“No. 2. November 15th. In another vessel, also furnished with Stratiotes, I placed six Argyronetræ (water-spiders). The one now referred to began to weave its beautiful web, about five o’clock in the afternoon. After much preliminary preparation it ascended to the surface, and obtained a bubble of air with which it immediately, and quickly, descended, and the bubble was disengaged from the body and left in connection with the web. As the nest was on one side, in contact with the glass, enclosed in an angle formed by two leaves of the Stratiotes, I could easily observe all its movements. Presently, it ascended again, and brought down another bubble, which was similarly deposited. In this way no less than fourteen journeys were performed, sometimes two or three very quickly one after another; at other times with a considerable interval between them, during which time the little animal was employed in extending and giving shape to the beautiful transparent bell, getting into it, pushing it out at one place, and amending it at another, and strengthening its attachments to the supports. At length it seemed to be satisfied with its dimensions, when it crept into it, and settled itself to rest, with the head downwards. The cell was now the size and nearly the form of half an acorn cut transversely, the smaller and rounded part being uppermost.... The manner,” continues Bell, “in which the spider possesses itself of the bubble of air is very curious, and, as far as I know, has never been exactly described. It ascends to the surface slowly, assisted by a thread attached to the leaf or other support, below, and to the surface of the water. As soon as it comes near the surface, it turns with the extremity of the abdomen upwards, and exposes a portion of the body to the air, for an instant, then with a jerk, it snatches, as it were, a bubble of air, which is not only attached to the hairs which cover the abdomen, but is held on by the two hinder legs, which are crossed at an acute angle, near their extremity, this crossing of the legs taking place the instant the bubble is seized. The little creature then descends more rapidly and regains its cell, always by the same route, turns the abdomen within it, and disengages the bubble.”
To its home thus ingeniously constructed the water-spider brings whatever prey it catches. Here too it lays and arranges its eggs, which are in due time hatched, so that, though an air-breathing animal, it is both born and passes the earliest days of its life beneath the surface of the water—a curious apparent, though not a real, contradiction.
CHAPTER XIV
BEAVERS AND THEIR WORK—THE DAM AND THE POND—PRACTICE WITHOUT PRINCIPLES—A USEFUL TAIL—HOW BEAVERS CUT DOWN TREES.
The beaver may be said to occupy amongst mammals the place that ants do amongst insects. Wood says of him: “Of the Social Mammalia, he takes the first rank, and is the best possible type of that group. There are other social animals, such as the various marmots and others; but these creatures live independently of each other, and are only drawn together by the attraction of some favourable locality. The beavers, on the other hand, are not only social by dwelling near each other, but by joining in a work which is intended for the benefit of the community.” As everyone knows, the beaver is an aquatic animal, as is sufficiently indicated by his appearance. He has a dense, woolly coat, which, as in the case of the otter and the still more water-loving seals, is protected by an outer covering of long, smooth hairs, which are of a reddish brown colour. The toes of the hind feet are webbed, whilst the tail is broadened out into the shape of a paddle, the blade of which, however, lies flat on the water, so that it is not used by the animal as we would use a scull or a paddle, but with an upward and downward motion. When the beaver moves his tail laterally—that is to say from side to side—as he is very well able to do, it cuts the water, after the manner and with the same effect that a scull does when worked by a seaman at the stem of the boat, instead of in the rowlocks as we use it.
Otter and Salmon.
This tail of the beaver is a very wonderful organ, and by far the most conspicuous feature about the animal. The late Mr. Morgan, who made a study of beavers and their habitations, says of it: “It is nearly flat, and covered with horny scales of a lustrous black. These scales, which are such in appearance only, cover every portion of the surface, both above and underneath. Its principal uses are to elevate or depress the head, while swimming, to turn the body and vary its direction, and to assist the animal in diving. It is also used to give a signal of alarm to its mates. When alarmed in his pond, particularly at night, he immediately dives, in doing which the posterior part of his body is thrown out of water, and as he descends head foremost, the tail is brought down upon the surface of the water, with a heavy stroke, and deep below it with a plunge. The violence of the blow is shown by the spray, which is thrown up two or three feet high.”