In twenty-four hours, the threads have lost their contents and are reduced to almost invisible streaks. If I then lay a drop of water on the glass, I get a sticky solution, similar to that which a particle of gum arabic might yield. The conclusion is evident: the Epeira’s glue is a substance that absorbs moisture freely. In an atmosphere with a high degree of humidity, it becomes saturated and percolates by sweating through the side of the tubular threads.
These data explain certain facts relating to the work of the net. The full-grown Banded and Silky Epeirae weave at very early hours, long before dawn. Should the air turn misty, they sometimes leave that part of the task unfinished: they build the general framework, they lay the spokes, they even draw the auxiliary spiral, for all these parts are unaffected by excess of moisture; but they are very careful not to work at the lime-threads, which, if soaked by the fog, would dissolve into sticky shreds and lose their efficacy by being wetted. The net that was started will be finished to-morrow, if the atmosphere be favourable.
While the highly-absorbent character of the snaring-thread has its drawbacks, it also has compensating advantages. Both Epeirae, when hunting by day, affect those hot places, exposed to the fierce rays of the sun, wherein the Crickets delight. In the torrid heats of the dog-days, therefore, the lime-threads, but for special provisions, would be liable to dry up, to shrivel into stiff and lifeless filaments. But the very opposite happens. At the most scorching times of the day, they continue supple, elastic and more and more adhesive.
How is this brought about? By their very powers of absorption. The moisture of which the air is never deprived penetrates them slowly; it dilutes the thick contents of their tubes to the requisite degree and causes it to ooze through, as and when the earlier stickiness decreases. What bird-catcher could vie with the Garden Spider in the art of laying lime-snares? And all this industry and cunning for the capture of a Moth!
Then, too, what a passion for production! Knowing the diameter of the orb and the number of coils, we can easily calculate the total length of the sticky spiral. We find that, in one sitting, each time that she remakes her web, the Angular Epeira produces some twenty yards of gummy thread. The more skilful Silky Epeira produces thirty. Well, during two months, the Angular Epeira, my neighbour, renewed her snare nearly every evening. During that period, she manufactured something like three-quarters of a mile of this tubular thread, rolled into a tight twist and bulging with glue.
I should like an anatomist endowed with better implements than mine and with less tired eyesight to explain to us the work of the marvellous rope-yard. How is the silky matter moulded into a capillary tube? How is this tube filled with glue and tightly twisted? And how does this same wire-mill also turn out plain threads, wrought first into a framework and then into muslin and satin; next, a russet foam, such as fills the wallet of the Banded Epeira; next, the black stripes stretched in meridian curves on that same wallet? What a number of products to come from that curious factory, a Spider’s belly! I behold the results, but fail to understand the working of the machine. I leave the problem to the masters of the microtome and the scalpel.
CHAPTER XII: 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.