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THE GARDEN SPIDERS: THE TELEGRAPH-WIRE




Of the six Garden Spiders that form the object of my observations, two
only, the Banded and the silky Epeira, remain constantly in their webs,
even under the blinding rays of a fierce sun. The others, as a rule, do
not show themselves until nightfall. At some distance from the net, they
have a rough and ready retreat in the brambles, an ambush made of a few
leaves held together by stretched threads. It is here that, for the most
part, they remain in the daytime, motionless and sunk in meditation.

But the shrill light that vexes them is the joy of the fields. At such
times, the Locust hops more nimbly than ever, more gaily skims the Dragon-
fly. Besides, the limy web, despite the rents suffered during the night,
is still in serviceable condition. If some giddy-pate allow himself to
be caught, will the Spider, at the distance whereto she has retired, be
unable to take advantage of the windfall? Never fear. She arrives in a
flash. How is she apprised? Let us explain the matter.

The alarm is given by the vibration of the web, much more than by the
sight of the captured object. A very simple experiment will prove this.
I lay upon a Banded Epeira's lime-threads a Locust that second
asphyxiated with carbon disulphide. The carcass is placed in front, or
behind, or at either side of the Spider, who sits moveless in the centre
of the net. If the test is to be applied to a species with a daytime
hiding-place amid the foliage, the dead Locust is laid on the web, more
or less near the centre, no matter how.

In both cases, nothing happens at first. The Epeira remains in her
motionless attitude, even when the morsel is at a short distance in front
of her. She is indifferent to the presence of the game, does not seem to
perceive it, so much so that she ends by wearing out my patience. Then,
with a long straw, which enables me to conceal myself slightly, I set the
dead insect trembling.

That is quite enough. The Banded Epeira and the Silky Epeira hasten to
the central floor; the others come down from the branch; all go to the
Locust, swathe him with tape, treat him, in short, as they would treat a
live prey captured under normal conditions. It took the shaking of the
web to decide them to attack.

Perhaps the grey colour of the Locust is not sufficiently conspicuous to
attract attention by itself. Then let us try red, the brightest colour
to our retina and probably also to the Spiders'. None of the game hunted
by the Epeirae being clad in scarlet, I make a small bundle out of red
wool, a bait of the size of a Locust. I glue it to the web.

My stratagem succeeds. As long as the parcel is stationary, the Spider
is not roused; but, the moment it trembles, stirred by my straw, she runs
up eagerly.

There are silly ones who just touch the thing with their legs and,
without further enquiries, swathe it in silk after the manner of the
usual game. They even go so far as to dig their fangs into the bait,
following the rule of the preliminary poisoning. Then and then only the
mistake is recognized and the tricked Spider retires and does not come
back, unless it be long afterwards, when she flings the cumbersome object
out of the web.

There are also clever ones. Like the others, these hasten to the red-
woollen lure, which my straw insidiously keeps moving; they come from
their tent among the leaves as readily as from the centre of the web;
they explore it with their palpi and their legs; but, soon perceiving
that the thing is valueless, they are careful not to spend their silk on
useless bonds. My quivering bait does not deceive them. It is flung out
after a brief inspection.

Still, the clever ones, like the silly ones, run even from a distance,
from their leafy ambush. How do they know? Certainly not by sight.
Before recognizing their mistake, they have to hold the object between
their legs and even to nibble at it a little. They are extremely short-
sighted. At a hand's-breadth's distance, the lifeless prey, unable to
shake the web, remains unperceived. Besides, in many cases, the hunting
takes place in the dense darkness of the night, when sight, even if it
were good, would not avail.

If the eyes are insufficient guides, even close at hand, how will it be
when the prey has to be spied from afar! In that case, an intelligence-
apparatus for long-distance work becomes indispensable. We have no
difficulty in detecting the apparatus.

Let us look attentively behind the web of any Epeira with a daytime
hiding-place: we shall see a thread that starts from the centre of the
network, ascends in a slanting line outside the plane of the web and ends
at the ambush where the Spider lurks all day. Except at the central
point, there is no connection between this thread and the rest of the
work, no interweaving with the scaffolding-threads. Free of impediment,
the line runs straight from the centre of the net to the ambush-tent. Its
length averages twenty-two inches. The Angular Epeira, settled high up
in the trees, has shown me some as long as eight or nine feet.

