THE MANTIS: HER NEST

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CHAPTER VIII. THE MANTIS: HER NEST

Let us show the insect of the tragic amours under a more attractive aspect. Its nest is a marvel. In scientific language it is called ootheca, the egg-case. I shall not overwork this outlandish term. We do not say, “the Chaffinch’s egg-case,” when we mean, “the Chaffinch’s nest:” why should I be obliged to talk about a case when I speak of the Mantis? It may sound more learned; but that is not my business.

The nest of the Praying Mantis is found more or less everywhere in sunny places, on stones, wood, vine-stocks, twigs, dry grass and even on products of human industry, such as bits of brick, strips of coarse linen or the hard, shrivelled leather of an old boot. Any support serves, without distinction, so long as there is an uneven surface to which the bottom of the nest can be fixed, thus securing a solid foundation.

The usual dimensions are four centimetres in length and two in width.1 The colour is as golden as a grain of wheat. When set alight, the material burns readily and exhales a faint smell of singed silk. The substance is in fact akin to silk; only, instead of being drawn into thread, it has curdled into a frothy mass. When the nest is fixed to a branch, the base goes round the nearest twigs, envelops them and assumes a shape which varies in accordance with the support encountered; when it is fixed to a flat surface, the under side, which is always moulded on the support, is itself flat. The nest thereupon takes the form of a semi-ellipsoid, more or less blunt at one end, tapering at the other and often ending in a short, curved tail.

Whatever the support, the upper surface of the nest is systematically convex. We can distinguish in it three well-marked longitudinal zones. The middle one, which is narrower than the others, is composed of little plates or scales arranged in pairs and overlapping like the tiles of a roof. The edges of these plates are free, leaving two parallel rows of slits or fissures through [149]which the young emerge at hatching-time. In a recently-abandoned nest, this middle zone is furry with gossamer skins, discarded by the larvæ. These cast skins flutter at the least breath and soon vanish when exposed to rough weather. I will call it the exit-zone, because it is only along this median belt that the liberation of the young takes place, thanks to the outlets contrived beforehand.

In every other part the cradle of the numerous family presents an impenetrable wall. The two side zones, in fact, which occupy the greater part of the semi-ellipsoid, have perfect continuity of surface. The little Mantes, so feeble at the start, could never make their way out through so tough a substance. All that we see on it is a number of fine, transversal furrows, marking the various layers of which the mass of eggs consists.

Cut the nest across. It will now be perceived that the eggs, taken together, form an elongated kernel, very hard and firm and coated on the sides with a thick, porous rind, like solidified foam. Above are curved plates, set very closely and almost independent of one another; their edges end in [150]the exit-zone, where they form a double row of small, imbricated scales.

The eggs are buried in a yellow matrix of horny appearance. They are placed in layers, shaped like segments of a circle, with the ends containing the heads converging towards the exit-zone. This arrangement tells us how the deliverance is accomplished. The new-born larvæ will slip into the space left between two adjoining plates, a prolongation of the kernel, where they will find a narrow passage, difficult to go through, but just sufficient when we bear in mind the curious provision of which we shall speak presently; and by so doing they will reach the middle belt. Here, under the imbricated scales, two outlets open for each layer of eggs. Half of the larvæ undergoing their liberation will emerge through the right door, half through the left. And this is repeated for each layer from end to end of the nest.

To sum up these structural details, which are rather difficult to grasp for any one who has not the thing in front of him: lying along the axis of the nest and shaped like a date-stone is the cluster of eggs, grouped in layers. A protecting rind, a sort of solidified foam, surrounds this cluster, except at the top along [151]the median line, where the frothy rind is replaced by thin plates set side by side. The free ends of these plates form the exit-zone outside; they are imbricated in two series of scales and leave a couple of outlets, narrow clefts, for each layer of eggs.

The most striking part of my researches was being present at the construction of the nest and seeing how the Mantis goes to work to produce so complex a building. I managed it with some difficulty, for the laying takes place without warning and nearly always at night. After much useless waiting, chance at last favoured me. On the 5th of September, one of my boarders, who had been fertilized on the 29th of August, decided to lay her eggs before my eyes at about four o’clock in the afternoon.

