Chapter VII. Change of Diet
Jean-Henri Fabre More Hunting Wasp
Wasp with a captured spider
Brillat-Savarin, when pronouncing his famous maxim, „Tell me what you eat and I will tell you what you are,“ certainly never suspected the signal confirmation which the entomological world would bestow upon his saying. Our gastrosopher was speaking only of the culinary caprices of man rendered fastidious by the sweets of life; but he might, in a more serious department of thought, have given his formula a wider and more general bearing and applied it to the dishes which vary so greatly according to latitude, climate and customs; he might above all have taken into his reckoning the harsh realities suffered by the common people, when perhaps his ideal of moral worth would have been found in a platter of chick-peas oftener than in a pot of pate de foie gras. No matter: his aphorism, the mere whimsical sally of an epicure, becomes an imperious truth if we forget the luxury of the table and look into what is eaten by the little world which swarms around us.
To each its mess. The cabbage Pieris consumes the pungent leaves of the Cruciferae as the food of her infancy; the Silkworm disdains any foliage other than that of the mulberry-tree. The Spurge Hawk-moth requires the caustic milk-sap of the tithymals: the Corn-weevil the grain of wheat; the Pea-weevil, the seeds of the Leguminosae; the Balaninus (1) the hazel-nut, the chestnut, the acorn; the Brachycera (2) the clove of garlic. Each has its diet, each its plant; and each plant has its customary guests. Their relations are so precise that in many cases one might determine the insect by the vegetable which supports it, or the vegetable by the insect.
If you know the lily, you may name as a Crioceris the tiny scarlet Scarabaeid that inhabits it and peoples its leaves with larvae which keep themselves cool beneath an overcoat of ordure (3). If you know the Crioceris, you may name as a lily the plant which she devastates. It will not perhaps be the common or white lily, but some other representative of the same family — Turk's cap lily, orange lily, scarlet Martagon, lancifoliate lily, tiger-spotted lily, golden lily — hailing from the Alps or the Pyrenees, or brought from China or Japan. Relying on the Crioceris, who is an expert judge of exotic as well as of native Liliaceae, you may name as a lily the plant with which you are unacquainted and trust the word of this singular botanical master. Whether the flower be red, yellow, ruddy-brown or sown with crimson spots, characteristics so unlike the immaculate whiteness of the familiar flower, do not hesitate, adopt the name dictated by the Beetle. Where man is liable to mistake the insect is never mistaken.
This insect botany, a cause of such grievous tribulations, has always impressed the worker in the fields, who for all that, is a very indifferent observer. The man who was the first to see his cabbage-plot devastated by caterpillars made the acquaintance of the Pieris. Science completed the process, in its desire to serve a useful purpose or merely to seek truth for truth's sake; and to-day the relations between the insect and the plant form a collection of records as important from the philosophical as from the practical, agricultural point of view. What is much less familiar to us, because it touches us less nearly, is the zoology of the insect, that is to say, the selection which it makes, to feed its larva, of this or that animal species, to the exclusion of others. The subject is so vast that a volume were not sufficient to exhaust it; besides, data are lacking in the vast majority of cases. It is reserved for a still very distant future to raise this point of biology to the level already reached by the question of vegetable diet. It will be enough if I contribute a few observations scattered through my writings or my notes.
What does the Wasp addicted to a predatory life eat, of course in the larval state? Now, to begin with, we see natural sections which adopt as their prey different species of one and the same order, in one and the same group. Thus the Ammophilae hunt exclusively the larvae of the night-flying Moths. This taste is shared by the Eumenes, a very different genus (4). The Spheges and Tachytes are addicted to Orthoptera; the Cerceres, apart from a few exceptions, are faithful to the Weevil; both the Philanthi and the Palari capture only Hymenoptera; the Pompili specialize in hunting the Spider; the Astata revels in the flavour of Bugs; the Bembeces want Flies and nothing else; the Scoliae enjoy the monopoly of the Lamellicorn-grubs; the Pelopaei favour the young Epeirae (5), the Stizi vary in opinion: of the two in my neighbourhood, one, S. ruficornis, fills her larder with Mantes and the other, S. tridentatus, fills it with Cicadellae (6); lastly, the Crabronidae (7). levy tribute upon the rabble of the Muscidae (8).
Already you see what a magnificent classification of these game-hunters might be made with a faithfully listed bill of fare. Natural groups stand out, characterized merely by the identity of their victuals. I trust that the methodical science of the future will take account of these gastronomic laws, to the great relief of the entomological novice, who is too often hampered by the snares of the mouth-parts, the antennae and the nervures of the wings. I call for a classification in which the insect's aptitudes, its diet, its industry and its habits shall take precedence of the shape of a joint in its antennae. It will come; but when?
