinct.
Here we have a multiplicity of stages, all of the slowest, all of the most incredible nature, whereas the Wasp cannot found a race except on the express condition of complete success from the first attempt. We will not insist further upon the insurmountable objection; we will admit that, amid so many unfavourable chances, a few favoured individuals survive, becoming more and more numerous from one generation to the next, in proportion as the dangerous art of rearing the young is perfected. Slight variations in one and the same direction form a definite whole; and at long last the ancient precursor has become the Scolia of our own times.
By the aid of a vague phraseology which juggles with the secret of the centuries and the unknown things of life, it is easy to build up a theory in which our mental sloth delights, after being discouraged by difficult researches whose final result is doubt rather than positive statement. But if, so far from being satisfied with hazy generalities and adopting as current coin the terms consecrated by fashion, we have the perseverance to explore the truth as far as lies in our power, the aspect of things will undergo a great change and we shall discover that they are far less simple than our overprecipitate views declared them to be. Generalization is certainly a most valuable instrument: science indeed exists only by virtue of it. Let us none the less beware of generalizations which are not based upon very firm and manifold foundations.
When these foundations are lacking, the child is the great generalizer. For him, the feathered world consists merely of birds; the race of reptiles merely of snakes, the only difference being that some are big and some are little. Knowing nothing, he generalizes in the highest degree; he simplifies, in his inability to perceive the complex. Later he will learn that the Sparrow is not the Bullfinch, that the Linnet is not the Greenfinch; he will particularize and to a greater degree each day, as his faculty of observation becomes more fully trained. In the beginning he saw nothing but resemblances; he now sees differences, but still not plainly enough to avoid incongruous comparisons.
In his adult years he will almost to a certainty commit zoological blunders similar to those which my gardener retails to me. Favier, an old soldier, has never opened a book, for the best of reasons. He barely knows how to cipher: arithmetic rather than reading is forced upon us by the brutalities of life. Having followed the flag over three-quarters of the globe, he has an open mind and a memory crammed with reminiscences, which does not prevent him, when we chat about animals, from making the most crazy assertions. For him the Bat is a Rat that has grown wings; the Cuckoo is a Sparrow-hawk retired from business; the Slug is a Snail who has lost his shell with the advance of years; the Nightjar (2), the Chaoucho-grapaou, as he calls her, is an elderly Toad, who, becoming enamoured of milk-food, has grown feathers, so that she may enter the byres and milk the Goats. It is impossible to drive these fantastic ideas out of his head. Favier himself, as will be seen, is an evolutionist after his own fashion, an evolutionist of a very daring type. In accounting for the origin of animals nothing gives him pause. He has a reply to everything: „this“ comes from „that.“ If you ask him why, he answers:
„Look at the resemblance!“
Shall we reproach him with these insanities, when we hear another, misled by the Monkey's build, acclaim the Pithecanthropus as man's precursor? Shall we reject the metamorphosis of the Chaoucho-grapaou, when people tell us in all seriousness that, in the present stage of scientific knowledge, it is absolutely proved that man is descended from some rough-hewn Ape? Of the two transformations, Favier's strikes me as the more credible. A painter of my acquaintance, a brother of the great composer F?licien David (3), favoured me one day with his reflections on the human structure:
„Ve, moun bel ami,“ he said. „Ve, l'home a lou dintre d'un por et lou defero d'uno mounino.“ „See, my dear friend, see: man has the inside of a pig and the outside of a monkey.“
I recommend the painter's aphorism to those who might like to discover man's origin in the Hog when the Ape has gone out of fashion. According to David, descent is proved by internal resemblances:
„L'home a lou dintre d'un por.“
The inventory of precursory types sees nothing but organic resemblances and disdains the differences of aptitude. By consulting only the bones, the vertebrae, the hair, the nervures of the wings, the joints of the antennae, the imagination may build up any sort of genealogical tree that will fit with our theories of classification, for, when all is said, the animal, in its widest generalization, is represented by a digestive tube. With this common factor, the way lies open to every kind of error. A machine is judged not by this or that train of wheels, but by the nature of the work accomplished. The monumental roasting-jack of a waggoners' inn and a Breguet chronometer both have trains of cogwheels geared in almost a similar fashion (4). Are we to class the two mechanisms together? Shall we forget that the one turns a shoulder of mutton before the hearth, while the other divides time into seconds?
