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Insect Adventures

<h2 id="chapter-24"><ANTIMG src="images/i_266.jpg" alt="" /> CHAPTER XXIV THE BUILDING OF A SPIDER’S WEB</h2> The smallest garden contains the Garden Spiders, all clever weavers. Let us go every evening, step by step, from one border of tall rosemaries to the next. Should things move too slowly, we will sit down at the foot of the shrubs, where the light falls favorably, and watch with unwearying attention. Let us give ourselves a title, “Inspector of Spiders’ Webs!” There are not many people in that profession, and we shan’t make any money by it; but never mind, we shall learn some very interesting things. The Spiders I watch are young ones, much slenderer than they will be in the late autumn. They work by day, work even in the sun, whereas the old ones weave only at night. Work starts in July, a couple of hours before sunset. The spinstresses of my inclosures then leave their daytime hiding-places, choose their posts and begin to spin, one here, another there. There are many of them; we can choose where we please. Let us stop in front of this one, whom we surprise in the act of laying the foundations of her web. She runs about the rosemary hedge, from the tip of one branch to another, within the limits of some eighteen inches. Gradually, she puts a thread in position, drawing it from her body with the combs attached to her hind-legs. She comes and goes impetuously, as though at random; she goes up, comes down, goes up again, dives down again and each time strengthens the points of contact with threads distributed here and there. The result is a sort of frame. The shapeless structure is what she wishes; it marks out a flat, free, and perpendicular space. This is all that is necessary. A special thread, the foundation of the stronger net which will be built later, is stretched across the area of the other. It can be told from the others by its isolation, its position at a distance from any twig that might interfere with its swaying length. It never fails to have, in the middle, a thick white point, formed of a little silk cushion. The time has come to weave the hunting-snare. The Spider starts from the center, which bears the white signpost, and, running along the cross-thread, hurriedly reaches the circumference, that is to say, the irregular frame inclosing the free space. Still with the same sudden movement, she rushes from the outside to the center; she starts again backwards and forwards, makes for the right, the left, the top, the bottom; she hoists herself up, dives down, climbs up again, runs down and always returns to the central landmark by roads that slant in the most unexpected manner. Each time a radius or spoke is laid, here, there, or elsewhere, in what looks like mad disorder. <div class="figcenter"> <ANTIMG src="images/i_268.jpg" alt="the finished web, so neat and regular in appearance" /></div> Any one looking at the finished web, so neat and regular in appearance, would think that the Spider laid the spokes in an orderly fashion, one after the other. She does nothing of the sort, but she knows what she is about, all the same. After setting a few spokes in one direction, the Spider runs across to the other side to draw some in the opposite direction. These sudden changes have a reason; they show us how clever the Spider is in her business. If she began by laying all the spokes on one side, she would pull the web out of shape or even destroy it. She must put some on the other side to balance. She is a past mistress of the secrets of rope-building, without serving an apprenticeship. One would think that this interrupted and apparently disordered labor must result in a confused piece of work. Wrong: the rays are equidistant and form a beautifully regular circle. Their number is a characteristic mark of the different species. The Angular Epeira places twenty-one in her web, the Banded Epeira thirty-two, the Silky Epeira forty-two. These numbers are not absolutely fixed; but the variation is very slight. Now which of us would undertake, offhand, without much preliminary experiment and without measuring-instruments, to divide a circle into a given quantity of sectors or parts of equal width? The Garden Spider, though weighted with a wallet and tottering on threads shaken by the wind, performs the delicate division without stopping to think. She achieves it by a method which seems mad according to our notions of geometry. Out of disorder she brings order. We are amazed at the result obtained. How does this Spider come to succeed with her difficult problem, so strangely managed? I am still asking myself the question. The laying of the radii or spokes is finished. The Spider takes her place in the center, on the little cushion. Stationed on this support, she slowly turns round and round. She is engaged on a delicate piece of work. With an extremely thin thread, she describes from spoke to spoke, starting from the center, a spiral line with very close coils. This is the center of the web. I will call it the “resting-floor.” The thread now becomes thicker. The first could hardly be seen; the second is plainly visible. The Spider shifts her position with great slanting strides, turns a few times, moving farther and farther from the center, fixes her line each time to the spoke which she crosses, and at last comes to a stop at the lower edge of the frame. She has described a spiral with coils of rapidly-increasing width. The average distance between the coils, even in the webs of the young Spiders, is about one third of an inch. This spiral is not a curved line. All curves are banished from the Spiders’ work; nothing is used but the straight line and its combinations. This line forms the cross-bars, or supporting rungs, connecting the spokes, or radii. All this is but a support for the snaring-web. Clinging on the one hand to the radii, on the other to the cross-bars, the