If from generalities we descend to details, we shall see that the very species may, in many instances, be determined from the nature of its victuals. The number of burrows of Philanthus apivorus which I have inspected since I have been rummaging the hot roadside embankments, to enquire into their population, would seem hyperbolical were I able to state the figures (9). They must amount, it seems to me, to thousands. Well, in this multitude of food-stores, whether recent or ancient, uncovered for a purpose or encountered by chance, I have not once, not as often as once, discovered other remains than those of the Hive-bee: the imperishable wings, still connected in pairs, the cranium and thorax enveloped in a violet shroud, the winding-sheet which time throws over these relics. To-day as when I was a beginner, ever so long ago; in the north as in the south of the country which I explored; in mountainous regions as on the plains, the Philanthus follows an unvarying diet: she must have the Hive-bee, always the Bee and never any other, however closely various other kinds of game resemble the Bee in quality. If, therefore, when exploring sunny banks, you find beneath the soil a small parcel of mutilated Bees, that will be enough to point to the existence of a local colony of Philanthus apivorus. She alone knows the recipe for making potted Bee-meat. The Crioceris was but now teaching us all about the lily family; and here the mildewed body of the Bee tells us of the Philanthus and her lair.
Similarly the female Ephippiger helps us to identify the Languedocian Sphex: her relics, the cymbals and the long sabre, are the unmistakable sign of the cocoon to which they adhere. The black Cricket, with his red-braided thighs, is the infallible label of the Yellow-winged Sphex; the larva of Oryctes nasicornis tells us of the Garden Scolia as certainly as the best description; the Cetonia-grub proclaims the Two-banded Scolia and the larva of the Anoxia announces the Interrupted Scolia.
After these exclusive ones, who disdain to vary their meals, let us mention the eclectics, who, in a group which is generally well-defined, are able to select among different kinds of game appropriate to their bulk. The Great Cerceris (10) favours above all Cleonus ophthalmicus, one of the largest of our Weevils; but at need she accepts the other Cleoni, as well as the kindred genera, provided that the capture be of an imposing size. Cerceris arenaria (11) extends her hunting-grounds farther afield: any Weevil of average dimensions is to her a welcome capture. The Buprestis-hunting Cerceris adopts all the Buprestes indiscriminately, so long as they are not beyond her strength. The Crowned Philanthus (P. coronatus, FAB.) fills her underground warehouses with Halicti chosen among the biggest (12). Much smaller than her kinswoman, Philanthus raptor, LEP., stores away Halicti chosen among the less large species. Any adult Acridian approaching an inch in length suits the White-banded Sphex. The various tidae of the neighbourhood are admitted to the larder of Stizus ruficornis and of the Mantis-hunting Tachytes on the sole condition of being young and tender. The largest of our Bembeces (B. rostrata, FAB., and B. bidentata, VAN DER LIND (13)) are eager consumers of Gad-flies. With these chief dishes they associate relishes levied indifferently from the rest of the Fly clan. The Sandy Ammophila (A. sabulosa, VAN DER LIND (14)) and the Hairy Ammophila (A. hirsuta, KIRB.) cram into each burrow a single but corpulent caterpillar, always of the Moth tribe and varying greatly in coloration, which denotes distinct species. The Silky Ammophila (15)) has a better assorted diet. She requires for each banqueter three or four items, which include the Measuring-worms, or Loopers, and the caterpillars of ordinary Moths, all of which are equally appreciated. The Brown-winged Solenius (S. fascipennis, LEP.), who elects to dwell in the soft dead wood of old willow-trees, has a marked preference for Virgil's Bee, Eristalis tenax (16), willingly adding, sometimes as a side-dish, sometimes as the principal game, Helophilus pendulus, whose costume is very different. On the faith of indistinguishable remains, we must no doubt enter a number of other Flies in her game-book. The Golden-mouthed Hornet (Crabro chrysostomus, LEP.) another burrower in old willow-trees, prefers the Syrphi, without distinction of species (17). The Wandering Solenius (18)), an inmate of the dry bramble-stems and of the dwarf-elder, lays under contribution for her larder the genera Syritta, Sphaerophoria, Sarcophaga, Syrphus, Melanophora, Paragus and apparently many others. The species which recurs most frequently in my notes is Syritta pipiens.
Without pursuing this tedious list any farther, we plainly perceive the general result. Each huntress has her characteristic tastes, so much so that, when we know the bill of fare, we can tell the genus and very often the species of the guest, thus proving the proud truth of the maxim, „Tell me what you eat and I will tell you what you are.“
There are some which always need the same prey. The offspring of the Languedocian Sphex religiously consume the Ephippiger, that family dish so dear to their ancestors and no less dear to their descendants; no innovation in the ancient usages can tempt them. Others are better suited by variety, for reasons connected with flavour or with facility of supply; but then the selection of the game is kept within fixed limits. A natural group, a genus, a family, more rarely almost a whole order: this is the hunting-ground beyond which poaching is strictly forbidden. The law is absolute; and one and all scrupulously refrain from transgressing it.