In the same way, the organic scaffolding is dominated from on high by the aptitudes of the animal, especially that superior characteristic, the psychical aptitudes. That the Chimpanzee and the hideous Gorilla possess close resemblances of structure to our own is obvious. But let us for a moment consider their aptitudes. What differences, what a dividing gulf! Without exalting ourselves as high as the famous reed of which Pascal speaks, that reed which, in its weakness, by the mere fact that it knows itself to be crushed, is superior to the world that crushes it, we may at least ask to be shown, somewhere, an animal making an implement, which will multiply its skill and its strength, or taking possession of fire, the primordial element of progress (5). Master of implements and of fire! These two aptitudes, simple though they be, characterize man better than the number of his vertebrae and his molars.
You tell us that man, at first a hairy brute, walking on all fours, has risen on his hind-legs and shed his fur; and you complacently demonstrate how the elimination of the hairy pelt was effected. Instead of bolstering up a theory with a handful of fluff gained or lost, it would perhaps be better to settle how the original brute became the possessor of implements and fire. Aptitudes are more important than hair; and you neglect them because it is there that the insurmountable difficulty really resides. See how the great master of evolution hesitates and stammers when he tries, by fair means or foul, to fit instinct into the mould of his formulae. It is not so easy to handle as the colour of the pelt, the length of the tail, the ear that droops or stands erect. Yes, our master well knows that this is where the shoe pinches! Instinct escapes him and brings his theory crumbling to the ground.
Let us return to what the Scoliae teach us on this question, which incidentally touches on our own origin. In conformity with the Darwinian ideas, we have accepted an unknown precursor, who by dint of repeated experiment, adopted as the victuals to be hoarded the larvae of the Scarabaeidae. This precursor, modified by varying circumstances, is supposed to have subdivided herself into ramifications, one of which, digging into vegetable mould and preferring the Cetonia to any other game inhabiting the same heap, became the Two-banded Scolia; another, also addicted to exploring the soil, but selecting the Oryctes, left as its descendant the Garden Scolia; and a third, establishing itself in sandy ground, where it found the Anoxia, was the ancestress of the Interrupted Scolia. To these three ramifications we must beyond a doubt add others which complete the series of the Scolia. As their habits are known to me only by analogy, I confine myself to mentioning them.
The three species at least, therefore, with which I am familiar would appear to be derived from a common precursor. To traverse the distance from the starting-point to the goal, all three have had to contend with difficulties, which are extremely grave if considered one by one and are aggravated even more by this circumstance, that the overcoming of one would lead to nothing unless the others were surmounted as successfully. Success, then, is contingent upon a series of conditions, each one of which offers almost no chance of victory, so that the fulfilment of them all becomes a mathematical absurdity if we are to invoke accident alone.
And, in the first place, how was it that the Scolia of antiquity, having to provide rations for her carnivorous family, adopted for her prey only those larvae which, owing to the concentration of their nervous systems, form so remarkable and so rare an exception in the insect order? What chance would hazard offer her of obtaining this prey, the most suitable of all because the most vulnerable? The chance represented by unity compared with the indefinite number of entomological species. The odds are as one to immensity.
Let us continue. The larva of the Scarabaeid is snapped up underground, for the first time. The victim protests, defends itself after its fashion, coils itself up and presents to the sting on every side a surface on which a wound entails no serious danger. And yet the Wasp, an absolute novice, has to select, for the thrust of its poisoned weapon, one single point, narrowly restricted and hidden in the folds of the larva's body. If she miscalculates, she may be killed: the larva, irritated by the smarting puncture, is strong enough to disembowel her with the tusks of its mandibles. If she escapes the danger, she will nevertheless perish without leaving any offspring, since the necessary provisions will be lacking. Salvation for herself and her race depends on this: whether at the first thrust she is able to reach the little nervous plexus which measures barely one-fiftieth of an inch in width. What chance has she of plunging her lancet into it, if there is nothing to guide her? The chance represented by unity compared with the number of points composing the victim's body. The odds are as one against immensity.
