The Glow-Worm and Other Beetles Part 12

This excursion to the pampas leans to one conclusion of some importance. We find in another hemisphere, with reversed seasons, a different climate and dissimilar biological conditions, a series of true dung-workers whose habits and industry repeat, in their essential facts, the habits and industry of our own. Prolonged investigations, made at first hand and not, like mine, at second hand, would add greatly to the list of similar workers.

And it is not only in the gra.s.sy plains of La Plata that the modellers of dung proceed according to the principles usual over here; we may say, without fear of being mistaken, that the magnificent Copres of Ethiopia and the big Sacred Beetles of Senegambia work exactly like our own.

The same similarity of industry exists in other entomological series, however distant their country. My books give details of a Pelopaeus[19]

in Sumatra, who is an ardent Spider-huntress like our own, who builds mud cells inside houses and who, like her, is fond of the loose hangings of the window-curtains for the s.h.i.+fting foundation of her nests. They tell me of a Scolia[20] in Madagascar who serves each of her grubs with a fat rasher, an Oryctes-larva,[21] even as our own Scoliae feed their family on prey of similar organization, with a highly concentrated nervous system, such as the larvae of Cetoniae, Anoxiae and even Oryctes. They tell me that in Texas a Pepsis, a huntress of big game akin to the Calicurgi, gives chase to a formidable Tarantula and vies in daring with our Ringed Calicurgus,[22] who stabs the Black-bellied Lycosa.[23] They tell me that the Sphex-wasps of the Sahara, a rival of our own White-banded Sphex,[24] operate on Locusts. But we must limit these quotations, which could easily be multiplied.

[Footnote 19: Cf. _The Mason-wasps_, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chaps. iii. to vi.--_Translator's Note_.]

[Footnote 20: The chapters on the Scoliae will appear in _More Hunting Wasps_. Meanwhile, cf. _The Life and Love of the Insect_, by J. Henri Fabre, translated by Alexander Teixeira de Mattos: chap.

xi.--_Translator's Note_.]

[Footnote 21: The larva of the Rhinoceros Beetle.--_Translator's Note_.]

[Footnote 22: For the Pompilus, or Ringed Calicurgus, cf. _The Life and Love of the Insect_: chap. xii.--_Translator's Note_.]

[Footnote 23: For the Narbonne Lycosa, or Black-bellied Tarantula, cf.

_The Life of the Spider_: chaps. i. and iii. to vii.--_Translator's Note_.]

[Footnote 24: Cf. _The Life of the Fly_: chap. i.--_Translator's Note_.]

For producing variations of animal species to suit our theorists there is nothing so convenient as the influence of environment. It is a vague, elastic phrase, which does not compromise us by compelling us to be too precise and it supplies an apparent explanation of the inexplicable. But is this influence so powerful as they say?

I grant you that to some small extent it modifies the shape, the fur or feather, the colouring, the outward accessories. To go farther would be to fly in the face of facts. If the surroundings become too exacting, the animal protests against the violence endured and succ.u.mbs rather than change. If they go to work gently, the creature subjected to them adapts itself as best it can, but invincibly refuses to cease to be what it is. It must live in the form of the mould whence it issued, or it must die: there is no other alternative.

Instinct, one of the higher characteristics, is no less rebellious to the injunctions of environment than are the organs, which serve its activity. Innumerable guilds divide the work of the entomological world; and each member of one of these corporations is subject to rules which not climate, nor lat.i.tude, nor the most serious disturbances of diet are able to alter.

Look at the Dung-beetles of the pampas. At the other end of the world, in their vast flooded pastures, so different from our scanty greenswards, they follow, without notable variations, the same methods as their colleagues in Provence. A profound change of surroundings in no way effects the fundamental industry of the group.

Nor do the provisions available affect it. The staple food to-day is matter of bovine origin. But the Ox is a newcomer in the land, an importation of the Spanish conquest. What did the Megathopae, the Bolbites, the Splendid Phanaeus eat and knead, before the arrival of the present purveyor? The Llama, that denizen of the uplands, was not able to feed the Dung-beetles confined to the plains. In days of old, the foster-father was perhaps the monstrous Megatherium, a dung-factory of incomparable prodigality.

And from the produce of the colossal beast, whereof naught remains but a few rare skeletons, the modellers pa.s.sed to the produce of the Sheep and the Ox, without altering their ovoids or their gourds, even as our Sacred Beetle, without ceasing to be faithful to her pear, accepts the Cow's flat cake in the absence of the favourite morsel, the Sheep's bannock.

