, 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, com