In the place of the Praying Mantis, offer the Mantis-hunting Tachytes an equivalent in the shape of a Locust. She will scorn the morsel, though it would seem to be of excellent flavour, seeing that Panzer's Tachytes prefers it to any other form of game. Offer her a young Empusa, who differs so widely from the Mantis in shape and colour: she will accept without hesitation and operate before your eyes. Despite its fantastic appearance, the Devilkin is instantly recognized by the Tachytes as a Mantid and therefore as game falling within her scope.
In exchange for her Cleonus, give to the Great Cerceris a Buprestis, the delight of one of her near kinsfolk. She will have nothing to say to the sumptuous dish. Accept that! She, a Weevil-eater! Never in this world! Present her with a Cleonus of a different species, or any other large Weevil, of a sort which she has most probably never seen before, since it does not figure on the inventory of the provisions in her burrows. This time there is no show of disdain: the victim is seized and stabbed in the regulation manner and forthwith stored away.
Try to persuade the Hairy Ammophila that Spiders have a nutty flavour, as Lalande asserts; and you will see how coldly your hints are received (19). Try merely to convince her that the caterpillar of a Butterfly is as good to eat as the caterpillar of a Moth. You will not succeed. But, if you substitute for her underground larva, which I suppose to be grey, another underground larva striped with black, yellow, rusty-red or any other tint, this change of coloration will not prevent her from recognizing, in the substituted dish, a victim to her liking, an equivalent of her Grey Worm.
So with the rest, so far as I have been able to experiment with them. Each obstinately refuses what is alien to her hunting-preserves, each accepts whatever belongs to them, always provided that the game substituted is much the same in size and development as that whereof the owner has been deprived. Thus the Tarsal Tachytes, an appreciative epicure of tender flesh, would not consent to replace her pinch of young Acridian-grubs with the one big Locust that forms the food of Panzer's Tachytes; and the latter, in her turn, would never exchange her adult Acridian for the other's menu of small fry. The genus and the species are the same, but the age differs; and this is enough to decide the question of acceptance or refusal.
When its depredations cover a somewhat extensive group, how does the insect manage to recognize the genera, the species composing her allotted portion and to distinguish them from the rest with an assured vision which the inventory of her burrows proves never to be at fault? Is it the general appearance that guides her? No, for in some Bembex-burrows we shall find Sphaerophoriae, those slender, thong-like creatures, and Bombylii, looking like velvet pincushions; no again, for in the pits of the Silky Ammophila we shall see, side by side, the caterpillar of the ordinary shape and the Measuring-worm, a living pair of compasses which progresses by alternately opening out and closing; no, once more, for in the storerooms of Stizus ruficornis and the Mantis-hunting Tachytes we see stacked beside the Mantis the Empusa, her unrecognizable caricature.
Is it the colouring? Not at all. There is no lack of instances. What a variety of hues and metallic reflections, distributed in a host of different fashions, appear in the Buprestes that are hunted by the Cerceris celebrated by L?on Dufour (20). A painter's palette, containing crushed gold, bronze, ruby and amethyst, would find it difficult to rival these sumptuous colours. Nevertheless the Cerceris makes no mistake: all this nation of insects, so indifferently attired, represents to her, as to the entomologist, the nation of the Buprestes. The inventory of the Hornet's larder will include Diptera clad in grey or russet frieze; others are girdled with yellow, flecked with white, adorned with crimson lines; others are steel-blue, ebony black, or coppery green; and underneath this variety of dissimilar costumes we find the invariable Fly.
Let us take a concrete example. Ferrero's Cerceris (C. Ferreri, VAN DER LIND) consumes Weevils. Her burrows are usually lined with Phynotomi and Sitones both an indeterminate grey, and Otiorhynchi, black or tan-coloured. Now I have sometimes happened to unearth from her cells a collection of veritable jewels which, thanks to their bright metallic lustre, made a most striking contrast with the sombre Otiorhynchus. These were the Rhynchites (R. betuleti), who roll the vine-leaves into cigars. Equally magnificent, some of them were azure blue, others copper gilt, for the cigar-roller has a twofold colouring. How did the Cerceris manage to recognize in these jewels the Weevil, the near relative of the vulgar Phynotomus? Any such encounters probably found her lacking in expert knowledge; her race cannot have handed down to her other than very indeterminate propensities, for she does not appear to make frequent use of the Rhynchites, as is proved by my infrequent discovery of them amid the mass of my numerous excavations. For the first time, perhaps, passing through a vineyard, she saw the rich Beetle gleaming on a leaf; it was not for her a dish in current consumption, consecrated by the ancient usages of the family. It was something novel, exceptional, extraordinary. Well, this extraordinary creature is recognized with certainty as a Weevil and stored away as such. The glittering cuirass of the Rhynchites goes to take its place beside the grey cloak of the Phynotomus. No, it is not the colour that guides the choice.