There is no doubt that this slanting line is a foot-bridge which allows
the Spider to repair hurriedly to the web, when summoned by urgent
business, and then, when her round is finished, to return to her hut. In
fact, it is the road which I see her follow, in going and coming. But is
that all? No; for, if the Epeira had no aim in view but a means of rapid
transit between her tent and the net, the foot-bridge would be fastened
to the upper edge of the web. The journey would be shorter and the slope
less steep.

Why, moreover, does this line always start in the centre of the sticky
network and nowhere else? Because that is the point where the spokes
meet and, therefore, the common centre of vibration. Anything that moves
upon the web sets it shaking. All then that is needed is a thread
issuing from this central point to convey to a distance the news of a
prey struggling in some part or other of the net. The slanting cord,
extending outside the plane of the web, is more than a foot-bridge: it
is, above all, a signalling-apparatus, a telegraph-wire.

Let us try experiment. I place a Locust on the network. Caught in the
sticky toils, he plunges about. Forthwith, the Spider issues impetuously
from her hut, comes down the foot-bridge, makes a rush for the Locust,
wraps him up and operates on him according to rule. Soon after, she
hoists him, fastened by a line to her spinneret, and drags him to her
hiding-place, where a long banquet will be held. So far, nothing new:
things happen as usual.

I leave the Spider to mind her own affairs for some days, before I
interfere with her. I again propose to give her a Locust; but, this
time, I first cut the signalling-thread with a touch of the scissors,
without shaking any part of the edifice. The game is then laid on the
web. Complete success: the entangled insect struggles, sets the net
quivering; the Spider, on her side, does not stir, as though heedless of
events.

The idea might occur to one that, in this business, the Epeira stays
motionless in her cabin since she is prevented from hurrying down,
because the foot-bridge is broken. Let us undeceive ourselves: for one
road open to her there are a hundred, all ready to bring her to the place
where her presence is now required. The network is fastened to the
branches by a host of lines, all of them very easy to cross. Well, the
Epeira embarks upon none of them, but remains moveless and self-absorbed.

Why? Because her telegraph, being out of order, no longer tells her of
the shaking of the web. The captured prey is too far off for her to see
it; she is all unwitting. A good hour passes, with the Locust still
kicking, the Spider impassive, myself watching. Nevertheless, in the
end, the Epeira wakes up: no longer feeling the signalling-thread, broken
by my scissors, as taut as usual under her legs, she comes to look into
the state of things. The web is reached, without the least difficulty,
by one of the lines of the framework, the first that offers. The Locust
is then perceived and forthwith enswathed, after which the signalling-
thread is remade, taking the place of the one which I have broken. Along
this road the Spider goes home, dragging her prey behind her.

My neighbour, the mighty Angular Epeira, with her telegraph-wire nine
feet long, has even better things in store for me. One morning, I find
her web, which is now deserted, almost intact, a proof that the night's
hunting has not been good. The animal must be hungry. With a piece of
game for a bait, I hope to bring her down from her lofty retreat.

I entangle in the web a rare morsel, a Dragon-fly, who struggles
desperately and sets the whole net a-shaking. The other, up above,
leaves her lurking-place amid the cypress-foliage, strides swiftly down
along her telegraph-wire, comes to the Dragon-fly, trusses her and at
once climbs home again by the same road, with her prize dangling at her
heels by a thread. The final sacrifice will take place in the quiet of
the leafy sanctuary.

A few days later, I renew my experiment under the same conditions, but,
this time, I first cut the signalling-thread. In vain I select a large
Dragon-fly, a very restless prisoner; in vain I exert my patience: the
Spider does not come down all day. Her telegraph being broken, she
receives no notice of what is happening nine feet below. The entangled
morsel remains where it lies, not despised, but unknown. At nightfall,
the Epeira leaves her cabin, passes over the ruins of her web, finds the
Dragon-fly and eats her on the spot, after which the net is renewed.

One of the Epeirae whom I have had the opportunity of examining
simplifies the system, while retaining the essential mechanism of a
transmission-thread. This is the Crater Epeira (_Epeira cratera_,
WALCK.), a species seen in spring, at which time she indulges especially
in the chase of the Domestic Bee, upon the flowering rosemaries. At the
leafy end of a branch, she builds a sort of silken shell, the shape and
size of an acorn-cup. This is where she sits, with her paunch contained
in the round cavity and her forelegs resting on the ledge, ready to leap.
The lazy creature loves this position and rarely stations herself head
downwards on the web, as do the others. Cosily ensconced in the hollow
of her cup, she awaits the approaching game.

