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.





THE GARDEN SPIDERS: THE QUESTION OF PROPERTY THE GLOW-WORM facebooktwittergoogle_plusredditpinterestlinkedinmail

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