THE CIRCULAR SNARE

Select the most perfect circular snare at hand, and examine it attentively. In the autumn, when the large garden-spider, Epeira diademata (fig. 2 A), is mature, it will probably be easy to find such a snare a foot or more in diameter. It is stretched within an irregular frame of foundation lines of extra thickness and strength, and consists of a large number of radii or spokes connected by what appear to be a series of concentric circles, in reality a continuous spiral, like the hair-spring of a watch. The central portion is different from the rest of the wheel. Probably in the very centre there is a vacant space and round this a hub, consisting of a spiral line different in appearance from that of the main spiral. It does not leave a radius exactly at the point where it strikes it, and the rather zig-zag effect has caused it to be known as the “notched zone.” Touch the web and it adheres to the finger, but all its lines are not adhesive. Test this with some fine-pointed implement, and the foundation lines, the radii and the notched zone will give negative results; the spiral line alone is viscid, and its viscidity is due to the presence of thousands of little beads of gummy matter strung on a thin elastic thread. The vast number and uniformity of these beads—estimated at 120,000 on a large web—excited the wonder and admiration of naturalists until it was proved that they were not deposited by the spider as beads at all, but as a uniform coating of viscid matter which subsequently arranged itself into equidistant globules easily explicable by the physicist. Indeed precisely the same phenomenon is seen on a dew-laden web, where similar but very much larger beads of water decorate all the lines.

From the hub of the wheel we shall very likely notice a rather stout cable diverging from the plane of the snare and leading to a nest of leaves spun together. Here the spider is to be found when not on duty in the centre of the wheel, and here it constructs its egg-cocoons.

This, then, is the complete circular snare, but we shall understand it much better if we watch the spider at work in its construction.

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 [Pg 15]
[Pg 16]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.

A little attention to the centre of the wheel, and the snare is complete. Some species of Epeira entirely remove the centre, leaving a circular empty space, while others fill it with an irregular network of threads.

How does the garden spider avoid getting caught in its own web? We have shown that there are many lines which are not viscid, and no doubt these are utilised as far as possible, but it can hardly happen that the spider never touches adhesive portions of the web with legs or body.

Possibly some explanation is furnished by an ingenious experiment which Fabre performed. He found that a glass rod, lightly smeared with oil, did not adhere to the viscid spiral; neither did a leg freshly taken from a garden-spider unless allowed to remain in contact for a considerable time. When, however, this leg had been washed with bisulphide of carbon, which dissolves any kind of oily substance, it adhered at once. It would seem likely, therefore, that the legs and body of the spider itself are protected by some oily exudation from any danger of adherence to its own lines.