THE SPIDER’S TELEGRAPH-WIRE
Of the six Garden Spiders I have noticed, two only, the Banded and the
Silky Spiders, stay 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, a hiding-place made of a few leaves held
together by stretched threads. It is here that they usually remain in
the daytime, motionless and sunk in meditation.
But the shrill light that vexes them is the joy of the fields. At
such time, the Locust hops more nimbly than ever, more gayly skims
the Dragon-fly. Besides, the sticky web, in spite of the rents
suffered during the night, is still in fairly good condition. If some
giddy-pated insect 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 does she know what
has happened? Let us explain the matter.
It is the vibration of the web which tells her, rather than the sight
of the captured object. To prove this, I laid upon several Spiders’
webs a dead Locust. I placed the Locust where the Spider might have
plainly seen it. Sometimes the Spider was in her web, and sometimes
she was outside, in her hiding-place. In both cases, nothing happened
at first. The Spider remained motionless, even when the Locust was at
a short distance in front of her. She did not seem to see the game at
all. Then, with a long straw, I set the dead insect trembling.
That was quite enough. The Banded Spider and the Silky Spider hastened
to the central floor, the others, who were in hiding, came down from
the branch; all went to the Locust, bound him with tape, treated him,
in short, as they would treat a live prey captured under the usual
conditions. It took the shaking of the web to decide them to attack.
If we look carefully behind the web of any Spider with a daytime
hiding-place, we shall see a thread that starts from the center of the
web and reaches the place where the Spider lurks. It is joined to the
web at the central point only. Its length is usually about twenty-two
inches, but the Angular Spider, settled high up in the trees, has shown
me some as long as eight or nine feet.
[Illustration: “The slanting cord is a telegraph wire.”]
This slanting line is a foot-bridge by which the Spider hurries to her
web when there is something going on there, and then, when her errand
is finished, returns to her hut. But that is not all it is. If it were,
the foot-bridge would be fastened to the upper end of the web. The
journey would then be shorter and the slope less steep.
The line starts from the center of the net because that is the place
where the spokes meet and therefore where the vibration from any part
of the net is best felt. Anything that moves upon the web sets it
shaking. All then that is needed is a thread going from this central
point to carry to a distance the news of a prey struggling in some part
or other of the net. The slanting cord is not only a foot-bridge: it is
a signaling-apparatus, a telegraph-wire.
In their youth, the Garden Spiders, who are then very wide-awake, know
nothing of the art of telegraphy. Only the old Spiders, meditating or
dozing in their green tent, are warned from afar, by telegraph, of what
takes place on the net.
To save herself from keeping a close watch that would be drudgery and
to remain alive to events even when resting, with her back turned on
the net, the hidden Spider always has her foot upon the telegraph-wire.
Here is a true story to prove it.
An Angular Spider 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 house, 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.
With her front half plunged into the back of her hut, the Spider
certainly cannot see her web; she could not even if she had good sight,
instead of being half blind as she is. 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 signaling-thread ends just at the tip of that leg. Whoever
has not seen the Spider in this attitude, with her hand, so to speak,
on the telegraph-receiver, knows nothing of one of the most curious
examples of animal cleverness. Let any game appear upon the scene,
and the slumberer, at once aroused by means of the leg receiving the
vibrations, hastens up. A Locust whom I myself lay on the web gives her
this agreeable shock, and what follows? If she is satisfied with her
prey, I am still more satisfied with what I have learned.
One word more. The web is often shaken by the wind. The signaling-cord
must pass this vibration to the Spider. Nevertheless, she does not
leave her hut and remains indifferent to the commotion prevailing in
the net. Her line, therefore, is something better than a bell-rope; 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 can tell the difference between the vibration
proceeding from a prisoner and the mere shaking caused by the wind.
[Illustration]