Of all the marvellous things of which the lower creatures are capable, certainly one of the most wonderful is their power of spinning threads of the most beautiful fineness, some of which we know as 'silk,' while for others we have no special name.

Though insects are—at least, from our point of view—the most important of the world's spinners, yet they are not the only creatures who possess this secret, for the spiders and mussels and the pearl oyster have also shown themselves very wonderful spinners.

The purposes for which the fine thread is spun are very different. Caterpillars use it chiefly as a means of providing a warm covering while in the chrysalis stage: so also do some beetles. The spider uses its silk to build cunning traps for unwary flies. The mussel lying below the surface of the sea employs its power as a spinner to construct a cable, which, being fastened to the rocks on the sea-bed, prevents the otherwise helpless mussel from being washed away.

In the silkworm (fig. 1) the silk is produced by certain peculiar structures, tube-like in shape, known as the silk-glands. The silk is created in a liquid form in the inside of the silk-gland, and, becoming mixed with a kind of gum, is forced through a sort of mechanical press, from which it comes through the mouth in the form of the delicate threads which we know as 'silk.'

This silk is used by caterpillars for various purposes, and varies much in quality: that spun by silkworm caterpillars is much prized by man. The caterpillar uses it to form a case for the protection of its body when turning into a chrysalis, from which it will emerge later a full-grown moth.

When spinning, the caterpillar begins by sending out the end of a thread which is quite soft and sticky. This immediately sticks to the object to which it is attached. This done, every movement of the caterpillar's head draws a fresh piece of the silk thread from its mouth. When spinning a cocoon, the thread is made to form a long, oval, egg-shaped case around the body of the caterpillar. But sometimes, as in the case of those caterpillars which live in companies, it is used to form a sheet or tent within which the tent-makers dwell. Other caterpillars use the power of weaving silk as a means of escape from enemies. When in danger they let themselves down on to the ground by attaching the end of a thread to a leaf or twig, and then dropping off, leaving the thread to be drawn from the mouth by the weight of the body as it falls.

Under the microscope each thread of silk is seen to be double: the total length of the thread when unwound from the cocoon is over a thousand feet. Over four hundred different kinds of silk-producing caterpillars are known.

The spinning glands of the spider are placed at the tail end of the body, but the threads spun therefrom, though strong, are of little use for commercial purposes. Silk fabrics have, however, been made from spider webs, but these are only curiosities.

The silk, or, as we may call them, the spinning glands, consist of from two to four pairs of organs, or 'spinnerets,' placed together in a small cluster. The threads which they form are made, as in the case of the silk of the caterpillar, of a sticky fluid, which, when drawn out through the tiny holes of the spinnerets, and exposed to the air, form fine threads, and these combining together form the silky thread with which we are familiar.

One of the principal uses of the silk threads is to form nets to catch small insects. These nets are often—as is the case of the garden spider, for example—very beautiful. In their construction the greatest skill is shown. The method is briefly as follows: First of all a large five-sided frame is formed; then long threads, which are rather like the spokes of a wheel, are added. These harden at once, and to them are attached the cross-threads, which form the delicate network of the complete web. But if the web be examined with a strong magnifying glass, there will be found, among the network, a number of threads bearing little drops of a sticky substance (fig. 2). These are made by special glands, and differ from the ordinary threads in that they do not dry on being exposed to the air. They serve the purpose of bird-lime—that is to say, they are there to aid in entangling insects which fly up against the web. Having spread his net, the spider returns to a little shelter woven on the under side of a leaf. Here he waits for his victims, holding in one of his claws a long, delicate thread attached to the web, so as to serve as a means of communication with the trap, the vibrations set up by the struggles of the captive giving warning by shaking the communication cord! He then rushes out, if the victim be small, and throwing himself upon the wretched prisoner, sucks him dry and cuts away the web so as to release the empty carcase. Should a wasp or bee happen to be caught, the proceedings are much more cautious, and the spider himself often proves the victim.

Spiders when small often use their spinnerets much as the witches of old were supposed to use a broom-stick—that is to say, as a means of travelling through the air. Turning the end of the body upwards they force out a few threads, which, caught by the breeze, are blown away, and so a number of long threads are rapidly drawn out, sufficiently long at last to carry the spider itself with them. When too heavy to fly, they sometimes send a thread adrift and wait until it catches in some projecting bough; this done, they make fast the end to the bough or leaf on which they may be resting, and climb along this tight-rope to build a new home.

The floating threads formed by broods of small spiders are sometimes very numerous, and cover everything: they are especially noticeable in hedges, and are one of the causes of what is called in the country 'Gossamer.'

W. P. Pycraft, F.Z.S., A.L.S.