Let us proceed still further. The sting has reached the mark; the fat grub is deprived of movement. At what spots should the egg now be laid? In front, behind, on the sides, the back or the belly? The choice is not a matter of indifference. The young grub will pierce the skin of its provender at the very spot on which the egg was fixed; and, once an opening is made, it will go ahead without hesitation. If this point of attack is ill-chosen, the nurseling runs the risk of presently finding under its mandibles some essential organ, which should have been respected until the end in order to keep the victuals fresh. Remember how difficult it is to complete the rearing when the tiny larva is moved from the place chosen by the mother. The game promptly becomes putrid and the Scolia dies.
It is impossible for me to state the precise motives which lead to the adoption of the spot on which the egg is laid; I can perceive general reasons, but the details escape me, as I am not well enough versed in the more delicate questions of anatomy and entomological physiology. What I do know with absolute certainty is that the same spot is invariably chosen for laying the egg. With not a single exception, on all the victims extracted from the heap of garden mould — and they are numerous — the egg is fixed behind the ventral surface, on the verge of the brown patch formed by the contents of the digestive system.
If there be nothing to guide her, what chance has the mother of gluing her egg to this point, which is always the same because it is that most favourable to successful rearing? A very small point, represented by the ratio of two or three square millimetres (6) to the entire surface of the victim's body.
Is this all? Not yet. The grub is hatched; it pierces the belly of the Cetonia-larva at the requisite point; it plunges its long neck into the entrails, ransacking them and filling itself to repletion. If it bite at random, if it have no other guide in the selection of tit-bits than the preference of the moment and the violence of an imperious appetite, it will infallibly incur the danger of being poisoned by putrid food, for the victim, if wounded in those organs which preserve a remnant of life in it, will die for good and all at the first mouthfuls.
The ample joint must be consumed with prudent skill: this part must be eaten before that and, after that, some other portion, always according to method, until the time approaches for the last bites. This marks the end of life for the Cetonia, but it also marks the end of the Scolia's feasting. If the grub be a novice in the art of eating, if no special instinct guide its mandibles in the belly of the prey, what chance has it of completing its perilous meal? As much as a starving Wolf would have of daintily dissecting his Sheep, when he tears at her gluttonously, rends her into shreds and gulps them down.
These four conditions of success, with chance so near to zero in each case, must all be realized together, or the grub will never be reared. The Scolia may have captured a larva with close-packed nerve-centres, a Cetonia-grub, for instance; but this will go for nothing unless she direct her sting towards the only vulnerable point. She may know the whole secret of the art of stabbing her victim, but this means nothing if she does not know where to fasten her egg. The suitable spot may be found, but all the foregoing will be useless if the grub be not versed in the method to be followed in devouring its prey while keeping it alive. It is all or nothing.
Who would venture to calculate the final chance on which the future of the Scolia, or of her precursor, is based, that complex chance whose factors are four infinitely improbable occurrences, one might almost say four impossibilities? And such a conjunction is supposed to be a fortuitous result, to which the present instinct is due! Come, come!
From another point of view again, the Darwinian theory is at variance with the Scoliae and their prey. In the heap of garden mould which I exploited in order to write this record, three kinds of larvae dwell together, belonging to the Scarabaeid group: the Cetonia, the Oryctes and Scarabeus pentodon. Their internal structure is very nearly similar; their food is the same, consisting of decomposing vegetable matter; their habits are identical: they live underground in tunnels which are frequently renewed; they make a rough egg-shaped cocoon of earthy materials. Environment, diet, industry and internal structure are all similar; and yet one of these three larvae, the Cetonia's, reveals a most singular dissimilarity from its fellow-trenchermen: alone among the Scarabaeidae and, more than that, alone in all the immense order of insects, it walks upon its back.
