The romance of the animal world

by Edmund Selous

For my part I think it is only permissible to use the word “mimic,” in this relation, in order to give a vivid impression, not indeed of the thing, but of what the thing seems to be—to arouse interest in it, in fact, which is why I have done so here. But when the process is known the word had better be dropped—at least, in works that really profess to be scientific. This, of course, does not.

CHAPTER XIII

SPIDERS AND THEIR WEBS—TRAP-DOOR SPIDERS—SPIDERS THAT EAT BIRDS—AQUATIC SPIDERS—BORN IN A DIVING-BELL.

Though we have already had something to say about spiders, they are such interesting creatures that we may as well devote a few pages more to them—especially as the web, which is their most salient peculiarity, has as yet hardly been mentioned. The beauty and ingenuity of this wonderful fabric has always aroused the interest and admiration of mankind, and will doubtless continue to do so, as long as spiders and men exist together on the earth. Our own common garden or geometric spider is as good a web-spinner, perhaps, as any that exists, or, if not, it is at least as good as any that I can think of at the moment. Everyone is familiar with the general appearance of the web and the mathematical regularity of its outline, whilst all who have watched its construction must have been astonished at the skill displayed by the spider, both in the weaving and placing of it. It is composed of two separate parts, the first, or framework, consisting of a number of stout, yet delicate, cables, which radiate outwards from a common centre, whilst around them a finer thread, quite distinct in its structure, is wound spirally, in wider and wider circles, the last of which makes the circumference. The quality of the thread, composing these two divisions of the web, is as distinct as the parts themselves, for whereas “the radiating lines are smooth and not very elastic, the spiral one is thickly studded with minute knobs, and is elastic to a wonderful degree, reminding the observer of a thread of india-rubber. It is to the little projections that the efficacy of the net is due, for they are composed of a thick adhesive and viscid substance, and serve to arrest the wings and legs of the insects that happen to touch the net.”[12] “As the radii,” says Mr. Blackwell (a great authority on British spiders), “are inadhesive, and possess only a moderate share of elasticity, they must consist of a different material from that of the viscid spiral line, which is elastic in an extraordinary degree. Now, the viscidity of this line may be shown to depend entirely upon the globules with which it is studded, for if they be removed by careful application of the finger, a fine glossy filament remains, which is highly elastic, but perfectly inadhesive. As the globules, therefore, and the line on which they are disposed, differ so essentially from each other, and from the radii, it is reasonable to infer that the physical constitution of these several portions of the net must be dissimilar. An estimate,” continues Mr. Blackwell, “of the number of viscid globules distributed on the elastic spiral line, in a net of Epeira apoclisa, of a medium size, will convey some idea of the elaborate operations performed by the Epeira in the construction of their snares. The mean distance between two adjacent radii, in a net of this species, is about seven-tenths of an inch; if, therefore, the number seven be multiplied by twenty (the mean number of viscid globules which occur on one-tenth of an inch of the elastic spiral, at the ordinary degree of tension), the product will be 140, the mean number of globules deposited on seven-tenths of an inch of the elastic spiral line. This product, multiplied by twenty-four, the mean number of circumvolutions described by the elastic spiral line, gives 3,360, the mean number of globules contained between two radii; which, multiplied by twenty-six, the mean number of radii, produces 87,360, the total number of viscid globules in a finished net of average dimensions. A large net, fourteen or sixteen inches in diameter, will be found, by a similar calculation, to contain upwards of 120,000 viscid globules, and yet Epeira apoclisa will complete its snare in about forty minutes, if it meet with no interruption.”

