THE GEOTRUPES: THE LARVA

The egg takes from one to two weeks to hatch, according as it is laid in October or September. As a rule the hatching takes place in the first fortnight of October. The larva grows pretty quickly and soon manifests very different characteristics from those displayed by the other Dung-beetles. We find ourselves in a new world, full of surprises. The grub is folded in two, it is bent into a hook, as required by the narrowness of the cell, which is scooped out gradually as the inside of the sausage is consumed.

Even so did the grubs of the Sacred Beetle, the Copris and the others comport themselves; but the larva of the Geotrupes has not the hump that gave the first-named such an ungainly figure. Its back is curved regularly. This entire absence of a knapsack, of a putty-bag, points to different habits. The larva, in fact, is not acquainted with the art of plugging crevices. If I contrive an opening in the part of the sausage which it occupies, I do not see it taking note of the hole, turning round and forthwith repairing the damage with a few pats of a trowel well supplied with cement. The access of the air does not trouble it apparently, or rather there is no provision against this in its means of defence.[222]

You have only to take a glance at its dwelling. What would be the use of the plasterer’s art of stopping up crannies, when the house simply cannot crack? Closely moulded in the cylinder of the burrow, the sausage is preserved from crumbling to dust by the support of its mould. The Sacred Beetle’s pear, which is free on every side in a large underground cavity, often swells, splits, peels off. The Geotrupes’ sausage, being packed in a casing, is free from these imperfections. Besides, if it were to burst, the accident would not be serious, for now, in autumn and winter, in a soil that is always damp and fresh, there is no fear of that desiccation which is so greatly dreaded by the pill-rollers. Hence there is no special industry designed to circumvent a peril that is unlikely and of little consequence; no excessively docile intestine to keep the trowel supplied; no ugly hump to act as a mortar-magazine. The inexhaustible evacuator of our earlier studies disappears and is replaced by a grub whose motions are more moderate.

Obviously, big eater as the larva is and, moreover, sequestered in a cell allowing of no communication with the outside, it is utterly ignorant of what we call cleanliness. Let us not take this to mean that it is disgustingly filthy, soiled with excrement: we should be making a grave mistake. Nothing could be neater or glossier than its satiny skin. We wonder what pains it must take over its toilet, or else what special grace enables all these eaters of ordure to keep themselves so clean. Seeing them outside their usual environment, no one would suspect their sordid life.

We must look elsewhere for any defect in cleanliness, if indeed it is right to give the name of defect to a quality which, all things considered, makes for the creature’s [223]good. Language, the one and only mirror of our thoughts, easily goes astray and becomes treacherous when attempting to express reality. Let us substitute the larva’s point of view for our own, let us throw off the man and become the Dung-beetle: offensive epithets will disappear forthwith.

The grub, that mighty eater, has no relations with the outside world. What is it to do with the remains of what it has digested? Far from being embarrassed by them, it takes advantage of them, as do many other solitaries cabined in a shell. It uses them to keep out the draughts from its hermitage and to pad it with quilting. It spreads them into a soft couch, grateful to its delicate skin; it builds them into a polished niche, a water-tight alcove which will protect the long winter torpor. I told you that one had but to imagine one’s self a Dung-beetle for a moment in order to change one’s language utterly. Behold that which was hateful and burdensome turned into something of value, which will contribute largely to the grub’s welfare. Onthophagi and Copres, Scarabæi and Gymnopleuri have accustomed us to this kind of industry.

The sausage is in an upright position, or nearly so. The hatching-chamber is at the bottom end. As the grub grows, it attacks the provisions overhead, but does not touch the wall around, which is of considerable thickness. It has indeed so huge a dish at its disposal that abstinence becomes no difficult matter. The Sacred Beetle’s grub, which has no occasion to take precautions against the winter, has a very skimpy helping. Its little pear is a niggardly ration and is consumed throughout, all but a slender wall, which the inmate, however, takes care to thicken and strengthen with a good layer of its mortar. The grub of the Geotrupes is very [224]differently situated. It is supplied with a colossal sausage, representing nearly a dozen times as much as the other provisions. However well endowed it be with stomach and appetite, it could not possibly consume the whole lot. Besides, the question of food is not the only one to be considered this time: there is also the serious matter of the hibernation. The parents foresaw the severity of the winter and bequeathed their sons the wherewithal to face it. The giant roly-poly will become a blanket against the cold.

The grub, as a matter of fact, gnaws bit by bit the part above and scoops out a corridor just wide enough to pass through. In this way, a very thick wall is left intact, the central part alone being consumed. As the sheath is bored, the sides are at the same time cemented and lined with the evacuations of the intestine. Any excess product accumulates and forms a rampart behind.

