SPINNERETS.
Fig. 16.
The external spinning-organs are little two-jointed tubes on the ends of the spinnerets, [Fig. 1], L. [Fig. 16] is the spinnerets of the same spider, still more enlarged to show the arrangement of the tubes. There is a large number of little tubes on each spinneret, and in certain places a few larger ones. [Fig. 17] is a single tube, showing the ducta which leads the viscid liquid to form the thread from a gland in the spider’s abdomen. Each tube is the outlet of a separate gland. [Fig. 18], a, shows four small tubes from a spinneret of Epeira, each with a small gland attached; and [Fig. 18], b, a large tube, with one of the large glands which extends forward the whole length of the abdomen, [Fig. 5], u.
Fig. 17.
Fig. 18.
The shape of the spinnerets, and size and arrangement of the tubes, vary in different species. [Fig. 19] is a spinneret of Prosthesima, where there are a few large tubes in place of many small ones. In Agalena the two hinder spinnerets are long, and have spinning-tubes along the under side of the last joint, [Fig. 20].
When the spider begins a thread, it presses the spinnerets against some object, and forces out enough of the secretion from each tube to adhere to it. Then it moves the spinnerets away; and the viscid liquid is drawn out, and hardens at once into threads,—one from each tube. If the spinnerets are kept apart, a band of threads is formed; but, if they are closed together, the fine threads unite into one or more larger ones. If a spider is allowed to attach its thread to glass, the end can be seen spread out over a surface as large as the ends of the spinnerets, covered with very fine threads pointing toward the middle, where they unite, [Fig. 21].
Fig. 19.
Fig. 20.
The spinning is commonly helped by the hinder feet, which guide the thread, and keep it clear of surrounding objects, and even pull it from the spinnerets. This is well seen when an insect has been caught in a web, and the spider is trying to tie it up with threads. She goes as near as she safely can, and draws out a band of fine threads, which she reaches out toward the insect with one of her hind-feet; so that it may strike the threads as it kicks, and become entangled with them. As soon as the insect is tied tightly enough to be handled, the spider holds and turns it over and over with her third pair of feet, while, with the fourth pair, she draws out, hand over hand, the band of fine threads which adhere to the insect as it turns, and soon cover it entirely.
Fig. 21.
It is a common habit with spiders to draw out a thread behind as they walk along; and in this way they make the great quantities of threads that sometimes cover a field of grass, or the side of a house. We often see the points of all the pickets of a fence connected by threads spun in this way by spiders running down one picket, and up the next, for no apparent purpose.
Spiders often descend by letting out the thread to which they hang; and are able to control their speed, and to stop the flow of thread, at will. They sometimes hang down by a thread, and allow themselves to be swung by the wind to a considerable distance, letting out the thread when they feel they are going in the right direction.
Spiders in confinement begin at once to spin, and never seem comfortable till they can go all over their box without stepping off their web. The running spiders, that make no other webs, when about to lay their eggs, find or dig out holes in sheltered places, and line them with silk. Species that live under stones or on plants all line their customary hiding-places with web, to which they hold when at rest. Several of the large running spiders dig holes in sand, and line them with web, so that the sand cannot fall in; and build around the mouth a ring of sticks and straws held together by threads.