And yet, in the execution of these beautiful and elaborate webs, the fine threads of which are placed with such nicety, and at such regular distances one from another, that they have procured for their manufacturers the specific title of “geometric,” the spider is guided entirely by the sense of touch. This is proved by the fact that when confined in total darkness it will spin webs as truly as by daylight; but the test is hardly necessary, since, as the eyes of the spider are situated on the front part of its head, whereas the threads issue from the spinnarets at the extremity of its body and are guided by the hind pair of legs, sight, it is evident, could hardly aid in the process. Does reason, therefore, enter into the process of web-making, or is it merely an instinctive one? This being a difficult question to answer, instead of doing so I will quote the minute and interesting account given by Thompson in his Passions of Animals of how the spider spins its web under ordinary conditions, premising, however, that, in almost every point, different people, who all write as though they had been witnesses of what they describe, appear to differ in their opinion. This remark applies also to the structure of the thread itself, for whilst Wood and Blackwell, as we have just seen, say that this differs essentially in the two parts of the web, Kirby and Spence, who are followed by Professor Romanes, believe it to be one and the same. Büchner, too, speaks of the “high degree of elasticity” of the radii as against the “moderate share” of it, which is all that Blackwell allows them, and so on—ample encouragement this, surely, to observe spiders for ourselves, since whatever we may think, there is sure to be someone respectable to agree with us.

Thompson’s account is as follows: “The web of the garden spider—the most ingenious and perfect contrivance that can be imagined—is usually fixed in a perpendicular or somewhat oblique direction, in an opening between the leaves of some plant or shrub; and as it is obvious that round its whole extent lines will be required to which those ends of radii that are farthest from the centre can be attached, the construction of those exterior lines is the spider’s first operation. It seems careless about the shape of the area they are to enclose, well aware that it can as readily inscribe a circle in a triangle as a square; and in this respect it is guided by the distance or proximity of the points to which it can attach them. It spares no pains, however, to strengthen and keep them in a proper degree of tension. With the former view it composes each line of five or six, or even of more threads, glued together; and with the latter it fixes to them from different points a numerous and intricate apparatus of smaller threads; and having thus completed the foundation of its snare, it proceeds to fill up the outline. Attaching a thread to one of the main lines, it walks along it, guiding it with one of its hind legs, that it may not touch in any part and be prematurely glued, and crosses over to the opposite side, where, by applying its spinners, it firmly fixes it. To the middle of this diagonal thread which is to form the centre of its net, it fixes a second, which, in like manner, it conveys and fastens to another part of the lines including the area. The work now proceeds rapidly. During the preliminary operations it sometimes rests, as though its plan required meditation; but no sooner are the marginal lines of the net firmly stretched, and two or three radii spun from its centre, than it continues its labour so quickly and unremittingly that the eye can scarcely follow its process. The radii, to the number of about twenty, giving the net the appearance of a wheel, are speedily finished. It then proceeds to the centre, quickly turns itself round, pulls each thread with its feet, to ascertain its strength, breaking any one that seems defective, and replacing it by another. Next it glues immediately round the centre five or six small concentric circles, distant about half a line from each other, and then four or five larger ones each separated by the space of half an inch or more. These last serve as a sort of temporary scaffolding to walk over, and to keep the radii properly stretched, while it glues to them the concentric circles that are to remain, which it now proceeds to construct. Placing itself at the circumference, and fastening its thread to the end of one of the radii, it walks up that one towards the centre to such a distance as to draw the thread from its body of a sufficient length to meet the next. Then stepping across and conducting the thread with one of its hind legs, it glues it with its spinners to the point in the adjoining radius to which it is to be fixed. This process it repeats until it has filled up nearly the whole space from the circumference to the centre with concentric circles, distant from each other about two lines. It always, however, leaves a vacant interval around the smallest first-spun circles that are nearest to the centre, and bites away the small cotton-like tuft that united all the radii, which being held now together by the circular threads have thus, probably, their elasticity increased; and in the circular opening resulting from this procedure it takes its station and watches for its prey, or occasionally retires to a little apartment formed under some leaf, which it also uses as a slaughter-house.”