In the south as in the north, at the antipodes as here, every Copris fas.h.i.+ons ovoids with the egg at the smaller end; every Sacred Beetle models pears or gourds with a hatching-chamber in the neck; but the materials employed vary greatly according to the season and locality and can be furnished by the Megatherium, the Ox, the Horse, the Sheep or by man and several others.

We must not allow this diversity to lead us to believe in changes of instinct: that would be to strain at a Gnat and swallow a Camel. The industry of the Megachiles, for instance, consists of manufacturing wallets with bits of leaves; that of the Cotton-bees of making bags of wadding with the flock gathered from certain plants. Whether the pieces be cut from the leaves of this shrub or that, or at need from the petals of some flower; whether the cotton-wool be collected here or there, as chance may direct the encounter, the industry undergoes no essential changes.

In the same manner, nothing changes in the art of the Dung-beetle, victualling himself with materials in this mine or that. Here in truth we have immutable instinct, here we behold the rock which our theorists are unable to shake.

And why should it change, this instinct, so logical in its workings?

Where could it find, even with chance a.s.sisting, a better plan? In spite of an equipment which varies in the different genera, it suggests to every modelling Dung-beetle the spherical shape, a fundamental structure which is hardly affected when the egg is placed in position.

From the outset, without the use of compa.s.ses, without any mechanical rolling, without s.h.i.+fting the thing on its base, one and all obtain the ball, the delicately executed compact body supremely favourable to the grub's well-being. To the shapeless lump, demanding no pains, they all prefer the sphere, lovingly fas.h.i.+oned and calling for much manipulation, the globe which is the preeminent form and best-adapted for the preservation of energy, in the case of a sun and of a Dung-beetle's cradle alike.

When Macleay[25] gave the Sacred Beetle the name of Heliocantharus, the Black-beetle of the Sun, what had he in mind? The radiating denticulations of the forehead, the insect's gambols in the bright sunlight? Was he not thinking rather of the symbol of Egypt, the Scarab who, on the pediment of the temples, lifts towards the sky, by way of a pill, a vermilion sphere, the image of the sun?

[Footnote 25: William Sharp Macleay (1792-1865), author of _Horae Entomologicae_; or, _Essays on Annulose Animals_ (1819-1821), on which I quote the _Dictionary of National Biography_:

"He propounded the circular or quinary system, a forcedly artificial attempt at a natural system of cla.s.sification, which soon became a byword among naturalists."--_Translator's Note_.]

The comparison between the mighty bodies of the universe and the insect's humble pellet was not distasteful to the thinkers on the banks of the Nile. For them supreme splendour found its effigy in extreme abjection. Were they very wrong?

No, for the pill-roller's work propounds a grave problem to whoso is capable of reflection. It compels us to accept this alternative: either to credit the Dung-beetle's flat head with the signal honour of having of itself solved the geometrical problem of preserved food, or else to fall back upon a harmony ruling all things under the eye of an Intelligence Which, knowing everything, has provided for everything.

CHAPTER X INSECT COLOURING

_Phanaeus splendidulus_, the glittering, the resplendent: this is the epithet selected by the official nomenclators to describe the handsomest Dung-beetle of the pampas. The name is not at all exaggerated. Combining the fire of gems with metallic l.u.s.tre, the insect, according to the incidence of the light, emits the green reflections of the emerald or the gleam of ruddy copper. The muck-raker would do honour to the jeweller's show-cases.

For the rest, our own Dung-beetles, though usually modest in their attire, also have a leaning toward luxurious ornament. One Onthophagus decorates his corselet with Florentine bronze; another wears garnets on his wing-cases. Black above, the Mimic Geotrupes is the colour of copper pyrites below; also black in all parts exposed to the light of day, the Stercoraceous Geotrupes displays a ventral surface of a glorious amethyst violet.

Many other series, of greatly varied habits, Carabi,[1] Cetoniae, Buprestes, Chrysomelae,[2] rival and even surpa.s.s the magnificent Dung-beetles in the matter of jewellery. At times we encounter splendours which the imagination of a lapidary would not venture to depict. The Azure Hoplia,[3] the inmate of the osier-beds and elders by the banks of the mountain streams, is a wonderful blue, tenderer and softer to the eye than the azure of the heavens. You could not find an ornament to match it save on the throats of certain Humming-birds and the wings of a few b.u.t.terflies in equatorial climes.

