Chapter II. The Scoliae
Jean-Henri Fabre More Hunting Wasp
Hairy Flower Wasp (Scolia Soror)
Were strength to take precedence over the other zoological attributes, the Scoliae would hold a predominant place in the front rank of the Wasps. Some of them may be compared in size with the little bird from the north, the Golden-crested Wren, who comes to us at the time of the first autumn mists and visits the rotten buds. The largest and most imposing of our sting-bearers, the Carpenter-bee, the Bumble-bee, the Hornet, cut a poor figure beside certain of the Scoliae. Of this group of giants my district possesses the Garden Scolia (S. hortorum, VAN DER LIND), who is over an inch and a half in length and measures four inches from tip to tip of her outspread wings, and the Hemorrhoidal Scolia (S. haemorrhoidalis, VAN DER LIND), who rivals the Garden Scolia in point of size and is distinguished more particularly by the bundle of red hairs bristling at the tip of the abdomen.
A black livery, with broad yellow patches; leathery wings, amber-coloured, like the skin of an onion, and watered with purple reflections; thick, knotted legs, covered with sharp hairs; a massive frame; a powerful head, encased in a hard cranium; a stiff, clumsy gait; a low, short, silent flight: this gives you a concise description of the female, who is strongly equipped for her arduous task. The male, being a mere philanderer, sports a more elegant pair of horns, is more daintily clad and has a more graceful figure, without altogether losing the quality of robustness which is his consort's leading characteristic.
It is not without a certain alarm that the insect-collector finds himself for the first time confronted by the Garden Scolia. How is he to capture the imposing creature, how to avoid its sting? If its effect is in proportion to the Wasp's size, the sting of the Scolia must be something terrible. The Hornet, though she unsheath her weapon but once, causes the most exquisite pain. What would it be like if one were stabbed by this colossus? The prospect of a swelling as big as a man's fist and as painful as the touch of a red-hot iron passes through our mind at the moment when we are bringing down the net. And we refrain, we beat a retreat, we are greatly relieved not to have aroused the dangerous creature's attention.
Yes, I confess to having run away from my first Scoliae, anxious though I was to enrich my budding collection with this magnificent insect. There were painful recollections of the Common Wasp and the Hornet connected with this excess of prudence. I say excess, for to-day, instructed by long experience, I have quite recovered from my former fears; and, when I see a Scolia resting on a thistle-head, I do not scruple to take her in my fingers, without any precaution whatever, however large she may be and however menacing her aspect. My courage is not all that it seems to be; I am quite ready to tell the Wasp-hunting novice this. The Scoliae are notably peaceable. Their sting is an implement of labour far more than a weapon of war; they use it to paralyse the prey destined for their offspring; and only in the last extremity do they employ it in self-defence. Moreover, the lack of agility in their movements nearly always enables us to avoid their sting; and, even if we be stung, the pain is almost insignificant. This absence of any acute smarting as a result of the poison is almost constant in the Hunting Wasps, whose weapon is a surgical lancet and devised for the most delicate physiological operations.
Among the other Scoliae of my district I will mention the Two-banded Scolia (S. bifasciata, VAN DER LIND), whom I see every year, in September, working at the heaps of leaf-mould which are placed for her benefit in a corner of my paddock; and the Interrupted Scolia (S. interrupta, LATR.), the inhabitant of the sandy soil at the foot of the neighbouring hills. Much smaller than the two preceding insects, but also much commoner, a necessary condition of continuous observation, they will provide me with the principal data for this study of the Scoliae.
I open my old note book; and I see myself once more, on the 6th of August, 1857, in the Bois des Issards, that famous copse near Avignon which I have celebrated in my essay on the Bembex-wasps (1). Once again, my head crammed with entomological projects, I am at the beginning of my holidays which, for two months, will allow me to indulge in the insect's company.
