THE DORTHESIA

After the exodus of the young, when she deserts her tent of swansdown, half a finger’s-breadth in thickness, very warm and soft, but blocked with rubbish which would hamper a second family, the Clotho Spider1 proceeds to fashion elsewhere a light hammock with a canopy, an inexpensive summer-house where she will pass the remainder of the warm weather. Those who are not yet marriageable ask no better protection against the inclemencies of the winter; their robust powers of endurance are satisfied with a muslin tent under the shelter of a stone.

The matrons, on the other hand, as the heat begins to decrease, hasten to enlarge and strengthen their cells, lavishing upon them the contents of their silk-reservoirs, which the hunting-expeditions of the fine summer [291]nights have left distended. When the sharp white-frosts set in they will doubtless find more comfort in their luxurious mansions than in the first rickety hovels; nevertheless, they do not build them precisely for themselves but rather for the use of their expected offspring; wherefore the walls are never stout nor the feather-beds downy enough.

The superb structure of the Clotho is above all a nest, beside which those of the Chaffinch and the Siskin are but squatter’s huts. The mother, it is true, does not sit upon her eggs, being as she is without an incubator; she does not feed her offspring, who for that matter do not require her assistance; but the part which she plays is, none the less, one of exquisite tenderness. For seven or eight months she watches over her brood, protecting it with a devotion equal to that of the bird, or even greater.

Maternity, the supreme inspiration of the noblest instincts, has thousands upon thousands of masterpieces to bear witness to its skill. Let us recall that of the Labyrinth Spider.2 What a wonderful achievement is [292]the spacious building where the mother mounts guard about the star-shaped tabernacle, the family cradle! What an eminently logical stronghold is this rampart of silk reinforced by masonry, to protect the eggs from the probe of the Ichneumon-fly!

Similarly, each mother has her own defensive methods, which are sometimes the most ingenious inventions and sometimes devices of extreme simplicity. The strange thing is that the distribution of talents takes no account whatever of the insect hierarchy. Certain insects of the highest rank, protected by sumptuous wing-cases, or sporting lofty plumes, or attired in garments of imbricated gold scales, are almost or quite incapable of doing anything; they are magnificent duffers, whereas others, among the very humblest, and passing unperceived, amaze us by their talents when we grant them our attention.

But do not things happen likewise amongst ourselves? True merit shuns indolent luxury. If we are to turn to the best advantage the little good which may lie hidden within us, we must feel the incentive of need. [293]As long as nineteen centuries ago, Persius prefaced his satires with the lines:

Magister artis ingenique largitor Venter.

One of our proverbs repeats his views in terms a little less crude:

L’homme est comme la nèfle; il n’est rien qui vaille

S’il n’amûri longtemps au grenier, sur la paille.3

Insects are like ourselves. Necessity stimulates their wits and at times enables them to make discoveries which upset all our conceptions. I know of one, amongst the humblest and least well-known, which, to safeguard its progeny, has found the following strange solution of the problem: at the laying-season, the normal length of the body is trebled: the fore part is left at the service of the insect, which feeds, digests, roams about and shares in the joys of the sunlight; [294]and the hinder part becomes an infant’s crêche, a nursery in which the little ones are gently exercised.

This singular creature is called the Dorthesia (D. Characias, Latt). We find it from time to time on the Greater Spurge, which the Greeks used to call Characias and which the Provençal peasant of to-day calls Chusclo, Lachusclo.

A lover of the climate in which the olive flourishes, this spurge abounds on the Sérignan hills, in the driest spots, where its great blue-green tufts contrast with the poverty-stricken vegetation of the neighbourhood. Standing in a bed of pebbles which reflect the sun’s rays upon it, by its vigorous foliage it protests against the hardships of winter. Still, it is not devoid of prudence. When the foolish almond-tree is already abandoning its shivering petals to the north-east wind, the spurge, less hasty, continues to observe the weather and keeps the tender tips of its blossoms rolled up crosier-wise for protection. The worst frosts are over. Then, with a sudden urge of sap, the stems swell with a milk that burns like hot coals and the crosiers uncurl and straighten out into clusters of [295]dingy little flowers, at which the first Gnats of the year come to slake their thirst.

Wait a few days longer. As the weather grows milder, we shall see a numerous population slowly emerging from the heap of leaves that have fallen at the foot of the spurge. It is the Dorthesia quitting her winter quarters under the remnants of the old foliage, and climbing, gradually, by cautious stages, from the base to the topmost summits of the plant, where the joys of heat and radiant light await her, together with the delights of an inexhaustible feeding-bottle.

