THE MANTIS.—THE NEST

Social Life in the Insect World by Jean-Henri Fabre, is part of the HackerNoon Books Series. You can jump to any chapter in this book here. THE MANTIS.—THE NEST

CHAPTER VII. THE MANTIS.—THE NEST

Let us take a more pleasant aspect of the insect whose loves are so tragic. Its nest is a marvel. In scientific language it is known as the ootek, or the "egg-box." I shall not make use of this barbarous expression. As one does not speak of the "egg-box" of the titmouse, meaning "the nest of the titmouse," why should I invoke the box in speaking of the Mantis? It may look more scientific; but that does not interest me.

The nest of the Praying Mantis may be found almost everywhere in places exposed to the sun: on stones, wood, vine stocks, the twigs of bushes, stems of dried grass, and even on products of human industry, such as fragments of brick, rags of heavy cloth, and pieces of old boots. Any support will suffice, so long as it offers inequalities to which the base of the nest may adhere, and so provide a solid foundation. The usual dimensions of the nest are one and a half inches long by three-quarters of an inch wide, or a trifle larger. The colour is a pale tan, like that of a grain of wheat. Brought in contact with a flame the nest burns readily, and emits an odour like that of burning silk. The material of the nest is in fact a substance similar to silk, but instead of being drawn into a thread it is allowed to harden while a mass of spongy foam. If the nest is fixed on a branch the base creeps round it, envelops the neighbouring twigs, and assumes a variable shape according to the accidents of support; if it is fixed on a flat surface the under side, which is always moulded by the support, is itself flat. The nest then takes the form of a demi-ellipsoid, or, in other words, half an egg cut longitudinally; more or less obtuse at one end, but pointed at the other, and sometimes ending in a short curved tail.

In all cases the upper face is convex and regular. In it we can distinguish three well-marked and longitudinal zones. The middle zone, which is narrower than the others, is composed of thin plates arranged in couples, and overlapping like the tiles of a roof. The edges of these plates are free, leaving two parallel series of fissures by which the young can issue when the eggs are hatched. In a nest recently abandoned this zone is covered with fine cast-off skins which shiver at the least breath, and soon disappear when exposed to the open air. I will call this zone the zone of issue, as it is only along this bell that the young can escape, being set free by those that have preceded them.

In all other directions the cradle of this numerous family presents an unbroken wall. The two lateral zones, which occupy the greater part of the demi-ellipsoid, have a perfect continuity of surface. The little Mantes, which are very feeble when first hatched, could not possibly make their way through the tenacious substance of the walls. On the interior of these walls are a number of fine transverse furrows, signs of the various layers in which the mass of eggs is disposed.

Let us cut the nest in half transversely. We shall then see that the mass of eggs constitutes an elongated core, of very firm consistency, surrounded as to the bottom and sides by a thick porous rind, like solidified foam. Above the eggs are the curved plates, which are set very closely and have little freedom; their edges constituting the zone of issue, where they form a double series of small overlapping scales.

The eggs are set in a yellowish medium of horny appearance. They are arranged in layers, in lines forming arcs of a circle, with the cephalic extremities converging towards the zone of issue. This orientation tells us of the method of delivery. The newly-born larvæ will slip into the interval between two adjacent flaps or leaves, which form a prolongation of the core; they will then find a narrow passage, none too easy to effect, but sufficient, having regard to the curious provision which we shall deal with directly; they will then reach the zone of issue. There, under the overlapping scales, two passages of exit open for each layer of eggs. Half the larvæ will issue by the right-hand passage, half by that on the left hand. This process is repeated for each layer, from end to end of the nest.

Let us sum up those structural details, which are not easily grasped unless one has the nest before one. Lying along the axis of the nest, and in shape like a date-stone, is the mass of eggs, grouped in layers. A protective rind, a kind of solidified foam, envelops this core, except at the top, along the central line, where the porous rind is replaced by thin overlapping leaves. The free edges of these leaves form the exterior of the zone of issue; they overlap one another, forming two series of scales, leaving two exits, in the shape of narrow crevices, for each layer of eggs.

1. NEST OF THE PRAYING MANTIS.
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-glass, 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 impassively 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.

1. THE MANTIS DEVOURING THE MALE IN THE ACT OF MATING.
2. THE MANTIS COMPLETING HER NEST.
3. GOLDEN SCARABÆI CUTTING UP A LOB-WORM.

The foamy mass 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 mass. 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 homogeneous than that of the outer shell, 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, assures 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 mass, 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 masses of foam. On this fundamental foam, so to call it, which is soiled with earthy matters, we see here and there masses 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 larvæ 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 horny 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 mass 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 albumen to obtain a soufflée, 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 accumulated 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 mass 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 impassive 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 space 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 Provençal 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 Prègo-Diéu. 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 pharmacopœia of Provence pronounces 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 assuaged 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 identity between the name of the remedy and that of the infirmity: the Provençal 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!"

We will not laugh at the credulous victim; many a remedy triumphantly puffed on the latter pages of the newspapers and magazines is no more effectual. Moreover, this rural simplicity is surpassed by certain old books which form the tomb of the science of a past age. An English naturalist of the sixteenth century, the well-known physician, Thomas Moffat, informs us that children lost in the country would inquire their way of the Mantis. The insect consulted would extend a limb, indicating the direction to be taken, and, says the author, scarcely ever was the insect mistaken. This pretty story is told in Latin, with an adorable simplicity.

About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books.

This book is part of the public domain. Jean-Henri Fabre (2006). Social Life in the Insect World. Urbana, Illinois: Project Gutenberg. Retrieved October https://www.gutenberg.org/cache/epub/18350/pg18350-images.html

This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org, located at https://www.gutenberg.org/policy/license.html.