Neither is it the shape. Cerceris arenaria hunts any medium-sized Weevil. I should be putting the reader's patience to too great a test if I attempted to give in this place a complete inventory of the specimens identified in her larder. I will mention only two, which my latest searches around my village have revealed. The Wasp goes hunting on the holm-oaks of the neighbouring hills the Pubescent Brachyderes (B. pubescens) and the Acorn-weevil (Balaninus glandium). What have these two Beetles in common as regards shape? I mean by shape not the structural details which the classifier examines through his magnifying-glass, not the delicate features which a Latreille would quote when drawing up a technical description, but the general picture, the general outline that impresses itself upon the vision even of an untrained eye and makes the man who knows nothing of science and above all the child, a most perspicacious observer, connect certain animals together.
In this respect, what have the Brachyderes and the Balaninus in common in the eyes of the townsman, the peasant, the child or the Cerceris? Absolutely nothing. The first has an almost cylindrical figure; the second, squat, short and thickset, is conical in front and elliptical, or rather shaped like the ace of hearts, behind. The first is black, strewn with cloudy, mouse-grey spots; the second is yellow ochre. The head of the first ends in a sort of snout; the head of the second tapers into a curved beak, slender as a horse-hair and as long as the rest of the body. The Brachyderes has a massive proboscis, cut off short; the Balaninus seems to be smoking an insanely long cigarette-holder.
Who would think of connecting two creatures so unlike, of calling them by the same name? Outside the professional classifiers, no one would dare to. The Cerceris, more perspicacious, knows each of them for a Weevil, a quarry with a concentrated nervous system, lending itself to the surgical feat of her single stroke of the lancet. After obtaining an abundant booty at the cost of the blunt-mouthed insect, with which she sometimes stuffs her cellars to the exclusion of any other fare, according to the hazards of the chase, she now suddenly sees before her the creature with the extravagant proboscis. Accustomed to the first, will she fail to know the second? By no means: at the first glance she recognizes it as her own; and the cell already furnished with a few Brachyderes receives its complement of Balanini. If these two species are to seek, if the burrows are far from the holm-oaks, the Cerceris will attack Weevils displaying the greatest variety of genus, species, form and coloration, levying tribute indifferently on Sitones, Cneorhini, Geonemi, Otiorhynchi, Strophosomi and many others.
In vain do I rack my brains merely to guess at the signs upon which the huntress relies as a guide, without going outside one and the same group, in the midst of such a variety of game; above all by what characteristics she recognizes as a Weevil the strange Acorn Balaninus, the only one among her victims that wears a long pipe-stem. I leave to evolutionism, atavism and other transcendental „isms“ the honour and also the risk of explaining what I humbly recognize as being too far beyond my grasp. Because the son of the bird-catcher who imitates the call of his victims has been fed on roast Robins, Linnets and Chaffinches, shall we hastily conclude that this education through the stomach will enable him later, without other initiation than that of the spit, to know his way about the ornithological groups and to avoid confusing them when his turn comes to set his limed twigs? Will the digesting of a ragout of little birds, however often repeated by him or his ascendants, suffice to make him a finished bird-catcher? The Cerceris has eaten Weevil; her ancestors have all eaten Weevil, religiously. If you see in this the reason that makes the Wasp a Weevil-expert endowed with a perspicacity unrivalled save by that of a professional entomologist, why should you refuse to admit that the same consequences would follow in the bird-catcher's family?
I hasten to abandon these insoluble problems in order to attack the question of provisions from another point of view. Every Hunting Wasp is confined to a certain genus of game, which is usually strictly limited. She pursues her appointed quarry and regards anything outside it with suspicion and distaste. The tricks of the experimenter, who drags her prey from under her and flings her another in exchange, the emotions of the possessor deprived of her property and immediately recovering it, but under another form, are powerless to put her on the wrong scent. Obstinately she refuses whatever is alien to her portion; instantly she accepts whatever forms part of it. Whence arises this insuperable repugnance for provisions to which the family is unaccustomed? Here we may appeal to experiment. Let us do so: its dictum is the only one that can be trusted.