In April, or at latest in May, the ascent is completed; all the little creatures are assembled on the topmost tips of the branches, in close-packed groups, side touching side, after the fashion of the Plant-lice. A sap-drinker and endowed with a beak that acts as a gimlet, the Dorthesia is, in fact, related to the Aphides, whose sedentary and social habits she shares; but, far from reminding us in appearance of the plump, naked vermin which the rose-tree and so many other plants have made familiar to us, she is clothed, and her costume is one of unusual elegance.[296]

The orange Terebinth-lice, imprisoned in galls, whether horn-shaped or rounded like apricots, attach to their hinder parts a long train of extreme delicacy, which the slightest touch reduces to dust. In the Dorthesiæ, on the other hand, we see a complete garment, a close-fitting coat of indefinite length, though fragile and breaking off in particles under the point of a needle, just as a brittle rind might do.

Nothing could be prettier than the cloak of this large Louse, either in shape or in colour. It is a uniform dead white, more pleasing to the eye than even the white of milk. The forepart of the garment is a jacket of curly knots arranged in four longitudinal rows between which other, smaller knots are distributed. The hinder part is a fringe of ten slats gradually increasing in width and spreading outwards, not unlike the teeth of a comb. The breast is covered by a shirt-front formed of symmetrical plates and pierced with six neatly-rounded holes, through which the brown legs emerge, quite naked and unconstrained. This shirt-front and the curly mantle on the back together form a sort of sleeveless woollen waistcoat [297]with easy-fitting armholes. In the same way the hood is pierced by holes to give free play to the rostrum and the antennæ. All the other parts are covered by the white cloak.

This is the winter costume; it covers the whole body but does not extend beyond it. Later, when the laying-season draws near, the garment grows longer, as though the insect, which in reality cannot undergo further change, were growing at a furious rate and trebling its length. Gracefully curved like the prow of a gondola, the new portion is furrowed above by wide parallel grooves; underneath it is finely streaked, almost smooth. The end is cut off square. The magnifying-glass here reveals a transverse button-hole plugged with fine cotton-wool.

The material of the garment is everywhere brittle, fusible and inflammable; when laid on paper it leaves a slightly translucent mark. From these qualities we judge it to be a sort of wax, similar to beeswax. In order to obtain it in some other form than that of tiny particles removed from the insect, I collect a handful of Dorthesiæ and subject them to the action of boiling water. The waxen coverings melt and dissolve into [298]an oily liquid which floats on the surface; the denuded insects sink to the bottom. On cooling, the thin floating layer sets into an amber-yellow sheet.

This colour causes us a certain surprise. We began with a substance whose whiteness rivalled that of milk; and now melting gives it a look of resin. This is a matter of molecular arrangement and nothing more. To impart a proper whiteness to the yellow wax as it comes from the hive, the wax-chandler melts it down and pours the melted substance into cold water, thereby reducing it to thin flakes which he afterwards exposes, on wattled screens, to the rays of the sun. Further meltings follow, with a further production of shell-like flakes and further exposure to the bright sunshine; and, little by little, the wax turns white by changing its molecular structure. In this art of bleaching how far our superior is the Dorthesia! Without treating the material by repeated meltings and prolonged exposures to the sun, she then and there transforms a yellow wax into one of incomparable whiteness. She obtains by her gentle methods a result [299]that eludes the violent procedures of the laboratory.

Like beeswax, the Dorthesia’s wax is not collected in the outer world: it is a first product, exuded through the surface of the body. No manipulation is required to induce it to form itself into curly knots, to fall into uniform streaks or graceful flutings. Merely in exuding from the pores of the skin, it automatically acquires the requisite form; like the fledgling’s plumage, its clothing grows correctly by the mere activities of the organism; the wearer of the dress has no need to improve upon it.

The tiny creature, when it issues from the egg, is perfectly naked, and brown in colour. Soon, before leaving the mother and settling on the bark of the spurge to draw its first sips, it becomes covered with thinly-scattered white specks, which form the first outline of the future jacket. By slow degrees these specks increase in number and are produced into curly knots, so much so that the youngster, at the moment of its emancipation, is clad like its elders.

The exudation of the wax is continuous; [300]the white tunic is constantly growing larger and nearer to perfection. Therefore the insect, if I cunningly strip it bare, ought to be capable of clothing itself anew. Experiment confirms my expectations. Destroying her garments with the point of a needle and brushing them off with a camel-hair pencil, I completely denude a mature Dorthesia. The persecuted Louse comes forth in her poor brown skin. I isolate her on a sprig of spurge. In two or three weeks’ time the coat has been remade; not so full as the first, but large enough and of the regulation cut. With the wax which would have added to the original garment the insect has sweated forth another.