If the differences were a matter of a few petty structural details, falling within the finical department of the classifier, we might pass them over without hesitation; but a creature that turns itself upside down in order to walk with its belly in the air and never adopts any other method of locomotion, though it possesses legs and good legs at that, assuredly deserves examination. How did the animal acquire its fantastic mode of progress and why does it think fit to walk in a fashion the exact contrary of that adopted by other beasts?
To these questions the science now in fashion always has a reply ready: adaptation to environment. The Cetonia-larva lives in crumbling galleries which it bores in the depths of the soil. Like the sweep who obtains a purchase with his back, loins and knees to hoist himself up the narrow passage of a chimney, it gathers itself up, applies the tip of its belly to one wall of its gallery and its sturdy back to another; and the combined effort of these two levers results in moving it forward. The legs, which are used very little, indeed hardly at all, waste away and tend to disappear, as does any organ which is left unemployed; the back, on the other hand, the principal motive agent, grows stronger, is furrowed with powerful folds and bristles with grappling-hooks or hairs; and gradually, by adaptation to its environment, the creature loses the art of walking, which it does not practise, and replaces it by that of crawling on its back, a form of progress better suited to underground corridors.
So far so good. But now tell me, if you please, why the larvae of the Oryctes and the Scarabaeus, living in vegetable mould, the larva of the Anoxia, dwelling in the sand, and the larva of the Cockchafer in our cultivated fields have not also acquired the faculty of walking on their backs? In their galleries they follow the chimney-sweep's methods quite as cleverly as the Cetonia-grub; to move forward they make valiant use of their backs without yet having come to ambling with their bellies in the air. Can they have neglected to accommodate themselves to the demands of their environment? If evolution and environment cause the topsy-turvy progress of the one, I have the right, if words have any meaning whatever, to demand as much of the others, since their organization is so much alike and their mode of life identical.
I have but little respect for theories which, when confronted with two similar cases, are unable to interpret the one without contradicting the other. They make me laugh when they become merely childish. For example: why has the tiger a coat streaked black and yellow? A matter of environment, replies one of our evolutionary masters. Ambushed in bamboo thickets where the golden radiance of the sun is intersected by stripes of shadow cast by the foliage, the animal, the better to conceal itself, assumed the colour of its environment. The rays of the sun produced the tawny yellow of the coat; the stripes of shadow added the black bars.
And there you have it. Any one who refuses to accept the explanation must be very hard to please. I am one of these difficult persons. If it were a dinner-table jest, made over the walnuts and the wine, I would willingly sing ditto; but alas and alack, it is uttered without a smile, in a solemn and magisterial manner, as the last word in science! Toussenel, in his day, asked the naturalists an insidious question. Alphonse Toussenel (1803–1885), the author of a number of learned and curious works on ornithology (7). Why, he enquired, have Ducks a little curly feather on the rump? No one, so far as I know, had an answer for the teasing cross-examiner: evolution had not been invented then. In our time the reason why would be forthcoming in a moment, as lucid and as well-founded as the reason why of the tiger's coat.
Enough of childish nonsense. The Cetonia-grub walks on its back because it has always done so. The environment does not make the animal; it is the animal that is made for the environment. To this simple philosophy, which is quite antiquated nowadays, I will add another, which Socrates expressed in these words:
„What I know best is that I know nothing.“
1. Cf. „The Hunting Wasps“: chapters 1 to 3.
2. Known also as the Goatsucker, because of the mistaken belief that the bird sucks the milk of Goats, and, in America, as the Whippoorwill.
3. Felicien Cesar David (1810–1876). His chief work was the choral symphony „Le Desert“.
4. Louis Breguet (1803–1883), a famous Parisian watchmaker and physicist.
5. Blaise Pascal(1623–1662). The allusion is to a passage in the philosopher's „Pensees.“ Pascal describes man as a reed, the weakest thing in nature, but „a thinking reed.“
6. About 1/100 square inch.
7. Alphonse Toussenel (1803–1885), the author of a number of learned and curious works on ornithology.