Before watching her labour, let us note one thing: all the nests that I have obtained in the cages—and there are a good many of them—have as their support, with not a single exception, the wire gauze of the covers. I had taken care to place at the Mantes’ disposal a few rough bits of stone, a few tufts of thyme, foundations very often used in the open fields. My captives preferred the wire network, whose meshes furnish [152]a perfectly safe support as the soft material of the building becomes encrusted in them.

The nests, under natural conditions, enjoy no shelter; they have to endure the inclemencies of winter, to withstand rain, wind, frost and snow without coming loose. Therefore the mother always chooses an uneven support for the nest, so that the foundations can be wedged into it and a firm hold obtained. But, when circumstances permit, the better is preferred to the middling and the best to the better; and this must be the reason why the trelliswork of the cages is invariably adopted.

The only Mantis that I have been allowed to observe while engaged in laying does her work upside down, hanging from the top of the cage. My presence, my magnifying-glass, my investigations do not disturb her at all, so great is her absorption in her labour. I can raise the trellised dome, tilt it, turn it over, spin it this way and that, without the insect’s suspending its task for a moment. I can take my forceps and lift the long wings to see what is happening underneath. The Mantis takes no notice. Up to this point, all is well: the mother does not move and [153]impassively endures all the indiscretions of which I am guilty as an observer. And yet things do not go quite as I could wish, for the operation is too rapid and is too difficult to follow.

The end of the abdomen is immersed the whole time in a sea of foam, which prevents us from grasping the details of the process with any clearness. This foam is greyish-white, a little sticky and almost like soapsuds. When it first appears, it adheres slightly to a straw which I dip into it, but, two minutes afterwards, it is solidified and no longer sticks to the straw. In a very short time, its consistency is that which we find in an old nest.

The frothy mass consists mainly of air imprisoned in little bubbles. This air, which gives the nest a volume much greater than that of the Mantis’ belly, obviously does not come from the insect, though the foam appears at the entrance of the genital organs; it is taken from the atmosphere. The Mantis, therefore, builds above all with air, which is eminently suited to protect the nest against the weather. She discharges a sticky substance, similar to the caterpillars’ silk-fluid; and with this composition, which amalgamates [154]instantly with the outer air, she produces foam.

She whips her product just as we whip white of egg to make it rise and froth. The tip of the abdomen, opening with a long cleft, forms two lateral ladles which meet and separate with a constant, rapid movement, beating the sticky fluid and turning it into foam as it is discharged outside. In addition, between the two flapping ladles, we see the internal organs rising and falling, appearing and disappearing, after the manner of a piston-rod, without being able to distinguish their precise action, drowned as they are in the opaque stream of foam.

The end of the abdomen, ever throbbing, quickly opening and closing its valves, swings from right to left and left to right like a pendulum. The result of each swing is a layer of eggs inside and a transversal furrow outside. As the abdomen advances in the arc described, suddenly and at very close intervals it dips deeper into the foam, as though it were pushing something to the bottom of the frothy mass. Each time, no doubt, an egg is laid; but things happen so fast and under conditions so unfavourable to observation that I never once succeed in [155]seeing the ovipositor at work. I can judge of the arrival of the eggs only by the movements of the tip of the abdomen, which suddenly drives down and immerses itself more deeply.

At the same time, the viscous stuff is poured forth in intermittent waves and whipped and turned into foam by the two terminal valves. The froth obtained spreads over the sides of the layer of eggs and at the base, where I see it, pressed back by the abdomen, projecting through the meshes of the gauze. Thus the spongy covering is gradually brought into being as the ovaries are emptied.

I imagine, without being able to rely on direct observation, that for the central kernel, where the eggs are contained in a more homogeneous material than the rind, the Mantis employs her product as it is, without beating it up and making it foam. When the eggs are deposited, the two valves would produce foam to cover them. Once again, however, all this is very difficult to follow under the veil of the bubbling mass.

In a new nest, the exit-zone is coated with a layer of fine porous matter, of a pure, dull, almost chalky white, which contrasts with [156]the dirty white of the remainder of the nest. It is like the composition which confectioners make out of whipped white of egg, sugar and starch, with which to ornament their cakes. This snowy covering is very easily crumbled and removed. When it is gone, the exit-zone is clearly defined, with its two rows of plates with free edges. The weather, the wind and the rain sooner or later remove it in strips and flakes; and therefore the old nests retain no traces of it.