What is the use of this backward prolongation which trebles the actual size of the body? Is it merely an adornment? It is much more than that.

Let us, once April is here, detach and lay open this strange appendage. It is hollow, and full of an incomparable downy wadding; no feather-bed or eider-down could boast of so fine, so white a filling. In the midst of this magnificent eider-down some ovoid beads are scattered, some white and others [301]tinged with a ruddy brown. These are the eggs. The new-born insects are swarming amongst them, higgledy-piggledy; some are bare and brown, some are more or less speckled with white, according to the more or less advanced state of the coat.

On the other hand, let us watch the Dorthesia idly roaming about the spurge. At long intervals we shall see emerging from the orifice at the end of the padded pocket a young Louse, handsomely clad, and nimble in his movements, who chooses his place beside his mother and settles down, plunging his bill into the juicy bark. He will not stir again until the well is dry. Others follow him from day to day; and this goes on for months on end!

If we were guided only by these observations we should conclude that the mother was viviparous, given to dropping, here and there, living offspring, all ready dressed. Nothing of the kind: we have just found in the thickly-quilted pocket both eggs and young. Moreover, the laying and hatching of the eggs may be witnessed without difficulty.

In a glass tube provided with a sprig of spurge I segregate a few mothers whose [302]terminal wallet I have removed. Laid bare, the insect’s hind-quarters have no further secrets from us; I see, sprouting from them, a sort of white mildew, like an unshaven beard. This is the waxy secretion that sprouts from the insect’s hind-quarters, producing, instead of tassels, filaments of extreme fineness. It is thus that the down which fills the wallet must be produced. Presently, in the midst of this tuft of down, an egg appears, like those which we obtained by breaking into the maternal treasury.

This method enables me to estimate the size of the clutch. Two Dorthesiæ stripped bare behind and isolated, with provisions, in a glass tube, produced, in thirteen days, thirty eggs, or fifteen apiece, or rather more than one egg daily. As the process of laying continues for nearly five months, the total number of eggs for a single mother must be nearly two hundred.

The eggs hatch in three or four weeks’ time. The hatching is announced by a change in the colour of the egg, which from white becomes a bright reddish-brown. On leaving the egg-shell the infant Louse is reddish-brown and absolutely naked. Its appearance [303]is that of a very tiny Spider, the more so as its long antennæ look very like a fourth pair of legs. Before long, four longitudinal rows of tiny white tufts appear on its back, with bare spaces between them. This is the beginning of the waxen mantle.

The protracted period of egg-laying, which continues for four months or more, the comparatively quick hatching, and, finally, the gradual exudation of the Louse’s clothing, explain why white eggs and reddish-brown eggs, with naked youngsters and others more or less clothed, are found simultaneously in the maternal pouch. This pouch is a warehouse in which the Louse’s eggs are collected for months together.

Inside the pouch, in the depths of its luxurious padding, the young Lice are born, grow up, and clothe themselves in wax before risking the dangers of the open. The mother gently carries them from twig to twig of the spurge without troubling herself as to those that emerge from her pouch. One by one, as they feel themselves strong enough, they migrate, when their time has come, to settle down in the neighbourhood. The exit from their home is always open; [304]they have only to force their way through the barrier of down.

The Narbonne Lycosa carries her family about with much less tenderness and security. There is no shelter on the back of the Gipsy Spider, no safeguard against falls, which are frequent in such a scramble. The Dorthesia, more happily inspired, makes a box of the skirts of her mantle and a downy bed of her caudal tufts. To find an equivalent method we must go back from the Spurge-louse to the first-born of the Mammifers—Kangaroos, Opossums and others—who rear their young in a pouch formed by a fold of the skin of the abdomen. Coming before its time, the shapeless embryo fixes itself on the teat and completes its development in the maternal pouch or marsupium.

Let us make use of this term to denote the Dorthesia’s pouch. There is a great similarity between the two wallets, although the insect is superior to the mammal in this respect: Life often begins with excellence in the lowly and ends with mediocrity in the strong. In the original device of the marsupium [305]a Louse has done better than the Opossum.

With the object of following the history of my insects more conveniently than was possible under the blaze of the sun by the roadside, I placed before one of my study windows a fine clump of spurge transplanted into a capacious flowerpot. As a result of my diligence the plant was populated during the course of March by three or four dozen Dorthesiæ, all wearing more or less fully developed marsupia. My experiment in the domestication of plant and insect was extremely successful: the spurge did well, so its inhabitants prospered also.

