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!