A fig for Mariotte's flask and Toricelli's tube! (2) (3). This is the thrice-blest period when I cease to be a schoolmaster and become a schoolboy, the schoolboy in love with animals. Like a madder-cutter off for his day's work, I set out carrying over my shoulder a solid digging-implement, the local luchet, and on my back my game-bag with boxes, bottles, trowel, glass tubes, tweezers, lenses and other impedimenta. A large umbrella saves me from sunstroke. It is the most scorching hour of the hottest day in the year. Exhausted by the heat, the Cicadae are silent. The bronze-eyed Gad-flies seek a refuge from the pitiless sun under the roof of my silken shelter; other large Flies, the sobre-hued Pangoniae, dash themselves recklessly against my face.
The spot at which I have installed myself is a sandy clearing which I had recognized the year before as a site beloved of the Scoliae. Here and there are scattered thickets of holm-oak, whose dense undergrowth shelters a bed of dead leaves and a thin layer of mould. My memory has served me well. Here, sure enough, as the heat grows a little less, appear, coming I know not from whence, some Two-banded Scoliae. The number increases; and it is not long before I see very nearly a dozen of them about me, close enough for observation. By their smaller size and more buoyant flight, they are easily known for males. Almost grazing the ground, they fly softly, going to and fro, passing and repassing in every direction. From time to time one of them alights on the ground, feels the sand with his antennae and seems to be enquiring into what is happening in the depths of the soil; then he resumes his flight, alternately coming and going.
What are they waiting for? What are they seeking in these evolutions of theirs, which are repeated a hundred times over? Food? No, for close beside them stand several eryngo-stems, whose sturdy clusters are the Wasps' usual resource at this season of parched vegetation; and not one of them settles upon the flowers, not one of them seems to care about their sugary exudations. Their attention is engrossed elsewhere. It is the ground, it is the stretch of sand which they are so assiduously exploring; what they are waiting for is the arrival of some female, who bursting the cocoon, may appear from one moment to the next, issuing all dusty from the ground. She will not be given time to brush herself or to wash her eyes: three or four more of them will be there at once, eager to dispute her possession. I am too familiar with the amorous contests of the Hymenopteron clan to allow myself to be mistaken. It is the rule for the males, who are the earlier of the two, to keep a close guard around the natal spot and watch for the emergence of the females, whom they pester with their pursuit the moment they reach the light of day. This is the motive of the interminable ballet of my Scoliae. Let us have patience: perhaps we shall witness the nuptials.
The hours go by; the Pangoniae and the Gad-flies desert my umbrella; the Scoliae grow weary and gradually disappear. It is finished. I shall see nothing more to-day. I repeat my laborious expedition to the Bois des Issards over and over again; and each time I see the males as assiduous as ever in skimming over the ground. My perseverance deserved to succeed. It did, though the success was very incomplete. Let me describe it, such as it was; the future will fill up the gaps.
A female issues from the soil before my eyes. She flies away, followed by several males. With the luchet I dig at the point of emergence; and, as the excavation progresses, I sift between my fingers the rubbish of sand mixed with mould. In the sweat of my brow, as I may justly say, I must have removed nearly a cubic yard of material, when at last I make a find. This is a recently ruptured cocoon, to the side of which adheres an empty skin, the last remnant of the game on which the larva fed that wrought the said cocoon. Considering the good condition of its silken fabric, this cocoon may have belonged to the Scolia who has just quitted her underground dwelling before my eyes. As for the skin accompanying it, this has been so much spoilt by the moisture of the soil and by the grassy roots that I cannot determine its origin exactly. The cranium, however, which is better-preserved, the mandibles and certain details of the general configuration lead me to suspect the larva of a Lamellicorn.
It is getting late. This is enough for to-day. I am worn out, but amply repaid for my exertions by a broken cocoon and the puzzling skin of a wretched grub. Young people who make a hobby of natural history, would you like to discover whether the sacred fire flows in your veins? Imagine yourselves returning from such an expedition. You are carrying on your shoulder the peasant's heavy spade; your loins are stiff with the laborious digging which you have just finished in a crouching position; the heat of an August afternoon has set your brain simmering; your eyelids are tired by the itch of an inflammation resulting from the overpowering light in which you have been working; you have a devouring thirst; and before you lies the dusty prospect of the miles that divide you from your well-earned rest. Yet something stings within you; forgetful of your present woes you are absolutely glad of your excursion. Why? Because you have in your possession a shred of rotten skin. If this is so, my young friends, you may go ahead, for you will do something, though I warn you that this does not mean, by a long way, that you will get on in the world.