The lair thus formed is connected with the web by means of a thread along which the vibrations caused by the struggles of any captured insect are carried, thus apprising the spider, who, if angry, rushes out to seize her victim. It is a very amusing thing to strike a tuning-fork on some hard substance, and then touch the net with it. The spider, full of excitement, darts towards the area of disturbance, but is bewildered at finding nothing, where the bag seemed so obvious. She may be thus lured out several times in succession, but at length does not come, showing that she can adapt her psychology to an experience which must be for her altogether unprecedented. I have compared her, on these occasions, with a sceptic at a séance, when something had unmistakably and unaccountably happened.

More interesting, perhaps, even than the making of the web, is the way in which the spider will sometimes weight it in order to make it steady when a high wind is blowing. There is no doubt about this, as it has been observed by many persons on as many different occasions. I will therefore quote an account at second-hand, as it was given to the late Mr. Wood by one of his friends who was accustomed to watch spiders in his verandah. “One day,” says Wood, “a sharp storm broke out and the wind raged so furiously through the garden that the spiders suffered damage from it, although sheltered by the verandah. The mainyards of one of these webs, as the sailors would call them, were broken, so that the web was blown hither and thither, like a slack sail in a storm. The spider made no fresh threads, but tried to help itself in another way. It let itself down to the ground by a thread and crawled to a place where lay some splintered pieces of a wooden fence thrown down by the storm. It fastened a thread to one of the bits of wood, turned back with it, and hung it with a strong thread to the lower part of its nest, about five feet from the ground. The performance was a wonderful one, for the weight of the wood sufficed to keep the nest tolerably firm, while it was yet light enough to yield to the wind and so prevent further injury. The piece of wood was about two and a half inches long, and as thick as a goose quill. On the following day a careless servant knocked her head against the wood and it fell down. But in the course of a few hours the spider had found it and brought it back to its place. When the storm ceased, the spider mended her web, broke the supporting thread in two, and let the wood fall to the ground.” What, it may be asked, could a man have done more? If people were really governed by evidence in their opinions on a great many subjects—for that they are is one of the greatest fallacies in the world—this one case would be sufficient to establish the reasoning powers of all animals standing not lower in the scale than spiders, whilst other instances as good lower down would take it up to them in the same way. But one really believes according to one’s wishes, and it is quite surprising that this fact—which can be verified by anyone—is not more generally recognised than it is.

Wonderful as are the webs which are spun by many spiders for the purpose of entrapping their prey, the houses which some of them make and live in, are, perhaps, even more extraordinary. The trap-door spiders inhabit various parts of the world, but are found in most abundance, or, at least, have attracted most attention, in the island of Jamaica. They, all of them, make a long tunnel or gallery, going down at a steep slant into the earth, and round the sides of this they spin a close web, which makes a strong, durable lining. This lining is double, and whilst the inner layer is soft and smooth like silk, the outer one, in which the spider lives, is so rough and flaky that it both looks and feels more like felt, or rough paper, or the bark of a tree, than a substance usually so delicate as the web of a spider. This roughness, however, is just what is required, since it enables the spider to run up and down its little tube, or tunnel, with the greatest ease. But the most wonderful part of this ingenious dwelling is the trap-door, at its entrance, from which the spider takes its name, and by which it has become famous. This, also, is woven by the spider, and is one in substance with the tube, to which it forms a little door, or lid, which fits its orifice as exactly as does the lid of a neatly made box. Like a box, too, it is attached to the tube by a hinge, the web, at the jointure, being spun in such a manner that we may well give it this name. Before the spider can either enter or leave its tube, the lid of it has to be lifted, and both the creature and its dwelling become, then, conspicuous objects. Once in or out, however, the lid drops, and as it fits into, as well as over, the orifice, there is then no break in the surface of the ground. Still, if the lid were made only of web, it would be discernible by close observation, since a little round patch of another material would be, as it were, let into the ground. The spider, however, as if fearing this, covers the exterior of the lid with earth which it brings from near about, and by the use of a gummy secretion which it has the power of exuding, causes to adhere to it. The lid, therefore, becomes practically a part of the surrounding earth, from which, when no longer raised above its surface, it is impossible to distinguish it.