Social Life in the Insect World Part 7

2. TRANSVERSE SECTION OF THE SAME.

3, 3a. NEST OF EMPUSA PAUPERATA.

4. TRANSVERSE SECTION OF THE SAME.

5. VERTICAL SELECTION OF THE SAME.

6. NEST OF THE GREY MANTIS.

7. SCHEFFER'S SISYPHUS (see Chap. XII.)

8. PELLET OF THE SISYPHUS.

9. PELLET OF THE SISYPHUS WITH DEJECTA OF THE LARVA FORCED THROUGH THE WALLS.]

To be present at the construction of the nest--to learn how the Mantis contrives to build so complex a structure--such was the main point of my researches. I succeeded, not without difficulty, as the eggs are laid without warning and nearly always at night. After a great deal of futile endeavour, chance at last favoured me. On the 5th of September one of my guests, fecundated on the 29th of August, began to make her preparations under my eyes, at four o'clock in the afternoon.

One remark before proceeding: all the nests I have obtained in the laboratory--and I have obtained a good number--have without exception been built upon the wire gauze of the covers. I have been careful to provide the insects with roughened stones and tufts of thyme, both being very commonly used as foundations in the open fields. The captives have always preferred the network of wire gauze, which affords a perfectly firm foundation, as the soft material of the nest becomes incrusted upon the meshes as it hardens.

In natural conditions the nests are never in any way sheltered; they support the inclemencies of winter, resist rain, wind, frost, and snow, without becoming detached. It is true that the female always selects an uneven support on which the foundations of the nest can be shaped, thus obtaining a firm hold. The site chosen is always the best obtainable within reach, and the wire gauze is constantly adopted as the best foundation obtainable in the cages.

The only Mantis that I was able to observe at the moment of laying her eggs worked upside-down, clinging to the wire near the top of the cover.

My presence, my magnifying-gla.s.s, my investigations did not disturb her in the least, so absorbed was she in her labours. I was able to lift up the dome of wire gauze, tilt it, reverse it, turn it over and reverse it again, without causing the insect to delay her task for a moment. I was able, with my tweezers, to raise the long wings in order to observe rather more closely what was taking place beneath them; the Mantis took absolutely no notice of me. So far all was well; the female did not move, and lent herself impa.s.sively to all the indiscretions of the observer. Nevertheless, matters did not proceed as I had wished, so rapid was the operation and so difficult observation.

The end of the abdomen is constantly immersed in a blob of foam, which does not allow one to grasp the details of the process very clearly.

This foam is of a greyish white, slightly viscous, and almost like soapsuds. At the moment of its appearance it adheres slightly to the end of a straw plunged into it. Two minutes later it is solidified and no longer adheres to the straw. In a short time its consistency is that of the substance of an old nest.

[Ill.u.s.tration: 1. THE MANTIS DEVOURING THE MALE IN THE ACT OF MATING.

2. THE MANTIS COMPLETING HER NEST.

3. GOLDEN SCARABaeI CUTTING UP A LOB-WORM.]

The foamy ma.s.s consists chiefly of air imprisoned in minute bubbles.

This air, which gives the nest a volume very much greater than that of the abdomen of the Mantis, evidently does not issue from the insect although the foam appears at the orifice of the genital organs; it is borrowed from the atmosphere. The Mantis builds more especially with air, which is eminently adapted to protect the nest against changes of temperature. She emits a glutinous substance like the liquid secretion of silk-worms, and with this composition, mixed instantaneously with the outer air, she produces the foam of which the nest is constructed.

She whips the secretion as we whip white of egg, in order to make it rise and stiffen. The extremity of the abdomen opens in a long cleft, forming two lateral ladles which open and shut with a rapid, incessant movement, beating the viscous liquid and converting it into foam as it is secreted. Beside the two oscillating ladles we see the internal organs rising and falling, protruding and retreating like a piston-rod, but it is impossible to observe the precise nature of their action, bathed as they are in the opaque blob of foam.

The end of the abdomen, continually palpitating, rapidly closing and opening its valves, oscillates right and left like a pendulum. From each of these oscillations results a layer of eggs in the interior, and a transversal crevice on the exterior. As it advances in the arc described, suddenly, and at frequent intervals, it plunges deeper into the foam, as though burying something at the bottom of the frothy ma.s.s.