The first idea that presents itself and the only one, I think, that can present itself is that the larva, the carnivorous nurseling, has its preferences, or we had better say its exclusive tastes. This kind of game suits it; that does not; and the mother provides it with food in conformity with its appetites, which are unchangeable in each species. Here the family dish is the Gad-fly; elsewhere it is the Weevil; elsewhere again it is the Cricket, the Locust and the Praying Mantis. Good in themselves, in a general way, these several victuals may be noxious to a consumer who is not used to them. The larva which dotes on Locust may find caterpillar a detestable fare; and that which revels in caterpillar may hold Locust in horror. It would be hard for us to discover in what manner Cricket-flesh and Ephippiger-flesh differ as juicy, nourishing foodstuffs; but it does not follow that the two Sphex-wasps addicted to this diet have not very decided opinions on the matter, or that each of them is not filled with the highest esteem for its traditional dish and a profound dislike for the other. There is no discussing tastes.
Moreover, the question of health may well be involved. There is nothing to tell us that the Spider, that treat for the Pompilus, is not poison, or at least unwholesome food, to the Bembex, the lover of Gad-flies; that the Ammophila's succulent caterpillar is not repugnant to the stomach of the Sphex fed upon the dry Acridian. The mother's esteem for one kind of game and her distrust of another would in that case be due to the likes and dislikes of her larvae; the victualler would regulate the bill of fare by the gastronomic demands of the victualled.
This exclusiveness of the carnivorous larva seems all the more probable inasmuch as the larva reared on vegetable food refuses in any way to lend itself to a change of diet. However pressed by hunger, the caterpillar of the Spurge Hawk-moth, which browses on the tithymals, will allow itself to starve in front of a cabbage leaf which makes a peerless meal for the Pieris. Its stomach, burned by pungent spices, will find the Crucifera insipid and uneatable, though its piquancy is enhanced by essence of sulphur. The Pieris, on its part, takes good care not to touch the tithymals: they would endanger its life. The caterpillar of the Death's-head Hawk-moth requires the solanaceous narcotics, principally the potato, and will have nothing else. All that is not seasoned with solanin it abhors. And it is not only larvae whose food is strongly spiced with alkaloids and other poisonous substances that refuse any innovation in their food; the others, even those whose diet is least juicy, are invincibly uncompromising. Each has its plant or its group of plants, beyond which nothing is acceptable.
I remember a late frost which had nipped the buds of the mulberry-trees during the night, just when the first leaves were out. Next day there was great excitement among my neighbours: the Silk-worms had hatched and the food had suddenly failed. The farmers had to wait for the sun to repair the disaster; but how were they to keep the famishing new-born grubs alive for a few days? They knew me for an expert in plants; by collecting them as I walked through the fields I had earned the name of a medical herbalist. With poppy-flowers I prepared an elixir which cleared the sight; with borage I obtained a syrup which was a sovran remedy for whooping-cough; I distilled camomile; I extracted the essential oil from the wintergreen. In short, botany had won for me the reputation of a quack doctor. After all, that was something.
The housewives came in search of me from every point of the compass and with tears in their eyes explained the situation. What could they give their Silk-worms while waiting for the mulberry to sprout afresh? It was a serious matter, well worthy of commiseration. One was counting on her batch to buy a length of cloth for her daughter, who was on the point of getting married; another told me of her plans for a Pig to be fattened against the coming winter; all deplored the handful of crown-pieces which, hoarded in the hiding-place in the cupboard, would have afforded help in difficult times. And, full of their troubles, they unfolded, before my eyes, a scrap of flannel on which the vermin were swarming:
„Regardas, moussu! Venoun d'espeli; et ren per lour douna! Ah, pecaire!“ „Look, sir! The frost has come and we've nothing to give them! Oh, what a misfortune!“
Poor people! What a harsh trade is yours: respectable above all others, but of all the most uncertain! You work yourselves to death; and, when you have almost reached your goal, a few hours of a cold night, which comes upon you suddenly, destroys your harvest. To help these afflicted ones seemed to me a very difficult thing. I tried, however, taking botany as my guide; it suggested to me, as substitutes for the mulberry, the members of closely-related families: the elm, the nettle-tree, the nettle, the pellitory. Their nascent leaves, chopped small, were offered to the Silk-worms. Other and far less logical attempts were made, in accordance with the inspiration of the individuals. Nothing came of them. To the last specimen, the new-born Silk-worms died of hunger. My renown as a quack must have suffered somewhat from this check. Was it really my fault? No, it was the fault of the Silk-worm, which remained faithful to its mulberry leaf.
It was therefore in nearly the certainty of non-fulfilment that I made my first attempts at rearing carnivorous larvae with a quarry which did not conform with the customary regimen. For conscience' sake, more or less perfunctorily, I endeavoured to achieve something that seemed to me bound to end in pitiful failure. Only the Bembex-wasps, which are plentiful in the sand of the neighbouring hills, might still afford me, without too prolonged a search, a few subjects on which to experiment. The Tarsal Bembex furnished me with what I wanted: larvae young enough to have still before them a long period of feeding and yet sufficiently developed to endure the trials of a removal.