So long as the weather remains favourable, the grub moves about in its gallery; it takes its stand above or below and attacks the provisions with a tooth that grows daily more languid. Five or six weeks are thus passed in banqueting; then comes the cold weather, bringing the winter torpor with it. The grub now digs itself an oval recess, polished by much wriggling of its body, at the lower end of its case, in the mass of material which digestion has transformed into a fine paste; it protects itself with a curved canopy; and it is ready to enjoy its winter slumbers. It can sleep in peace. If its parents have installed it underground at an inconsiderable depth to which the frost penetrates, at any rate they have increased the supply of victuals to the utmost. The effect of this enormous superfluity is to provide an excellent dwelling for the bad weather.[225]

In December the grub is full-grown, or not far short of it. If the temperature only lent a hand, the nymphosis would now be due. But times are hard; and the grub, in its wisdom, decides to defer the delicate work of transformation. Sturdy creature that it is, it will be able to resist the cold much better than the nymph, that frail beginning of a new life. It therefore has patience and tarries in a state of torpor. I take it from its cell to examine it.

Convex on top and almost flat below, the larva is a semicylinder bent into a hook. There is an entire absence of the hump belonging to the previous Dung-beetles; likewise of any terminal trowel. The plasterer’s art of repairing crevices being unknown here, there is no need for the cement-pot or the spreading-utensil. The creature’s skin is smooth and white, clouded in the hinder half by the dark contents of the intestines. Sparse hairs, some fairly long, others very short, stand up on the median and dorsal region of the segments. They apparently serve to help the grub move about its cell by the mere wriggling of its hinder part. The head is neither big nor small and is pale-yellow in colour; the mandibles are large and brown at the tip.

But let us leave these details, which are of no great interest, and say at once that the creature’s prominent characteristic is supplied by its legs. The first two pairs are pretty long, especially for an animal leading a sedentary life in a narrow cabin. They are normally constructed; and it must be their strength that allows the grub to clamber about inside its pudding, converted into a sheath by eating. But the third pair presents a peculiarity of which I know no example elsewhere.[226]

The limbs forming this pair are rudimentary legs, crippled from birth, impotent, arrested in their development. They give one the impression of lifeless stumps. Their length is hardly a third of that of the others. More remarkable still, instead of pointing downwards like the normal legs, they shrivel upwards, turning towards the back, and remain indefinitely in that queer attitude, twisted and stiff. I cannot succeed in seeing the animal make the slightest use of them. Nevertheless they show the same joints as the others; but this is all on a greatly reduced scale, pale and inert. In short, a couple of words will distinguish the Geotrupes’ larva without any possibility of confusion: hind-legs atrophied.

This feature is so plain, so striking, so extraordinary that the least observant among us cannot mistake it. A grub crippled by nature and so evidently crippled enforces itself on our attention. What do the books say about it? Nothing, so far as I know. The few which I have with me are silent on this point. Mulsant, it is true, described the larva of the Stercoraceous Geotrupes; but he makes no mention of its exceptional structure. In his anxiety to describe the minutest details of the organism, has he lost sight of this monstrosity? Labrum, palpi, antennæ, the number of joints, the hairs: all this is set down and scrutinized; and the lifeless legs reduced to stumps are passed over in silence. Are the experts then so busy with the Gnat that they cannot see the Camel? I give it up.

Observe also that the hind-legs of the perfect insect are longer and stronger than the middle-legs and vie with the fore-legs in vigour. The atrophied limbs of the grub, therefore, become the adult’s powerful pressing-machine; [227]the impotent stumps change into strong stamping-tools.

Who will tell us the origin of these anomalies now thrice observed among the dung-workers? The Sacred Beetle, who is sound in every limb during his infancy, loses his fore-fingers when the adult form appears; the Onthophagus, who sports a horn on his thorax in his nymphal stage, drops it and does without the ornament in the end; the Geotrupes, at first a limping grub, turns his useless stumps into the best of his levers. The last-named makes progress; the others retrocede. Why does the cripple become able-bodied and why do the able-bodied become cripples?

We make chemical analyses of the suns; we surprise the nebulæ in labour and watch the birth of worlds; and shall we never know why a miserable grub is born limping? Come, ye divers who fathom life’s mysteries, descend a little lower into the depths and at least bring us back that humble pearl, the reply to the problems of the Geotrupes and the Sacred Beetle!

