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.
[33] 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 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 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 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 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 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 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 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 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 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 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.
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 of heat. The Mantis
anticipated us in a knowledge of non-conducting bodies.
We owe to Rumford, [34] 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 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?
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 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 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 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 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, 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
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 science of by-gone days. An English
naturalist of the sixteenth century, Thomas Moffett, the physician,
[35] 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.