These larva are exhumed with all the consideration which their delicate skin demands; a number of head of game are likewise unearthed intact, having been recently brought by the mother. They consist of various Diptera, including some Anthrax-flies (21). An old sardine-box, containing a layer of sifted sand and divided into compartments by paper partitions, receives my charges, who are isolated one from another. These Fly-eaters I propose to turn into Grasshopper-eaters; for their Bembex-diet I intend to substitute the diet of a Sphex or a Tachytes. To save myself tedious errands devoted to provisioning the refectory, I accept what good fortune offers me at the very threshold of my door. A green Locustid, with a short sabre bent into a reaping-hook, Phaneroptera falcata, is ravaging the corollae of my petunias. Now is the time to indemnify myself for the damage which she has caused me. I pick her young, half to three-quarters of an inch in length; and I deprive her of movement, without more ado, by crushing her head. In this condition she is served up to the Bembex-larvae in place of their Flies.
If the reader has shared my convictions of failure, convictions based on very logical motives, he will now share my profound surprise. The impossible becomes possible, the senseless becomes reasonable and the expected becomes the opposite of the real. The dish served on the Bembeces' table for the first time since Bembeces came into the world is accepted without any repugnance and consumed with every mark of satisfaction. I will here set down the detailed diary of one of my guests; that of the others would only be a repetition, save for a few variations.
2 AUGUST, 1883. — The larva of the Bembex, as I extract it from its burrow, is about half-developed. Around it I find only some scanty relics of its meals, consisting chiefly of Anthrax-wings, half-diaphanous and half-clouded. The mother would appear to have completed the victualling by fresh contributions, added day by day. I give the nurseling, which is an Anthrax-eater, a young Phaneroptera. The Locustid is attacked without hesitation. This profound change in the character of its victuals does not seem in the least to disturb the larva, which bites straight into the rich morsel with its mandibles and does not let go until it has exhausted it. Towards evening the drained carcase is replaced by another, quite fresh, of the same species but bulkier, measuring over three-quarters of an inch.
3 AUGUST. — Next day I find the Phaneroptera devoured. Nothing remains but the dry integuments, which are not dismembered. The entire contents have disappeared; the game has been emptied through a large opening made in the belly. A regular Grasshopper-eater could not have operated more skilfully. I replace the worthless carcase by two small Locustidae. At first the larva does not touch them, being amply sated with the copious meal of the day before. In the afternoon, however, one of the items is resolutely attacked.
4 AUGUST. — I renew the victuals, although those of the day before are not finished. For the rest, I do the same daily, so that my charge may constantly have fresh food at hand. High game might upset its stomach. My Locustidae are not victims at the same time living and inert, operated upon according to the delicate method of the insects that paralyse their prey; they are corpses, procured by a brutal crushing of the head. With the temperature now prevailing, flesh soon becomes tainted; and this compels me frequently to renew the provisions in my sardine-box refectory. Two specimens are served up. One is attacked soon afterwards; and the larva clings to it assiduously.
5 AUGUST. — The ravenous appetite of the start is becoming assuaged. My supplies may well be too generous; and it might be prudent to try a little dieting after this Gargantuan good cheer. The mother certainly is more parsimonious. If all the family were to eat at the same rate as my guest, she would never be able to keep pace with their demands. Therefore, for reasons of health, this is a day of fasting and vigil.
6 AUGUST. — Supplies are renewed with two Phaneropterae. One is consumed entirely; the other is bitten into.
7 August. — To-day's ration is tasted and then abandoned. The larva seems uneasy. With its pointed mouth it explores the walls of its chamber. This sign denotes the approach of the time for making the cocoon.
8 AUGUST. — During the night the larva has spun its silken eel-trap. It is now encrusting it with grains of sand. Then follow, in due time, the normal phases of the metamorphosis. Fed on Locustidae, a diet unknown to its race, the larva passes through its several stages without any more difficulty than its brothers and sisters fed on Flies.
I obtained the same success in offering young Mantes for food. One of the larvae thus served would even incline me to believe that it preferred the new dish to the traditional diet of its race. Two Eristales, or Drone-flies, and a Praying Mantis an inch long composed its daily allowance. The Drone-flies are disdained from the first mouthful; and the Mantis, already tasted and apparently found excellent, causes the Fly to be completely forgotten. Is this an epicure's preference, due to the greater juiciness of the flesh? I am not in a position to say. At all events, the Bembex is not so infatuated with Fly as to refuse to abandon it for other game.