Spider covers the same ground as when laying the first spiral, but in the opposite direction: formerly, she moved away from the center; now she moves towards it and with closer and more numerous circles. She starts from the end of the first spiral, near the outside of the web. What follows is hard to observe, for the movements are very quick and jerky, consisting of a series of sudden little rushes, sways, and bends that bewilder the eye. The two hind-legs, the weaving implements, keep going constantly. One draws out the thread from the spinneret, and passes it to the other, which lays it on the radius. As soon as the radius is touched, the thread sticks to it by its own glue. <div class="figcenter"> <ANTIMG src="images/i_271.jpg" alt="[They] sign their work by laying a broad white ribbon in a thick zigzag from the center to the lower edge of the web" /></div> The Spider, without a stop of any kind, turns and turns and turns, drawing nearer to the center and always fixing her thread at each spoke which she crosses. At last, at some distance from the center, on the edge of what I have called the resting-floor, the Spider suddenly ends her spiral. She next eats the little cushion in the center, which is a mat of ends of saved silk. She does this to economize silk, for after she has eaten it the cushion will be turned into silk for the next web she spins. Two Spiders, the Banded and the Silky, sign their work by laying a broad white ribbon in a thick zigzag from the center to the lower edge of the web. Sometimes they put a second band of the same shape, but a little shorter, opposite the first, on the upper part of the web. <div class="figcenter"> <ANTIMG src="images/i_272.jpg" alt="the Garden Spider’s web " /></div> <h3>THE STICKY SNARE</h3> The spiral part of the Garden Spider’s web is a wonderful contrivance. The thread that forms it may be seen with the naked eye to be different from that of the framework and the spokes. It glitters in the sun, and looks as though it were knotted. I cannot examine it through the microscope outdoors because the web shakes so, but by passing a sheet of glass under the web and lifting it I can take away a few pieces of thread to study. The microscope now shows me an astounding sight. Those threads, so slender as to be almost invisible, are very closely twisted twine, something like the gold cord of officers’ sword-knots. Moreover, they are hollow. They contain a sticky moisture resembling a strong solution of gum arabic. I can see it trickling from the broken ends. This moisture must ooze through the threads, making them sticky. Indeed, they are sticky. When I lay a straw flat upon them, it adheres at once. We see now that the Garden Spider hunts, not with springs, but with sticky snares that catch everything, down to the dandelion-plume that barely brushes against the web. Nevertheless, the Spider herself is not caught in her own snare. Why? For one thing, she spends most of her time on her resting-floor in the middle of the web, which the spiral does not enter. The resting-floor is not at all sticky, as I find when I pass a straw against it. But sometimes when a victim is caught, perhaps right at the end of the web, the Spider has to rush up quickly to bind it and overcome its attempts to free itself. She seems to be able to walk upon her network perfectly well then. Has she something on her feet which makes them slip over the glue? Has she perhaps oiled them? Oil, you know, is the best thing to prevent surfaces from sticking. I pull out the leg of a live Spider and put it to soak for an hour in disulphide of carbon, which dissolves fat. I wash it carefully with a brush dipped in the same fluid. When the washing is finished, the leg sticks to the spiral of the web! We see now that the Spider varnishes herself with a special sweat so that she can go on any part of her web without difficulty. However, she does not wish to remain on the spiral too long, or the oil might wear away, so most of the time she stays on her safe resting-floor. This spiral thread of the Spider’s is very quick to absorb moisture, as I find out by experiment. For this reason the Garden Spiders, when they weave their webs in the early morning, leave that part of the work unfinished, if the air turns misty. They build the general framework, they lay the spokes, they make the resting-floor, for all these parts are not affected by excess moisture; but they are very careful not to work at the sticky spiral, which, if soaked by the fog, would dissolve into sticky threads and lose its usefulness by being wet. The net that was started will be finished to-morrow, if the weather is right. But on hot days this property of the spiral is a fine thing; it does not dry up, but absorbs all the moisture in the atmosphere and remains, at the most scorching times of day, supple, elastic, and more and more sticky. What bird-catcher could compete with the Garden Spider in the art of laying snares? And all this industry and cunning for the capture of a Moth! Then, too, what a passion the Spider has for production. I calculated that, in one sitting, each time that she remakes her web, the Angular Spider produces some twenty yards of gummy thread. The more skillful Silky Spider produces thirty. Well, during two months, the Angular Spider, my neighbor, renewed her snare nearly every evening. During that time she manufactured something like three quarters of a mile of this tubular thread, rolled into a tight twist and bulging with glue. We cannot but wonder how she ever carries so much in her little body, how she manages to twist her silk into this tube, how she fills it with glue! And how does she first turn out plain threads, then russet foam, for her nest, then black stripes to adorn the nest? I see the results, but I cannot understand the working of her factory. <div></div> <div style="break-after:column;"></div>

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