[Footnote 1: Cf. Chapter XIV. of the present volume.--_Translator's Note_.]

[Footnote 2: Golden Apple-beetles.--_Translator's Note_.]

[Footnote 3: A genus of c.o.c.kchafer. Cf. _The Life of the Fly_: chap.

vii.--_Translator's Note_.]

To adorn itself like this, in what Golconda does the insect gather its gems? In what diggings does it find its gold nuggets? What a pretty problem is that of a Buprestis' wing-case! Here the chemistry of colours ought to reap a delightful harvest; but the difficulties are great, it seems, so much so that science cannot yet tell us the why and the wherefore of the humblest costume. The answer will come in a remote future, if indeed it ever comes completely, for life's laboratory may well contain secrets denied to our retorts. For the moment, I shall perhaps be contributing a grain of sand to the future palace if I describe the little that I have seen.

My basic observation dates a long way back. I was at that time busy with the Hunting Wasps, following their larval development from the egg to the coc.o.o.n. Let us take an instance from my notes, which cover nearly all the game-hunters of my district. I will choose the larva of the Yellow-winged Sphex,[4] which, with its convenient size, will furnish an easy object-lesson.

[Footnote 4: Cf. _The Hunting Wasps_: chap. iv.--_Translator's Note_.]

Under the transparent skin of the larva, which has been recently hatched and is consuming its first Cricket, we soon perceive some fine white spots, which rapidly increase in size and number and eventually cover the whole body, except the first two or three segments. On dissecting the grub, we find that these spots have to do with the adipose layer, of which they form a considerable part, for, far from being scattered only on the surface, they run through its whole thickness and are present in such numbers that the forceps cannot seize the least fragment of this tissue without picking up a few of them.

Though perfectly visible without the help of a lens, these puzzling spots call for the microscope if we wish to study them in detail. We then find that the adipose tissue is made up of two kinds of vesicles: some, bright yellow and transparent, are filled with oily drops; the rest, opaque and starch-white, are distended with a very fine powder, which spreads in a cloudy trail when the vesicle containing it is broken on the object-slide. Intermingled without apparent order, the two kinds of bags are of the same shape and the same size. The first go to make up the nutritive reserves, the fatty tissue properly so-called; the second form the white dots which we will study for a moment.

An inspection under the microscope tells us that the contents of the white cells are composed of very fine, opaque grains, insoluble in water and of greater density. The use of chemical reagents on the object-slide proves that nitric acid dissolves these grains, with effervescence and without leaving the least residue, even when they are still enclosed in their vesicles. On the other hand, the true fatty cells suffer in no way when attacked by this acid; they merely turn a little yellower.

Let us take advantage of this property to operate on a larger scale.

The adipose tissue taken from a number of larvae is treated with nitric acid. The effervescence is as lively as if the reaction were taking effect on a bit of chalk. When it has subsided, some yellow clots are floating on the surface. These are easily separated. They come from the fatty substance and the cellular membranes. There remains a clear liquid containing the white granules in solution.

The riddle of these granules was being presented to me for the first time; my predecessors had provided no physiological or anatomical data to guide me; great therefore was my joy when, after a little fumbling, I succeeded in hitting upon their characteristic feature.

The solution is evaporated in a small porcelain capsule, placed on the hot embers. On the residue I pour a few drops of ammonia, or else simply water. A glorious crimson colour at once makes its appearance.

The problem is solved: the colouring-matter which has just formed is murexide; and consequently the powdery substance which filled the cells was none other than uric acid, or more precisely ammonium urate.

A physiological fact of this importance can hardly stand alone.

Indeed, since this basic experiment I have discovered grains of uric acid in the adipose tissue of the larvae of all the Hunting Wasps of our parts, as well as in the Bees at the moment of the nymphosis. I have observed them in many other insects, either in the larval or in the perfect state; but in this respect there is none to equal the grub of the game-hunting Wasp, which is all speckled with white. I think I see the reason.

Let us consider two larvae which eat live prey: that of the Sphex and that of the Hydrophilus.[5] Uric acid, the inevitable product of the vital transformations, or at all events one of its a.n.a.logues, must be formed in both. But the Hydrophilus' larva shows no acc.u.mulation of it in its adipose layer, whereas the Sphex' is full of it.

[Footnote 5: The Great Water-beetle.--_Translator's Note_.]