The failure which I foresaw has proved a magnificent success. It is fairly convincing, is it not? Without the evidence of experiment, what can we rely upon? Beneath the ruins of so many theories which appeared to be most solidly erected I should hesitate to admit that two and two make four if the facts were not before me. My argument had the most tempting probability on its side, but it had not the truth. As it is always possible to find reasons after the event in support of an opinion which one would not at first admit, I should now argue as follows:
The plant is the great factory in which are elaborated, with mineral materials, the organic principles which are the materials of life. Certain products are common to the whole vegetable series, but others, far less numerous, are prepared in special laboratories. Each genus, each species has its trade-mark. Here essential oils are manufactured; here alkaloids; here starches, fatty substances, resins, sugars, acids. Hence result special energies, which do not suit every herbivorous animal. It assuredly requires a stomach made expressly for the purpose to digest aconite, colchicum, hemlock or henbane; those who have not such a stomach could never endure a diet of that sort. Besides, the Mithridates fed on poison resist only a single toxin (22). The caterpillar of the Death's-head Hawk-moth, which delights in the solanin of the potato, would be killed by the acrid principle of the tithymals that form the food of the Spurge-caterpillar. The herbivorous larvae are therefore perforce exclusive in their tastes, because different genera of vegetables possess very different properties.
With this variety in the products of the plant, the animal, a consumer far more than a producer, contrasts the uniformity in its own products. The albumen in the egg of the Ostrich or the Chaffinch, the casein in the milk of the Cow or the Ass, the muscular flesh of the Wolf or the Sheep, the Screech-owl or the Field-mouse, the Frog or the Earth-worm: these remain albumen, casein or fibrin, edible if not eaten. Here are no excruciating condiments, no special acridities, no alkaloids fatal to any stomach other than that of the appointed consumer; so that animal food is not confined to one and the same eater. What does not man eat, from that delicacy of the arctic regions, soup made of Seal's blood and a scrap of Whale-blubber wrapped in a willow-leaf for a vegetable, to the Chinaman's fried Silk-worm or the Arab's dried Locust? What would he not eat, if he had not to overcome the repugnance dictated by habit rather than by actual necessity? The prey being uniform in its nutritive principles, the carnivorous larva ought to accommodate itself to any sort of game, above all if the new dish be not too great a departure from consecrated usage. Thus should I argue, with no less probability on my side, had I to begin all over again. But, as all our arguments have not the value of a single fact, I should be forced in the end to resort to experiment.
I did so the next year, on a larger scale and with a greater variety of subjects. I shrink from a continuous narrative of my experiments and of my personal education in this new art, where the failure of one day taught me the way to succeed on the morrow. It would be long and tedious. Enough if I briefly state my results and the conditions which must be fulfilled in order to run the delicate refectory as it should be run.
And, first, we must not dream of detaching the egg from its natural prey to lay it on another. The egg adheres pretty firmly, by its cephalic pole, to the quarry. To remove it from its place would inevitably jeopardize its future. I therefore let the larva hatch and acquire sufficient strength to bear the removal without peril. For that matter, my excavations most often provide me with my subjects in the form of larvae. I adopt for rearing-purposes the larvae that are a quarter to a half developed. The others are too young and risky to handle, or too old and limited to a short period of artificial feeding.
Secondly, I avoid bulky heads of game, a single one of which would suffice for the whole growing-stage. I have already said and I here repeat how nice a matter it is to consume a victim which has to keep fresh for a couple of weeks and not to finish dying until it is almost entirely devoured. Death here leaves no corpse; when life is extinct, the body has disappeared, leaving only a shred of skin. Larvae with only one large prey have a special art of eating, a dangerous art, in which a clumsy bite would prove fatal. If bitten before the proper time at such a point, the victim becomes putrid, which promptly causes death by poisoning in the consumer. When diverted from its plan of attack, deprived of its clue, the larva is not always able to rediscover the lawful morsels in good time and is killed by the decomposition of its badly dissected prey. What will happen if the experimenter gives it a game to which it is not accustomed? Not knowing how to eat it according to rule, the larva will kill it; and by next day the victuals will have become so much toxic putrescence. I have already told how I found it impossible to rear the Two-banded Scolia on Oryctes-larvae, fastened down to deprive them of movement, or even on Ephippigers, paralysed by the Languedocian Sphex. In both cases the new diet was accepted without hesitation, a proof that it suited the nurseling; but in a day or two putrescence supervened and the Scolia perished on the fetid morsel. The method of preserving the Ephippiger, so well known to the Sphex, was unknown to my boarder; in this was enough to convert a delicious food into poison.
Even so did my other attempts miscarry wretchedly, attempts at feeding with the single dish consisting of one big head of game to replace the normal ration. Only one success is recorded in my notebooks, but that was so difficult that I would not undertake to obtain it a second time. I succeeded in feeding the larva of the Hairy Ammophila with an adult black Cricket, who was accepted as readily as the natural game, the caterpillar.
