Fig. 2. A, the Garden Spider. B, diagram of a sector of the snare. f, foundation line; r, radius; v.s, viscid spiral; n.z, notched zone; h, hub.
The first business of the spider is to lay down the foundation lines. Any sort of trapezium—or even a triangle if large enough—in a more or less vertical plane will suffice, and under some circumstances the operation is simple enough. The spider attaches a line at the point of departure and crawls along, spinning as it goes and holding up the newly-spun thread by the claws of one of its hind feet, till it reaches a suitable spot for its farthest limit. It then hauls in the slack and makes it fast. It will probably return along the line thus laid down—still spinning—to the starting point, thus doubling the strength of the cable, and indeed a large spider will often repeat this operation several times. Now the upper boundary of the future web is secured. It is next necessary to find points of attachment for the lower boundary, and the spider either drops or climbs down—always carrying a line—from one of the ends of the upper line till it reaches a spot suitable for its purpose, and the previous performance is repeated. If there is any difficulty about a fourth attachment it is always open to the spider to climb back along the two lines already laid down, and by carrying a loose line with it, to secure at all events a triangular frame-work. This frame-work, whether trapezoid or triangular, will be reinforced several times and made thoroughly trustworthy before the work of making the actual snare is proceeded with.
Now the foregoing operation is obviously perfectly simple in certain cases, as, for instance when a spider has chosen lattice work, or the mouth of an empty barrel as its “pitch,” but snares may easily be found in situations where such a mode of procedure seems impossible. In a pine forest, for example, one may see huge webs stretched at a great height from the ground between boles ten feet apart; or one may find such a snare spread across a stream at a spot where the trees on either side do not intermingle their boughs. How in such cases does the spider accomplish its purpose?
There is little doubt that, wherever practicable, the spider walks round, sometimes crawling quite an astounding distance, but that it can at need, resort to another method, is easily proved by a very simple experiment in the house. Fill any vessel—a basin or a bath—with water and arrange an upright post in the middle, placing a spider upon it. If the air in the room is absolutely still the captive is powerless to escape, but if draughts are present it will sooner or later disappear; and it accomplishes this feat by emitting a thread which, caught by the air-current, is drawn out from its spinnerets till it by and by becomes entangled in the surrounding furniture. This power of emitting silk to some little distance and allowing the wind to draw it out is, as we shall see, frequently exercised in the early life of many spiders.
The foundation lines which may thus have given the spider great trouble to secure, are of extreme importance to it, and may serve for several snares in succession. There is little hesitation or delay about the subsequent operations. The spokes of the wheel are readily formed by carrying lines across to opposite points of the frame-work and uniting them where they intersect. They are laid down in no special order, but more or less alternation is generally noticeable—apparently for the purpose of keeping the tension equally balanced—and the spider will occasionally desist in order to go and brace up the frame-work with additional stays, which generally have the effect of converting it to a polygon.
Before long the requisite number of fairly equidistant “spokes” or radii are visible, and then the spider, starting from the centre, rapidly spins a spiral thread consisting of a few coils only, to the circumference, stepping from spoke to spoke. This is only a temporary scaffolding and will not be suffered to remain in the completed snare. If the structure is touched at this stage of the operations it does not adhere to the finger; the viscid spiral remains to be laid down. Though it does not hesitate for a moment, the spider now works with a peculiar deliberation, but the operation will be much better understood by actual observation than by any amount of description, and we shall only recommend the reader to note that the new spiral is exceedingly elastic and that at the moment of its attachment to a spoke it is stretched and let go like the string of a bow. The spider seems carefully to avoid treading on it as it proceeds, utilising the non-viscid spiral scaffolding already described.