I examined this shred of skin with all the care that it deserved. My first suspicions were confirmed: a Lamellicorn, a Scarabaeid in the larval state, is the first food of the Wasp whose cocoon I have just unearthed. But which of the Scarabaeidae? And does this cocoon, my precious booty, really belong to the Scoliae? The problem is beginning to take shape. To attempt its solution we must go back to the Bois des Issards.
I did go back and so often that my patience ended by being exhausted before the problem of the Scoliae had received a satisfactory solution. The difficulties are great indeed, under the conditions. Where am I to dig in the indefinite stretch of sandy soil to light upon a spot frequented by the Scoliae? The luchet is driven into the ground at random; and almost invariably I find none of what I am seeking. To be sure, the males, flying level with the ground, give me a hint, at the outset, with their certainty of instinct, as to the spots where the females ought to be; but their hints are very vague, because they go so far in every direction. If I wished to examine the soil which a single male explores in his flight, with its constantly changing course, I should have to turn over, to the depth of perhaps a yard, at least four poles of earth. This is too much for my strength and the time at my disposal. Then, as the season advances, the males disappear, whereupon I am suddenly deprived of their hints. To know more or less where I should thrust my luchet, I have only one resource left, which is to watch for the females emerging from the ground or else entering it. With a great expenditure of time and patience I have at last had this windfall, very rarely, I admit.
The Scoliae do not dig a burrow which can be compared with that of the other Hunting Wasps; they have no fixed residence, with an unimpeded gallery opening on the outer world and giving access to the cells, the abodes of the larvae. They have no entrance- and exit-doors, no corridor built in advance. If they have to make their way underground, any point not hitherto turned over serves their purpose, provided that it be not too hard for their digging-tools, which, for that matter, are very powerful; if they have to come out, the point of exit is no less indifferent. The Scolia does not bore the soil through which she passes: she excavates and ploughs it with her legs and forehead; and the stuff shifted remains where it lies, behind her, forthwith blocking the passage which she has followed. When she is about to emerge into the outer world, her advent is heralded by the fresh soil which heaps itself into a mound as though heaved up by the snout of some tiny Mole. The insect sallies forth; and the mound collapses, completely filling up the exit-hole. If the Wasp is entering the ground, the digging-operations, undertaken at an arbitrary point, quickly yield a cavity in which the Scolia disappears, separated from the surface by the whole track of shifted material.
I can easily trace her passage through the thickness of the soil by certain long, winding cylinders, formed of loose materials in the midst of compact and stable earth. These cylinders are numerous; they sometimes run to a depth of twenty inches; they extend in all directions, fairly often crossing one another. Not one of them ever exhibits so much as a suspicion of an open gallery. They are obviously not permanent ways of communication with the outer world, but hunting-trails which the insect has followed once, without going back to them. What was the Wasp seeking when she riddled the soil with these tunnels which are now full of running sands? No doubt the food for her family, the larva of which I possess the empty skin, now an unrecognizable shred.
I begin to see a little light: the Scoliae are underground workers. I already expected as much, having before now captured Scoliae soiled with little earthy encrustations on the joints of the legs. The Wasp, who is so careful to keep clean, taking advantage of the least leisure to brush and polish herself, could never display such blemishes unless she were a devoted earth-worker. I used to suspect their trade, now I know it. They live underground, where they burrow in search of Lamellicorn-grubs, just as the Mole burrows in search of the White Worm (4). It is even possible that, after receiving the embraces of the males, they but very rarely return to the surface, absorbed as they are by their maternal duties; and this, no doubt, is why my patience becomes exhausted in watching for their entrance and their emergence.
It is in the subsoil that they establish themselves and travel to and fro; with the help of their powerful mandibles, their hard cranium, their strong, prickly legs, they easily make themselves paths in the loose earth. They are living ploughshares. By the end of August, therefore, the female population is for the most part underground, busily occupied in egg-laying and provisioning. Everything seems to tell me that I should watch in vain for the appearance of a few females in the broad daylight; I must resign myself to excavating at random.