To avoid putrefaction of victuals which last overlong and are not consumed according to the method indispensable to their preservation, I employ small game, each piece of which can be finished by the larva at a single sitting, or at most in a single day. It matters little then that the victim is slashed and dismembered at random; decomposition has no time to seize upon its still quivering tissues. This is the procedure of those larvae which gulp down their food, snapping at random without distinguishing one part from another, such as the Bembex-larvae, which finish the Fly into which they have bitten before beginning another in the heap, or the Cerceris-larvae, which drain their Weevils methodically one after another. With the first strokes of the mandibles the victim broached may be mortally wounded. This is no disadvantage: a brief spell suffices to make use of the corpse, which is saved from putrefaction by being promptly consumed. Close beside it, the other victims, quite alive though motionless, await their respective turns and supply reserves of victuals which are always fresh.
I am too unskilful a butcher to imitate the Wasp and myself to resort to paralysis; moreover, the caustic liquid injected into the nerve-centres, ammonia in particular, would leave traces of smell or flavour which might put off my boarders. I am therefore compelled to deprive my insects of the power of movement by killing them outright. This makes it impracticable to provide a sufficiency of provisions beforehand in a single supply: while one item of the ration was being consumed the rest would spoil. One expedient alone remains to me, one which entails constant attendance: it is to renew the provisions each day. When all these conditions are fulfilled, the success of artificial feeding is still not without its difficulties; nevertheless, with a little care and above all plenty of patience, it is almost certain.
Wasp eating a praying mantis
It was thus that I reared the Tarsal Bembex, which eats Anthrax-flies and other Diptera, on young Locustidae or Mantidae; the Silky Ammophila, whose diet consists chiefly of Measuring-worms, on small Spiders; the pot-making Pelopaeus, a Spider-eater, on tender Acridians; the Sand Cerceris, a passionate lover of Weevils, on Halicti; the Bee-eating Philanthus, which feeds exclusively on Hive-bees, on Eristales and other Flies. Without succeeding in my final aim, for reasons which I have just explained, I have seen the Two-banded Scolia feasting greedily on the grub of the Oryctes, which was substituted for that of the Cetonia, and putting up with an Ephippiger taken from the burrow of the Sphex; I have been present at the repast of three Hairy Ammophilae accepting with an excellent appetite the Cricket that replaced their caterpillar. One of them, as I have related, contrived to keep its ration fresh, which enabled it to reach its full development and to spin its cocoon.
These examples, the only ones to which my experiments have extended hitherto, seem to me sufficiently convincing to allow me to conclude that the carnivorous larva does not have exclusive tastes. The ration supplied to it by the mother, so monotonous, so limited in quality, might be replaced by others equally to its taste. Variety does not displease the larva; it does it as much good as uniformity; indeed, it would be of greater benefit to the race, as we shall see presently.
1. A genus of Beetles including the Acorn-weevil, the Nut-weevil and others.
2. A division of Flies including the Gad-flies and Robber-flies.
3. For the Lily-beetle, or Crioceris merdigera, cf. „The Glow-worm and Other Beetles,“ by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chapters 16 and 17. Back
4. Cf. „The Mason-wasps“ by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chapter 1.
5. Or Garden Spiders. Cf. „The Life of the Spider“: chapters 9 to 14 and appendix.
6. Cf. „The Life of the Grasshopper“: chapter 20.
7. Any Flies akin to the House-fly.
9. For the Bee-eating Philanthus cf. Chapter 10 of the present volume.
10. Cerceris tuberculata. Cf. „The Hunting Wasps“: chapters 2 and 3.
11. Cf. idem: chapter 1.
12. Cf. „Bramble-bees and Others“ by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chapters 12 to 14.
13. For the Rostrate Bembex and the Two-pronged Bembex, cf. „The Hunting Wasps“: chapter 14.
14. Cf. idem: chapter 13.
15. A. holosericea, VAN DER LIND. (Cf. idem: chapter 14.)
16. Actually the Common Drone-fly and somewhat resembling a Bee in appearance. Cf. „The Hunting Wasps“: chapter 14.
17. The Syrphi, like the Eristales, resemble Bees through having the abdomen transversely banded with yellow.
18. S. vagus, LEP. (For this Fly-hunting insect cf. „Bramble-bees and Others“: chapters 1 and 3.
19. Joseph Jerome Le Francois de Lalande (1732–1807), the astronomer. Even after he had achieved his reputation, he sought means, outside the domain of science, to make himself talked about and found these in the display partly of odd tastes, such as that for eating Spiders and caterpillars, and partly of atheistical opinions.
20. Jean Marie L?on Dufour (1780–1865) was an army surgeon who served with distinction in several campaigns and subsequently practised as a doctor in the Landes. He attained great eminence as a naturalist. Cf. „The Hunting Wasps“: chapter 1; also „The Life of the Spider“: chapter 1.
21. Cf. „The Life of the Fly“: chapters 2 and 4.
22. Mithridates VI. King of Pontus (d. B.C. 63) is said to have secured immunity from poison by taking increased doses of it.