When the weather is severe, what becomes of the larva in the retreat which it has succeeded in making at the far end of its box? The exceptional cold of January and February 1895 will answer this question. My cages, always left in the open air, had repeatedly undergone a drop in temperature of some ten degrees below freezing-point. In this arctic weather, I conceived a wish to go in search of information and learn how things were progressing in my unprotected cages.

I could not manage it. The bed of earth, wetted by the earlier rains, had become a compact block throughout, which I should have had to break up like a stone with a hammer and chisel. Extraction by violent means was [228]not practicable: I should have endangered everything with my hammering. On the other hand, if any life remained in the frozen mass, I should have placed it in jeopardy by changing the temperature too suddenly. It was better to await the very slow natural thaw.

Early in March I inspect the cages again. This time there is no ice left. The earth is yielding and easy to dig. All the adult Geotrupes have died, bequeathing me a fresh supply of sausages, almost as plentiful as that which I had gathered and placed in safety in October. They have all perished; there is not a single survivor. Is cold or old age to blame?

At this very time and later, in April and May, when the new generation is wholly in the larval or at most in the nymphal stage, I often find adult Geotrupes busy in their scavenging-works. The old ones therefore see a second spring; they live long enough to know their children and to work with them, as do the Scarabæi, the Copres and others. These early ones are veterans. They have escaped the hardships of winter because they have been able to bury themselves far enough underground. Mine, kept captive between a few boards, have died for want of a sufficiently deep pit. At a time when they needed three feet of earth to shelter themselves, they had less than twelve inches. It was cold, therefore, that killed them, rather than age.

The low temperature, while fatal to the adult, has spared the larva. The few sausages left in position after my October diggings contain the grub in excellent condition. The protecting sheath has fulfilled its office to perfection: it has preserved the sons from the catastrophe that caused the death of the parents.[229]

The other cylinders, fashioned in the course of November, contain something even more remarkable. In their hatching-chamber, at the bottom, they hold an egg, all plump and shiny and as healthy-looking as though it had been laid that day. Can life still exist there? Is it possible, after the best part of the winter has been passed in a block of ice? I dare not believe it. The sausage itself has not an attractive appearance. It is darkened by fermentation, smells musty and does not suggest food worth having.

At all events, I will take the precaution of bottling the miserable puddings, after ascertaining that the egg is there in each case. I was well-advised. The fresh aspect of the germs, after wintering under such rude conditions, did not belie them. The hatching was soon effected; and early in May the late arrivals were almost as well-developed as their seniors, hatched in the autumn.

Some interesting facts are revealed by this piece of observation. First of all, the laying-period of the Geotrupes is a fairly long one, lasting from September to some time in November. At that date the first hoar-frosts begin; the soil is not warm enough to hatch the eggs; and the last ones, unable to hatch as swiftly as their predecessors, wait for the return of the fine weather. A few mild April days are enough to reawaken their suspended vitality. Then the usual evolution goes on, and this so rapidly that, notwithstanding a delay of five or six months, the backward larvæ are very nearly as big as the others by May, when the first nymphs appear.

Secondly, the Geotrupes’ eggs are capable of enduring the trials of severe cold unscathed. I do not know the exact temperature inside the frozen block which I tried to tackle with a mason’s chisel. Outside, the thermometer [230]sometimes fell to ten degrees below freezing-point; and, as the cold period lasted a long time, we may believe that the layer of earth in my boxes was equally cold. Now the Geotrupes’ puddings were enclosed in that frozen mass turned to a block of stone. A generous allowance must no doubt be made for the non-conductivity of these puddings composed of thready materials; the wall of dung did, to a certain extent, protect the larva and the egg against the biting cold, which, if experienced direct, would have been fatal. No matter: in that atmosphere the dung-cylinders, damp at the start, must in the long run have acquired the hardness of stone. In their hatching-chamber, in the tunnel made by the larva, the temperature undoubtedly sank below freezing-point.

Then what became of the grub and the egg? Were they really frozen? Everything seems to tell us so. That this most delicate of all delicate things, a germ, a rudiment of life in a blob of glair, should harden, turn into a bit of stone and then resume its vitality and continue its evolution after thawing seems inadmissible. And yet circumstances confirm it. We should have to credit the Geotrupes’ sausages with athermanous properties unequalled by any other substance to regard them as a sufficient protection against such intense and lasting refrigeration. What a pity that we could derive no information from the thermometer in this instance! After all, if complete freezing is unproven, one point has been established for certain: the egg and the grub of the Geotrupes can support and survive very low temperatures in their protecting sheath.