At the first inspection, one might be tempted to look upon this snowy matter as a different substance from the remainder of the nest. But can it be that the Mantis really employs two different products? By no means. Anatomy, to begin with, assures us of the unity of the materials. The organ that secretes the substance of the nest consists of twisted cylindrical tubes, divided into two sections of twenty each. All are filled with a colourless, viscous fluid, exactly similar in appearance wherever we look. There is nowhere any sign of a product with a chalky colouring.

The manner in which the snowy ribbon is formed also makes us reject the theory of different materials. We see the Mantis’ two [157]caudal threads sweeping the surface of the foamy mass, skimming, so to speak, the top of the froth, collecting it and retaining it along the back of the nest to form a band that looks like a ribbon of icing. What remains after this sweeping, or what trickles from the band before it sets, spreads over the sides in a thin wash of bubbles so fine that they cannot be seen without the magnifying-glass.

The surface of a muddy stream containing clay will be covered with coarse and dirty foam, churned up by the rushing torrent. On this foam, soiled with earthy materials, we see here and there masses of beautiful white froth, with smaller bubbles. Selection is due to the difference in density; and so the snow-white foam in places lies on top of the dirty foam whence it proceeds. Something similar happens when the Mantis builds her nest. The twin ladles reduce to foam the sticky spray from the glands. The thinnest and lightest portion, made whiter by its more delicate porousness, rises to the surface, where the caudal threads sweep it up and gather it into a snowy ribbon along the back of the nest.

Until now, with a little patience, observation [158]has been practicable and has given satisfactory results. It becomes impossible when we come to the very complex structure of that middle zone where exits are contrived for the emergence of the larvæ under the shelter of a double row of imbricated plates. The little that I am able to make out amounts to this: the tip of the abdomen, split wide from top to bottom, forms a sort of button-hole whose upper end remains almost fixed while the lower end, in swinging, produces foam and immerses eggs in it. It is that upper end which is undoubtedly responsible for the work of the middle zone. I always see it in the extension of that zone, in the midst of the fine white foam collected by the caudal filaments. These, one on the right, the other on the left, mark the boundaries of the band. They feel its edges; they seem to be testing the work. I can easily imagine them two long and exquisitely delicate fingers controlling the difficult business of construction.

But how are the two rows of scales obtained and the fissures, the exit-doors, which they shelter? I do not know. I cannot even guess. I leave the rest of the problem to others.[159]

What a wonderful mechanism is this which emits so methodically and swiftly the horny matrix of the central kernel, the protecting froth, the white foam of the median ribbon, the eggs and the fertilizing fluid and which at the same time is able to build overlapping plates, imbricated scales and alternating open fissures! We are lost in admiration. And yet how easily the work is done! The Mantis hangs motionless on the wire gauze which is the foundation of her nest. She gives not a glance at the edifice that is rising behind her; her legs are not called upon for assistance of any kind. The thing works of itself. We have here not an industrial task requiring the cunning of instinct; it is a purely automatic process, regulated by the insect’s tools and organization. The nest, with its highly complicated structure, proceeds solely from the play of the organs, even as in our own industries we manufacture by machinery a host of objects whose perfection would outwit our manual dexterity.

From another point of view, the Mantis’ nest is more remarkable still. We see in it a superb application of one of the most beautiful principles of physics, that of the conservation [160]of heat. The Mantis anticipated us in a knowledge of non-conducting bodies.

We owe to Rumford,2 the natural philosopher, the following curious experiment, which fittingly demonstrates the low conductivity of the air. The illustrious scientist dropped a frozen cheese into a mass of foam supplied by well-beaten eggs. The whole was subjected to the heat of an oven. The result in a short time was an omelette soufflée hot enough to burn the tongue, with the cheese in the middle as cold as at the beginning. The air contained in the bubbles of the surrounding froth explains the strange phenomenon. As an exceedingly poor thermal conductor, it had arrested the heat of the oven and prevented it from reaching the frozen substance in the centre.