Her web, which is vertical, as is the rule among the Epeirae, is of a
fair size and always very near the bowl wherein the Spider takes her
ease. Moreover, it touches the bowl by means of an angular extension;
and the angle always contains one spoke which the Epeira, seated, so to
speak, in her crater, has constantly under her legs. This spoke,
springing from the common focus of the vibrations from all parts of the
network, is eminently fitted to keep the Spider informed of whatsoever
happens. It has a double office: it forms part of the Catherine-wheel
supporting the lime-threads and it warns the Epeira by its vibrations. A
special thread is here superfluous.

The other snarers, on the contrary, who occupy a distant retreat by day,
cannot do without a private wire that keeps them in permanent
communication with the deserted web. All of them have one, in point of
fact, but only when age comes, age prone to rest and to long slumbers. In
their youth, the Epeirae, who are then very wide-awake, know nothing of
the art of telegraphy. Besides, their web, a short-lived work whereof
hardly a trace remains on the morrow, does not allow of this kind of
industry. It is no use going to the expense of a signalling-apparatus
for a ruined snare wherein nothing can now be caught. Only the old
Spiders, meditating or dozing in their green tent, are warned from afar,
by telegraph, of what takes place on the web.

To save herself from keeping a close watch that would degenerate into
drudgery and to remain alive to events even when resting, with her back
turned on the net, the ambushed Spider always has her foot upon the
telegraph-wire. Of my observations on this subject, let me relate the
following, which will be sufficient for our purpose.

An Angular Epeira, with a remarkably fine belly, has spun her web between
two laurestine-shrubs, covering a width of nearly a yard. The sun beats
upon the snare, which is abandoned long before dawn. The Spider is in
her day manor, a resort easily discovered by following the
telegraph-wire. It is a vaulted chamber of dead leaves, joined together
with a few bits of silk. The refuge is deep: the Spider disappears in it
entirely, all but her rounded hind-quarters, which bar the entrance to
the donjon.

With her front half plunged into the back of her hut, the Epeira
certainly cannot see her web. Even if she had good sight, instead of
being purblind, her position could not possibly allow her to keep the
prey in view. Does she give up hunting during this period, of bright
sunlight? Not at all. Look again.

Wonderful! One of her hind-legs is stretched outside the leafy cabin;
and the signalling-thread ends just at the tip of that leg. Whoso has
not seen the Epeira in this attitude, with her hand, so to speak, on the
telegraph-receiver, knows nothing of one of the most curious instances of
animal cleverness. Let any game appear upon the scene; and the
slumberer, forthwith aroused by means of the leg receiving the
vibrations, hastens up. A Locust whom I myself lay on the web procures
her this agreeable shock and what follows. If she is satisfied with her
bag, I am still more satisfied with what I have learnt.

The occasion is too good not to find out, under better conditions as
regards approach, what the inhabitant of the cypress-trees has already
shown me. The next morning, I cut the telegraph-wire, this time as long
as one's arm and held, like yesterday, by one of the hind-legs stretched
outside the cabin. I then place on the web a double prey, a Dragon-fly
and a Locust. The latter kicks out with his long, spurred shanks; the
other flutters her wings. The web is tossed about to such an extent that
a number of leaves, just beside the Epeira's nest, move, shaken by the
threads of the framework affixed to them.

And this vibration, though so close at hand, does not rouse the Spider in
the least, does not make her even turn round to enquire what is going on.
The moment that her signalling-thread ceases to work, she knows nothing
of passing events. All day long, she remains without stirring. In the
evening, at eight o'clock, she sallies forth to weave the new web and at
last finds the rich windfall whereof she was hitherto unaware.

One word more. The web is often shaken by the wind. The different parts
of the framework, tossed and teased by the eddying air-currents, cannot
fail to transmit their vibration to the signalling-thread. Nevertheless,
the Spider does not quit her hut and remains indifferent to the commotion
prevailing in the net. Her line, therefore, is something better than a
bell-rope that pulls and communicates the impulse given: it is a
telephone capable, like our own, of transmitting infinitesimal waves of
sound. Clutching her telephone-wire with a toe, the Spider listens with
her leg; she perceives the innermost vibrations; she distinguishes
between the vibration proceeding from a prisoner and the mere shaking
caused by the wind.





Next: THE GARDEN SPIDERS: PAIRING AND HUNTING

Previous: THE GARDEN SPIDERS: THE LIME-SNARE



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