The result was hardly commensurate with the labour which I expended on digging. I found a few cocoons, nearly all broken, like the one which I already possessed, and, like it, bearing on their side the tattered skin of a larva of the same Scarabaeid. Two of these cocoons which are still intact contained a dead adult Wasp. This was actually the Two-banded Scolia, a precious discovery which changed my suspicions into a certainty.
I also unearthed some cocoons, slightly different in appearance, containing an adult inmate, likewise dead, in whom I recognized the Interrupted Scolia. The remnants of the provisions again consisted of the empty skin of a larva, also a Lamellicorn, but not the same as the one hunted by the first Scolia. And this was all. Now here, now there, I shifted a few cubic yards of soil, without managing to find fresh provisions with the egg or the young larva. And yet it was the right season, the egg-laying season, for the males, numerous at the outset, had grown rarer day by day until they disappeared entirely. My lack of success was due to the uncertainty of my excavations, in which I had nothing to guide me over the indefinite area covered.
If I could at least identify the Scarabaeidae whose larvae form the prey of the two Scoliae, the problem would be half solved. Let us try. I collect all that the luchet has turned up: larvae, nymphs and adult Beetles. My booty comprises two species of Lamellicorns: Anoxia villosa and Euchlora Julii, both of whom I find in the perfect state, usually dead, but sometimes alive. I obtain a few of their nymphs, a great piece of luck, for the larval skin which accompanies them will serve me as a standard of comparison. I come upon plenty of larvae, of all ages. When I compare them with the cast garment abandoned by the nymphs, I recognize some as belonging to the Anoxia and the rest to the Euchlora.
With these data, I perceive with absolute certainty that the empty skin adhering to the cocoon of the Interrupted Scolia belongs to the Anoxia. As for the Euchlora, she is not involved in the problem: the larva hunted by the Two-banded Scolia does not belong to her any more than it belongs to the Anoxia. Then with which Scarabaeid does the empty skin which is still unknown to me correspond? The Lamellicorn whom I am seeking must exist in the ground which I have been exploring, because the Two-banded Scolia has established herself there. Later — oh, very long afterwards! — I recognized where my search was at fault. In order not to find a network of roots beneath my luchet and to render the work of excavation lighter, I was digging the bare places, at some distance from the thickets of holm-oak; and it was just in those thickets, which are rich in vegetable mould, that I should have sought. There, near the old stumps, in the soil consisting of dead leaves and rotting wood, I should certainly have come upon the larva so greatly desired, as will be proved by what I have still to say.
Here ends what my earlier investigations taught me. There is reason to believe that the Bois des Issards would never have furnished me with the precise data, in the form in which I wanted them. The remoteness of the spot, the fatigue of the expeditions, which the heat rendered intensely exhausting, the impossibility of knowing which points to attack would undoubtedly have discouraged me before the problem had advanced a step farther. Studies such as these call for home leisure and application, for residence in a country village. You are then familiar with every spot in your own grounds and the surrounding country and you can go to work with certainty.
Twenty-three years have passed; and here I am at S?rignan, where I have become a peasant, working by turns on my writing-pad and my cabbage-patch. On the 14th of August, 1880, Favier (5) clears away a heap of mould consisting of vegetable refuse and of leaves stacked in a corner against the wall of the paddock. This clearance is considered necessary because Bull, when the lovers' moon arrives, uses this hillock to climb to the top of the wall and thence to repair to the canine wedding the news of which is brought to him by the effluvia borne upon the air. His pilgrimage fulfilled, he returns, with a discomfited look and a slit ear, but always ready, once he has had his feed, to repeat the escapade. To put an end to this licentious behaviour, which has cost him so many gaping wounds, we decided to remove the heap of soil which serves him as a ladder of escape.
Favier calls me while in the midst of his labours with the spade and barrow:
„Here's a find, sir, a great find! Come and look.“
I hasten to the spot. The find is a magnificent one indeed and of a nature to fill me with delight, awakening all my old recollections of the Bois des Issards. Any number of females of the Two-banded Scolia, disturbed at their work, are emerging here and there from the depth of the soil. The cocoons also are plentiful, each lying next to the skin of the victim on which the larva has fed. They are all open but still fresh: they date from the present generation; the Scoliae whom I unearth have quitted them not long since. I learnt later, in fact, that the hatching took place in the course of July.