Since the occasion presents itself, let me say a few more words on the insect’s powers of resisting cold. [231]Some years ago, while looking for Scolia-cocoons in a heap of mould, I had made a large collection of the grubs of Cetonia aurata.1 I placed my loot in a flower-pot with a few handfuls of decayed vegetable matter, just enough to cover the insects’ backs. I intended to draw upon them for certain enquiries which I was making at the time. The pot remained in the open air; and I forgot all about it. A cold snap came, accompanied by sharp frost and snow. Then I remembered my Cetoniæ, so ill-protected against this kind of weather. I found the contents of the pot hardened into a conglomeration of earth, dead leaves, ice, snow and shrivelled grubs. It was a sort of almond-rock, in which the larvæ stood for the almonds. Sorely tried by the cold as they were, the colony ought to have perished. But no: when the thaw arrived, the frozen larvæ came to life again and began to swarm about as though nothing unusual had happened.

The insect’s powers of endurance are less great than the larva’s. As the organization becomes more refined, it loses its robustness. My cages, which went through such a bad time in the winter of 1895, provided me with a striking instance. A few species—Scarabæi, Copres, Pilularii and Onthophagi—were represented at the same time by newcomers and old stagers. All the Geotrupes, without an exception, died in the earthy bed which had turned into a block of stone; the Minotaurs also succumbed, every one of them. And yet both find their way up north and are not afraid of cold climates. On the other hand, the southern species, the Sacred Beetle, the Spanish Copris and Pilularius flagellatus, the younger [232]generation as well as the veterans, withstood the winter better than I dared hope. Many of them died, it is true; they formed the majority; but at any rate there were survivors whom I marvelled to see recovering from their icy paralysis, trotting about under the first kisses of the sun. In April, those specimens which have escaped from freezing resume their labours. They teach me that, when at liberty, Copres and Scarabæi have no need to retire to winter quarters at great depths underground. A moderate screen of earth, in some sheltered nook, is enough for them. Less skilful diggers than the Geotrupes, they are better provided with the power to resist a passing spell of cold.

We will end this digression by remarking, as so many others have done, that agriculture cannot reckon on the cold weather to rid it of its dread enemy, the insect. Very hard frosts, lasting a long time and penetrating well beneath the surface of the soil, can destroy various species which are not able to go down low enough; but a great many survive. Moreover, the grub and especially the egg in many cases defy our severest winters.

The first five days of April put an end to the torpor of the larvæ of both Geotrupes, snuggling on the bottom floor of their cylinder, in a temporary cell. Activity returns, bringing with it a last flicker of appetite. The remains of the autumn banquet are plentiful. The grub makes use of them no longer for greedy feasting, but just as a midnight snack between two slumbers, that of winter and the deeper sleep of the metamorphosis. Hence the sides of the sheath are attacked spasmodically. Breaches yawn, sections of wall come tumbling down, and soon the edifice is nothing but an unrecognizable ruin.[233]

The lower portion of the original sausage remains, however, with its walls intact for a length of an inch or two. Here, in a thick layer, the grub’s excreta are accumulated, held in reserve for the final work. In the centre of this mass a hollow is dug, carefully polished inside. With the excavated rubbish the grub builds not just a canopy, like that with which the winter alcove was protected, but a solid lid, with a rough outer surface, in appearance not unlike the work of the Cetoniæ when they wrap themselves in a shell of mould. This lid, with what is left of the pudding, forms a habitation which would remind us pretty closely of the Cockchafer’s dwelling, were it not truncated in the upper part, which moreover is most often topped by a few remnants from the destroyed cylinder.

The grub is now shut in for the transformation, motionless, with its body emptied of all dross. In a few days a blister appears on the dorsal surface of the last abdominal segments. This swells, spreads and gradually extends as far as the thorax. It is the work of excoriation beginning. Distended by a colourless liquid, the blister gives an uncertain glimpse of a sort of milky cloud, the first blurred outline of the new organism.

The thorax splits in front, the cast skin is slowly pushed backwards, and at last we have the nymph, all white, half-opaque and half-crystalline. I obtain my first nymphs about the beginning of May.

Four or five weeks later, the perfect insect arrives, white on the wing-cases and belly, while the rest of the body already possesses the normal colouring. The chromatic evolution is quickly completed; and, before the end of June, the Geotrupes, now perfectly matured, emerges from the soil at twilight and flies off to start on [234]his scavenger’s job without delay. The laggards, those whose egg has gone through the winter, are still in the white nymphal stage when their elders effect their release. Not before September is nigh will they burst their natal shell and, in their turn, sally forth to aid in the cleansing of the fields.