Each time it does so an egg is doubtless deposited; but the operation is so rapid, and takes place under conditions so unfavourable for observation, that I have never once been enabled to see the oviduct at work. I can only judge of the advent of the eggs by the movements of the end of the abdomen, which is immersed more deeply with a sudden plunging movement.

At the same time the viscous composition is emitted in intermittent waves, and is beaten into a foam by the terminal valves. The foam thus obtained spreads itself over the sides and at the base of the layer of eggs, and projects through the meshes of the wire gauze as a result of the pressure of the abdomen. Thus the spongy envelope is progressively created as the ovaries are gradually emptied.

I imagine, although I cannot speak as the result of direct observation, that for the central core, where the eggs are surrounded by a material more h.o.m.ogeneous than that of the outer sh.e.l.l, the Mantis must employ her secretion as it emerges, without beating it into a foam. The layer of eggs once deposited, the two valves would produce the foam required to envelop the eggs. It is extremely difficult, however, to guess what occurs beneath the veil of foam-like secretion.

In a recent nest the zone of issue is surrounded by a layer of finely porous matter, of a pure matt, almost chalky white, which contrasts distinctly with the remainder of the nest, which is of a dirty white. It resembles the icing composition made by confectioners with whipped white of egg, sugar, and starch, for the ornamentation of cakes.

This snowy border is easily crumbled and easily detached. When it disappears the zone of issue is clearly defined, with its double series of leaves with free edges. Exposure to the weather, wind, and rain result in its disappearance, fragment by fragment, so that old nests preserve no trace of it.

At first sight one is tempted to regard this snowy substance as of a different material to the rest of the nest. But does the Mantis really employ two secretions? No. Anatomy, in the first place, a.s.sures us of the unity of the materials of the nest. The organ which secretes the substance of the nest consists of cylindrical tubes, having a curious tangled appearance, which are arranged in two groups of twenty each.

They are all filled with a colourless, viscous fluid, which is precisely similar in appearance in all parts of the organ. There is no indication of any organ or secretion which could produce a chalky coloration.

Moreover, the method by which the snowy band is formed rejects the idea of a different material. We see the two caudal appendices of the Mantis sweeping the surface of the foamy ma.s.s, and skimming, so to speak, the cream of the cream, gathering it together, and retaining it along the hump of the nest in such a way as to form a band like a ribbon of icing.

What remains after this scouring process, or what oozes from the band before it has set, spreads over the sides of the nest in a thin layer of bubbles so fine that they cannot be distinguished without the aid of a lens.

We often see a torrent of muddy water, full of clay in suspension, covered with great streaks and ma.s.ses of foam. On this fundamental foam, so to call it, which is soiled with earthy matters, we see here and there ma.s.ses of a beautiful white foam, in which the bubbles are much smaller. A process of selection results from variations in density, and here and there we see foam white as snow resting on the dirty foam from which it is produced. Something of the kind occurs when the Mantis builds her nest. The two appendices whip the viscous secretion of the glands into foam. The lightest portion, whose bubbles are of the greatest tenuity, which is white on account of its finer porosity, rises to the surface, where the caudal filaments sweep it up and gather it into the snowy ribbon which runs along the summit of the nest.

So far, with a little patience, observation is possible and yields a satisfactory result. It becomes impossible in the matter of the complex central zone, where the exits for the larvae are contrived through the double series of overlapping leaves. The little I have been able to learn amounts to this: The end of the abdomen, deeply cleft in a horizontal direction, forms a kind of fork, of which the upper extremity remains almost motionless, while the lower continuously oscillates, producing the foam and depositing the eggs. The creation of the central zone is certainly the work of the upper extremity.

It is always to be seen in the continuation of this central zone, in the midst of the fine white foam gathered up by the caudal filaments. The latter delimit the zone, one working on either side, feeling the edges of the belt, and apparently testing it and judging its progress. These two filaments are like two long fingers of exquisite sensitiveness, which direct the difficult operation.

But how are the two series of scales obtained, and the fissures, the gates of exit which they shelter? I do not know; I cannot even imagine.

I leave the end of the problem to others.