In the same heap of mould is a swarming colony of Scarabaeidae in the form of larvae, nymphs and adult insects. It includes the largest of our Beetles, the common Rhinoceros Beetle, or Oryctes nasicornis. I find some who have been recently liberated, whose wing-cases, of a glossy brown, now see the sunlight for the first time; I find others enclosed in their earthen shell, almost as big as a Turkey's egg. More frequent is her powerful larva, with its heavy paunch, bent into a hook. I note the presence of a second bearer of the nasal horn, Oryctes Silenus, who is much smaller than her kinswoman, and of Pentodon punctatus, a Scarabaeid who ravages my lettuces.
But the predominant population consists of Cetoniae, or Rosechafers, most of them enclosed in their egg-shaped shells, with earthen walls encrusted with dung. There are three different species: C. aurata, C. morio and C. floricola. Most of them belong to the first species. Their larvae, which are easily recognized by their singular talent for walking on their backs with their legs in the air, are numbered by the hundred. Every age is represented, from the new born grub to the podgy larva on the point of building its shell.
This time the problem of the victuals is solved. When I compare the larval slough sticking to the Scolia's cocoons with the Cetonia-larvae or, better, with the skin cast by these larvae, under cover of the cocoon, at the moment of the nymphal transformation, I establish an absolute identity. The Two-banded Scolia rations each of her eggs with a Cetonia-grub. Behold the riddle which my irksome searches in the Bois des Issards had not enabled me to solve. To-day, at my threshold, the difficult problem becomes child's play. I can investigate the question easily to the fullest possible extent; I need not put myself out at all; at any hour of the day, at any period that seems favourable, I have the requisite elements before my eyes. Ah, dear village, so poor, so countrified, how happily inspired was I when I came to ask of you a hermit's retreat, where I could live in the company of my beloved insects and, in so doing, set down not too unworthily a few chapters of their wonderful history!
According to the Italian observer Passerini, the Garden Scolia feeds her family on the larvae of Oryctes nasicornis, in the heaps of old tan-waste removed from the hot-houses. I do not despair of seeing this colossal Wasp coming to establish herself one day in my heaps of leaf-mould, in which the same Scarabaeid is swarming. Her rarity in my part of the country is probably the only cause that has hitherto prevented the realization of my wishes.
I have just shown that the Two-banded Scolia feeds in infancy on Cetonia-larvae and particularly on those of C. aurata, C. morio and C. floricola. These three species dwell together in the rubbish-heap just explored; their larvae differ so little that I should have to examine them minutely to distinguish the one from the other; and even then I should not be certain of succeeding. It seems probable that the Scolia does not choose between them, that she uses all three indiscriminately. Perhaps she even assails other larvae, inhabitants, like the foregoing, of heaps of rotting vegetable-matter. I therefore set down the Cetonia genus generally as forming the prey of the Two-banded Scolia.
Lastly, round about Avignon, the Interrupted Scolia used to prey upon the larva of the Shaggy Anoxia (A. villosa). At Serignan, which is surrounded by the same kind of sandy soil, without other vegetation than a few sparse seed-bearing grasses, I find her rationing her young with the Morning Anoxia (A. matutinalis). Oryctes, Cetoniae and Anoxiae in the larval state: here then is the prey of the three Scoliae whose habits we know. The three Beetles are Lamellicorns, Scarabaeidae. We shall have occasion later to consider the reason of this very striking coincidence.
For the moment, the business in hand is to move the heap of leaf-mould to some other place, with the wheelbarrow. This is Favier's work, while I myself collect the disturbed population in glass jars, in order to put them back into the new rubbish-heap with all the consideration which my plans owe to them. The laying-time has not yet set in, for I find no eggs, no young Scolia-larvae. September apparently will be the propitious month. But there are bound to be many injured in the course of this upheaval; some of the Scoliae have flown away who will perhaps have a certain difficulty in finding the new site; I have disarranged everything in the overturned heap. To allow tranquility to be restored and habit to resume its rounds, to give the population time to increase and replace the fugitives and the injured, it would be best, I think, to leave the heap alone this year and not to resume my investigations until the next. After the thorough confusion due to the removal, I should jeopardize success by being too precipitate. Let us wait one year more. I decide accordingly, curb my impatience and resign myself. We will simply confine ourselves to enlarging the heap, when the leaves begin to fall, by accumulating the refuse that strews the paddock, so that we may have a richer field of operations.