The wallets became filled with eggs and then with young Lice, who, matured in the nick of time, and more numerous every day, emerged and spread themselves at will over the spurge. During the heat of the summer you might have thought it had snowed on the plant, so populous was the colony of white Lice. It contained thousands of new inhabitants, varying in size and easily distinguished from the mothers and foundresses by their smaller dimensions, but above all by the [306]complete absence of the marsupium, an addition which must develop very much later, after hibernation at the root of the food-plant.

Some are larger and others smaller, according to age, for the matrons still continue to procreate, but all wear the same costume and present the same appearance; yet certain differences, unnoticed at the time of my summary examination, should divide them into two groups, one very small, consisting almost wholly of exceptions, and the other forming the vast majority.

In August these differences become very plainly visible. On the tips of the leaves, here and there, are isolated a few Lice who are surrounding themselves with a fragile waxen enclosure, a sort of shapeless capsule, while the rest of the flock, nearly all, in fact, continue to drink, their bills plunged into the bark. Who are these solitaries, withdrawn from the world of drinkers? They are males, undergoing transformation. I open some of these fragile capsules. In the centre, on a downy bed like that which fills the wallets of the mothers, lies a nymph endowed with wing-stumps. At the beginning [307]of September I obtain the first males in their perfect state.

Strange creatures, in truth! Standing high on their legs, with long horns, they have the look of certain Bugs. The body is black and powdered with a fine waxy powder, the remains of the capsule in which the transformation took place. The wings are of a leaden grey, rounded at the tips, overlapping one another when at rest and protruding a long way beyond the extremity of the abdomen. To the rear is an aigrette of white filaments, very long and straight, composed, no doubt, of wax, like the cloak of the larval stage. It is a very fragile ornament: the insect loses most of it merely in wandering about among the few leaves in his glass prison, the tube in which I am observing him.

In moments of elation the tip of the abdomen rises between the lifted wings and the bundle of spokes spreads out fanwise. The insect is showing off, erecting his tail, like the peacock. To glorify his nuptials, he has attached a comet’s tail to his rump; he displays it fanwise, closes it, opens it again, making it quiver and glisten in the sunlight. [308]When the crisis of joy has passed his finery is folded up and the abdomen sinks down under cover of the wings.

The head is small, with long antennæ. At the tip of the abdomen is a short, pointed projection, a sort of hook, an implement of pairing. Of mouth-parts or rostrum there is absolutely not a trace. What would he do with them, this microcephalous coxcomb? He has changed his shape only to flirt for a moment with his neighbours of the other sex, to mate and to die. Moreover, the part which he fulfils does not seem to be particularly necessary. On the spurge in my study the female population of the second generation numbers several thousands, and I obtain, in all, some thirty males. Approximately, there are a hundred times as many females. The dandified wearers of the aigrette cannot suffice for such a harem.

On the other hand, they do not seem to be very eager. I see some who, on emerging from the ruins of their capsule, covered with powder, brush and wipe themselves a little, try their wings, and then, with a lazy flight, make for the window, which is closed to prevent their escape. The festival of the sunlight [309]is to them a greater attraction than the emotions of pairing. It is possible that the indifferent lighting of the room is in this case the cause of their coldness. In the open country, under the direct rays of the sun, they would certainly have displayed their finery amidst the marriageable females, and the business of pairing would not have lacked ardour. But even though the most favourable circumstances had conditioned the pairing, the exaggerated number of females, out of all proportion to the males, tells us that very few are chosen among many that are called: roughly about one in a hundred. Nevertheless, all produce offspring. With these singular creatures it is enough that a few mothers are fecundated from time to time, and the race continues to thrive. The impulse communicated to the elect is a heritage which is handed down for some considerable time, on condition that a few couples, year by year, restore to the community its exhausted energies.

A parasite frequently observed in Bee-hives, the Monodontomerus, has already shown us a similar example of the rarity of the males. Two tiny little creatures tell us [310]of a vast field yet to be tilled by our genetic theories. One day, perhaps, they will help us to unravel the obscure problem of the sexes.

Meanwhile the old mothers, the Dorthesiæ bearing the marsupium, grow day by day fewer on the spurge. Their ovaries exhausted and their wallets empty, they fall to the ground, where the Ants cut them to pieces. On the plant only those young mothers whose maternal pouches will not begin to make an appearance until the return of spring are visible nearly till Christmas. When the cold becomes severe the flock descends to the foot of the spurge, under the heap of dead leaves. They will come up again at the end of March, slowly climbing the spurge-plant, to acquire the rearing-pouch and begin once again the cycle of evolution.