What a wonderful mechanism is this, that has the power to emit and to form, so quickly and methodically, the h.o.r.n.y medium of the central kernel, the foam which forms the protective walls, the white creamy foam of the ribbon which runs along the central zone, the eggs, and the fecundating liquid, while at the same time it constructs the overlapping leaves, the imbricated scales, and the alternating series of open fissures! We are lost in the face of such a wonder. Yet how easily the work is performed! Clinging to the wire gauze, forming, so to speak, the axis of her nest, the Mantis barely moves. She bestows not a glance on the marvel which is growing behind her; her limbs are used only for support; they take no part in the building of the nest. The nest is built, if we may say so, automatically. It is not the result of industry and the cunning of instinct; it is a purely mechanical task, which is conditioned by the implements, by the organisation of the insect. The nest, complex though it is in structure, results solely from the functioning of the organs, as in our human industries a host of objects are mechanically fashioned whose perfection puts the dexterity of the fingers to shame.

From another point of view the nest of the Mantis is even more remarkable. It forms an excellent application of one of the most valuable lessons of physical science in the matter of the conservation of heat. The Mantis has outstripped humanity in her knowledge of thermic nonconductors or insulators.

The famous physicist Rumford was responsible for a very pretty experiment designed to demonstrate the low conductivity of air where heat other than radiant heat is concerned. The famous scientist surrounded a frozen cheese by a ma.s.s of foam consisting of well-beaten eggs. The whole was exposed to the heat of an oven. In a few minutes a light omelette was obtained, piping hot, but the cheese in the centre was as cold as at the outset. The air imprisoned in the bubbles of the surrounding froth accounts for the phenomenon. Extremely refractory to heat, it had absorbed the heat of the oven and had prevented it from reaching the frozen substance in the centre of the omelette.

Now, what does the Mantis do? Precisely what Rumford did; she whips her alb.u.men to obtain a soufflee, a froth composed of myriads of tiny air-bubbles, which will protect the germs of life contained in the central core. It is true that her aim is reversed; the coagulated foam of the nest is a safeguard against cold, not against heat, but what will afford protection from the one will afford protection from the other; so that Rumford, had he wished, might equally well have maintained a hot body at a high temperature in a refrigerator.

Rumford understood the athermic properties of a blanket of air-cells, thanks to the acc.u.mulated knowledge of his predecessors and his own studies and experiments. How is it that the Mantis, for who knows how many ages, has been able to outstrip our physicists in this problem in calorics? How did she learn to surround her eggs with this ma.s.s of solidifying froth, so that it was able, although fixed to a bough or a stone without other shelter, to brave with impunity the rigours of winter?

The other Mantes found in my neighbourhood, which are the only species of which I can speak with full knowledge, employ or omit the envelope of solidifying froth accordingly as the eggs are or are not intended to survive the winter. The little Grey Mantis (_Ameles decolor_), which differs so widely from the Praying Mantis in that the wings of the female are almost completely absent, builds a nest hardly as large as a cherry-stone, and covers it skilfully with a porous rind. Why this cellular envelope? Because the nest of the _Ameles_, like that of the Praying Mantis, has to endure through the winter, fixed to a stone or a twig, and is thus exposed to the full severity of the dangerous season.

The _Empusa pauperata_, on the other hand (one of the strangest of European insects), builds a nest as small as that of the _Ameles_, although the insect itself is as large as the Praying Mantis. This nest is quite a small structure, composed of a small number of cells, arranged side by side in three or four series, sloping together at the neck. Here there is a complete absence of the porous envelope, although the nest is exposed to the weather, like the previous examples, affixed to some twig or fragment of rock. The lack of the insulating rind is a sign of different climatic conditions. The eggs of the _Empusa_ hatch shortly after they are laid, in warm and sunny weather. Not being exposed to the asperities of the winter, they need no protection other than the thin egg-cases themselves.

Are these nice and reasonable precautions, which rival the experiment of Rumford, a fortuitous result?--one of the innumerable combinations which fall from the urn of chance? If so, let us not recoil before the absurd: let us allow that the blindness of chance is gifted with marvellous foresight.