In the following August, my visits to the mound of leaf-mould become a daily habit. By two o'clock in the afternoon, when the sun has cleared the adjacent pine-trees and is shining on the heap, numbers of male Scoliae arrive from the neighbouring fields, where they have been slaking their thirst on the eryngo-heads. Incessantly coming and going with an indolent flight, they circle round the heap. If some female rise from the soil, those who have seen her dart forward. A not very turbulent affray decides which of the suitors shall be the possessor; and the couple fly away over the wall. This is a repetition of what I used to see in the Bois des Issards. By the time that August is over. The males have ceased to show themselves. The mothers do not appear either: they are busy underground, establishing their families.
On the 2nd of September, I decide upon a search with my son Emile, who handles the fork and the shovel, while I examine the clods dug up. Victory! A magnificent result, finer than any that my fondest ambition would have dared to contemplate! Here is a vast array of Cetonia-larvae, all flaccid, motionless, lying on their backs, with a Scolia's egg sticking to the centre of their abdomen; here are young Scolia-larvae dipping their heads into the entrails of their victims; here are others farther advanced, munching their last mouthfuls of a prey which is drained dry and reduced to a skin; here are some laying the foundation of their cocoons with a reddish silk, which looks as if it had been dyed in Bullock's blood; here are some whose cocoons are finished. There is plenty of everything, from the egg to the larva whose period of activity is over. I mark the 2nd of September as a red-letter day; it has given me the final key to a riddle which has kept me in suspense for nearly half a century.
I place my spoils religiously in shallow, wide-mouthed glass jars containing a layer of finely sifted mould. In this soft bed, which is identical in character with the natal surroundings, I make some faint impressions with my fingers, so many cavities, each of which receives one of my subjects, one only. A pane of glass covers the mouth of the receptacle. In this way I prevent a too rapid evaporation and keep my nurselings under my eyes without fear of disturbing them. Now that all this is in order, let us proceed to record events.
The Cetonia-larvae which I find with a Scolia's egg upon their ventral surface are distributed in the mould at random, without special cavities, without any sign of some sort of structure. They are smothered in the mould, just as are the larvae which have not been injured by the Wasp. As my excavations in the Bois des Issards told me, the Scolia does not prepare a lodging for her family; she knows nothing of the art of cell-building. Her offspring occupies a fortuitous abode, on which the mother expends no architectural pains. Whereas the other Hunting Wasps prepare a dwelling to which the provisions are carried, sometimes from a distance, the Scolia confines herself to digging her bed of leaf-mould until she comes upon a Cetonia-larva. When she finds a quarry, she stabs it on the spot, in order to immobilize it; and, again on the spot, she lays an egg on the ventral surface of the paralysed creature. That is all. The mother goes in quest of another prey without troubling further about the egg which has just been laid. There is no effort of carting or building. At the very spot where the Cetonia-grub is caught and paralysed, the Scolia-larva hatches, grows and weaves its cocoon. The establishment of the family is thus reduced to the simplest possible expression.
1. Cf. „The Hunting Wasps“: chapter 14.
2. Edme Mariotte (1620–1684), a French chemist who discovered, independently of Robert Boyle the Irishman (1627–1691), the law generally known as Boyle's law, which states that the product of the volume and the temperature of a gas is constant at constant temperature. His flask is an apparatus contrived to illustrate atmospheric pressure and ensure a constant flow of liquid.
3. Evangelista Toricelli (1608–1647), a disciple of Galileo and professor of philosophy and mathematics at Florence. His „tube“ is our mercury barometer. He was the first to obtain a vacuum by means of mercury; and he also improved the microscope and the telescope.
4. The larva of the Cockchafer. This grub takes three years or more to arrive at maturity underground.
5. An ex-soldier who acted as the author's gardener and factotum.