Now what does the Mantis do? Precisely the same as Rumford: she whips her white of egg into an omelette soufflée, to protect the eggs collected into a central kernel. Her aim, it is true, is reversed: her coagulated foam is intended to ward off the cold, not the heat. But a protection against [161]one is a protection against the other; and the ingenious physicist, had he wished, could easily with the same frothy wrapper have maintained the heat of a body in cold surroundings.

Rumford knew the secrets of the stratum of air thanks to the accumulated knowledge of his ancestors, his own researches and his own studies. How is it that for no one knows how many centuries the Mantis has beaten our natural philosophers in the matter of this delicate problem of heat? How did she come to think of wrapping a blanket of foam around her mass of eggs, which, fixed without any shelter to a twig or stone, has to endure the rigours of winter with impunity?

The other Mantidæ of my neighbourhood, the only ones of whom I can speak with full knowledge, use the non-conducting wrapper of solidified foam or do without it, according as the eggs are destined to live through the winter or not. The little Grey Mantis, who differs so greatly from the other owing to the almost entire absence of wings in the female, builds a nest not quite so big as a cherry-stone and covers it very cleverly with a rind of froth. Why this beaten-up envelope? [162]Because the nest of the Grey Mantis, like that of the Praying Mantis, has to last through the winter, exposed on its bough or stone to all the dangers of the bad weather.

On the other hand, in spite of her size, which is equal to that of the Praying Mantis, Empusa pauperata, who is the most curious of our insects, builds a nest as small as that of the Grey Mantis. It is a very modest edifice, consisting of a small number of cells set side by side in three or four rows joined together. Here there is no frothy envelope at all, though the nest, like those mentioned above, is fixed in an exposed situation on some twig or broken stone. This absence of a non-conducting mattress points to a difference in climatic conditions. The Empusa’s eggs, in fact, hatch soon after they are laid, during the fine weather. Not having to undergo the inclemencies of winter, they have no protection but the slender sheath of their cases.

Are these scrupulous and rational precautions, which rival Rumford’s omelette soufflée, a casual result, one of those numberless combinations turned out by the wheel of fortune? If so, let us not shrink from any absurdity, but recognize straightway that the [163]blindness of chance is endowed with marvellous foresight.

The blunt end of the nest is the first part built by the Praying Mantis and the tapering end the last. The latter is often prolonged into a sort of spur made by drawing out the final drop of albuminous fluid used. To complete the whole thing demands about two hours of concentrated work, free from interruption.

As soon as the laying is finished, the mother withdraws, callously. I expected to see her return and display some tender feeling for the cradle of her family. But there is not the least sign of maternal joy. The work is done and possesses no further interest for her. Some Locusts have come up. One even perches on the nest. The Mantis pays no attention to the intruders. They are peaceful, it is true. Would she drive them away if they were dangerous and if they looked like ripping open the egg-casket? Her impassive behaviour answers no. What is the nest to her henceforth? She knows it no more.

I have spoken of the repeated coupling of the Praying Mantis and of the tragic end of the male, who is nearly always devoured like [164]an ordinary piece of game. In the space of a fortnight I have seen the same female marry again as many as seven times over. Each time the easily-consoled widow ate up her mate. Such habits make one assume repeated layings; and these do, in fact, take place, though they are not the general rule. Among my mothers, some gave me only one nest; others supplied me with two, both equally large. The most fertile produced three, of which the first two were of normal size, while the third was reduced to half the usual dimensions.

The last-mentioned insect shall tell us the population which the Mantis’ ovaries are capable of producing. Reckoning by the transversal furrows of the nest, we can easily count the layers of eggs. These are more or less rich according to their position at the middle of the ellipsoid or at the ends. The numbers of the eggs in the biggest and in the smallest layer furnish an average from which we can approximately deduce the total. In this way I find that a good-sized nest contains about four hundred eggs. The mother with the three nests, the last of which was only half the size of the others, therefore left as her offspring no fewer than a thousand [165]germs; those who laid twice left eight hundred; and the less fertile mothers three to four hundred. In every case, it is a fine family, which would even become cumbrous, if it were not subjected to drastic pruning.