The Praying Mantis commences her nest at the blunter extremity, and completes it at the pointed tail. The latter is often prolonged in a sort of promontory, in which the insect expends the last drop of glutinous liquid as she stretches herself after her task. A sitting of two hours, more or less, without interruption, is required for the total accomplishment of the work. Directly the period of labour is over, the mother withdraws, indifferent henceforth to her completed task. I have watched her, half expecting to see her return, to discover some tenderness for the cradle of her family. But no: not a trace of maternal pleasure. The work is done, and concerns her no longer. Crickets approach; one of them even squats upon the nest. The Mantis takes no notice of them. They are peaceful intruders, to be sure; but even were they dangerous, did they threaten to rifle the nest, would she attack them and drive them away? Her impa.s.sive demeanour convinces me that she would not. What is the nest to her? She is no longer conscious of it.

I have spoken of the many embraces to which the Praying Mantis submits, and of the tragic end of the male, who is almost invariably devoured as though a lawful prey. In the s.p.a.ce of a fortnight I have known the same female to adventure upon matrimony no less than seven times. Each time the readily consoled widow devoured her mate. Such habits point to frequent laying; and we find the appearance confirmed, though not as a general rule. Some of my females gave me one nest only; others two, the second as capacious as the first. The most fruitful of all produced three; of these the two first were of normal dimensions, while the third was about half the usual size.

From this we can reckon the productivity of the insect's ovaries. From the transverse fissures of the median zone of the nest it is easy to estimate the layers of eggs; but these layers contain more or fewer eggs according to their position in the middle of the nest or near the ends.

The numbers contained by the widest and narrowest layers will give us an approximate average. I find that a nest of fair size contains about four hundred eggs. Thus the maker of the three nests, of which the last was half as large as the others, produced no less than a thousand eggs; eight hundred were deposited in the larger nests and two or three hundred in the smaller. Truly a fine family, but a thought ungainly, were it not that only a few of its members can survive.

Of a fair size, of curious structure, and well in evidence on its twig or stone, the nest of the Praying Mantis could hardly escape the attention of the Provencal peasant. It is well known in the country districts, where it goes by the name of _tigno_; it even enjoys a certain celebrity. But no one seems to be aware of its origin. It is always a surprise to my rustic neighbours when they learn that the well-known _tigno_ is the nest of the common Mantis, the _Prego-Dieu_.

This ignorance may well proceed from the nocturnal habits of the Mantis.

No one has caught the insect at work upon her nest in the silence of the night. The link between the artificer and the work is missing, although both are well known to the villager.

No matter: the singular object exists; it catches the eye, it attracts attention. It must therefore be good for something; it must possess virtue of some kind. So in all ages have the simple reasoned, in the childlike hope of finding in the unfamiliar an alleviation of their sorrows.

By general agreement the rural pharmacopoeia of Provence p.r.o.nounces the _tigno_ to be the best of remedies against chilblains. The method of employment is of the simplest. The nest is cut in two, squeezed and the affected part is rubbed with the cut surface as the juices flow from it. This specific, I am told, is sovereign. All sufferers from blue and swollen fingers should without fail, according to traditional usage, have recourse to the _tigno_.

Is it really efficacious? Despite the general belief, I venture to doubt it, after fruitless experiments on my own fingers and those of other members of my household during the winter of 1895, when the severe and persistent cold produced an abundant crop of chilblains. None of us, treated with the celebrated unguent, observed the swelling to diminish; none of us found that the pain and discomfort was in the least a.s.suaged by the sticky varnish formed by the juices of the crushed _tigno_. It is not easy to believe that others are more successful, but the popular renown of the specific survives in spite of all, probably thanks to a simple accident of ident.i.ty between the name of the remedy and that of the infirmity: the Provencal for "chilblain" is _tigno_. From the moment when the chilblain and the nest of the Mantis were known by the same name were not the virtues of the latter obvious? So are reputations created.

In my own village, and doubtless to some extent throughout the Midi, the _tigno_--the nest of the Mantis, not the chilblain--is also reputed as a marvellous cure for toothache. It is enough to carry it upon the person to be free of that lamentable affection. Women wise in such matters gather them beneath a propitious moon, and preserve them piously in some corner of the clothes-press or wardrobe. They sew them in the lining of the pocket, lest they should be pulled out with the handkerchief and lost; they will grant the loan of them to a neighbour tormented by some refractory molar. "Lend me thy _tigno_: I am suffering martyrdom!" begs the owner of a swollen face.--"Don't on any account lose it!" says the lender: "I haven't another, and we aren't at the right time of moon!"