The pretty little Grey Mantis is much less lavish. In my cages she lays only once; and her nest contains some sixty eggs at most. Although built on the same principles and likewise fixed in the open, it differs remarkably from the work of the Praying Mantis, first in its scanty dimensions and next in certain details of structure. It is shaped like a shelving ridge. The two sides are curved and the median line projects into a slightly denticulated crest. It is grooved crosswise by about a dozen furrows, corresponding with the several layers of eggs. Here we find no exit-zone, with short, imbricated scales; no snowy ribbon with alternating outlets. The whole surface, including the foundation, is uniformly covered with a shiny red-brown rind, in which the bubbles are very small. One end is ogival in shape; the other, the end where the nest finishes, is abruptly truncated and is prolonged above in a short spur. The whole forms a kernel surrounded by the foamy rind. Like the Praying [166]Mantis, the Grey Mantis works at night, an unfortunate circumstance for the observer.

Large in size, curious in build and moreover plainly visible on its stone or its bit of brushwood, the Praying Mantis’ nest could not fail to attract the attention of the Provençal peasant. It is, in fact, very well-known in the country districts, where it bears the name of tigno; it even enjoys a great reputation. Yet nobody seems to be aware of its origin. It is always a matter for surprise to my rustic neighbours when I inform them that the famous tigno is the nest of the common Prègo-Diéu. Their ignorance might well be due to the Mantis’ habit of laying her eggs at night. The insect has never been caught working at her nest in the mysterious darkness; and the link between the worker and the work is missing, though both are known to every one in the village.

No matter: the singular object exists; it attracts the eye, it captivates the attention. It must therefore be good for something, it must possess virtues. Thus, throughout the ages, have the ingenuous argued, hoping to find in the unfamiliar an alleviation of their pains.

By general consent, the rural pharmacopœia, [167]in Provence, extols the tigno as the best remedy against chilblains. The way to employ it is exceedingly simple. You cut the thing in two, squeeze it and rub the afflicted part with the streaming juice. The remedy, they say, works like a charm. Every one mad with the itching of blue and swollen fingers hastens to have recourse to the tigno, according to traditional custom. Does he really obtain relief?

Notwithstanding the unanimous conviction, I venture to doubt it, after the fruitless experiments tried upon myself and other members of my household during the winter of 1895, when the long and severe frost produced any amount of epidermic discomfort. Not one of us, when smeared with the celebrated ointment, saw the chilblains on his fingers decrease nor felt the irritation relieved in the slightest degree by the albuminous varnish of the crushed tigno. It seems probable that others are no more successful and that the popular reputation of the specific nevertheless survives, probably because of a mere identity of name between the remedy and the disease: the Provençal for chilblain is tigno. Once that the nest of the Praying Mantis and the chilblain are [168]known by the same name, do not the virtues of the former become obvious? That is how reputations are created.

In my village and no doubt for some distance around, the tigno—I am now speaking of the Mantis’ nest—is also highly praised as a wonderful cure for toothache. As long as you have it on you, you need never fear that trouble. Our housewives gather it under a favourable moon; they preserve it religiously in a corner of the press; they sew it into their pocket, lest they should lose it when taking out their handkerchief; and neighbours borrow it when tortured by some molar.

“Lend me your tigno: I am in agony,” says the sufferer with the swollen face.

The other hastens to unstitch and to hand over the precious object:

“Don’t lose it, whatever you do,” she impresses on her friend. “It’s the only one I have; and this isn’t the right time of moon.”

Let us not laugh at this eccentric toothache-nostrum: many remedies that sprawl triumphantly over the back pages of the newspapers are no more effective. Besides, this rural simplicity is surpassed by some old books in which slumbers the [169]science of by-gone days. An English naturalist of the sixteenth century, Thomas Moffett, the physician,3 tells us that, if a child lose his way in the country, he will ask the Mantis to put him on his road. The Mantis, adds the author, “will stretch out one of her feet and shew him the right way and seldome or never misse.” These charming things are told with adorable simplicity:

“Tam divina censetur bestiola, ut puero interroganti de via, extento digito rectam monstrat atque raro vel nunquam fallat.”

Where did the credulous scholar get this pretty story? Not in England, where the Mantis cannot live; not in Provence, where we find no trace of the boyish question. All said, I prefer the spiflicating virtues of the tigno to the old naturalist’s imaginings.

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