SPIDERS. 



115 



Fig. 162. — Spinnerets of Amawrobius. 

 a. Cribellum. 



large round-web spiders, for practical purposes, either by carding the cocoons or by 

 drawing the thread directly from the spider. The latest experiments and plans for 

 this purpose are those of Professor Wilder. He shows how Nephila plumipes might 

 be raised in large numbers, each spider kept by herself in a wire ring surrounded by 

 water, fed with flies bred for the purpose from old meat, and milked every day of their 

 thread. Every day or two each spider should be 

 taken down, put into a pair of stocks, and the thread 

 pulled out till it stops coming. In this way he thinks 

 an ounce of thread could be got from each spider 

 during the summer. The thread is from a seven- 

 thousandth to a four-thousandth of an inch thick, 

 and much smoother and more brightly colored, as 

 well as finer, than that of the silk-worm. Several 

 threads would have to be twisted together to get 

 one of manageable size. The principal difiiculties 

 are the space needed for keeping each spider by 

 herself, and the amount of labor needed to pro- 

 vide them with living insects for food and to draw 

 out the silk, which would make it too expensive 

 to use. 



The Ciniflonidse, in addition to the usual plain thread, make a peculiar kind of 

 their own. They have in front of the spinnerets an additional spinning-organ, called 



the cribellum. It is covered with fine 

 tubes, much finer than those of the spin- 

 nerets, set close together. They also 

 have on the last joint but one of the 

 hind-legs a comb of stiff hairs, the cala^ 

 mistrum. 



When they spin their peculiar web 

 they turn one of the hind-legs across under the spinnerets, so that the calamistrum is 

 just under the cribellum, and the foot rests on the opposite leg (Fig. 164). The hind- 

 legs are then moved rapidly back 

 and forth, so that the calamistrum 

 combs out from the spinning-tubes, 

 and at the same time tangles a 

 band of fine threads. This band 

 is laid along, and attached here 

 and there to a plain thread, so as 

 to make it adhere more readily to 

 an insect that happens to touch 

 it. As one leg gets tired, they 

 change and work with the other, 

 can be seen with the naked eye. 



Among those spiders that use the calamistrum is one which makes a web unlike any 

 other. It has been described by Professor Wilder under the name of the triangle 

 spider. It lives usually among the dead branches around the lower part of pine and 

 spruce trees, and is colored so like the bark that when it stands, as it usually does, on 

 the end of a branch it is easily mistaken for a part of it. The web seems to be made 



Fig. 163. — Calamistrum of Amaurobius 



Fig. 164. - 



■ Dlctyna, spinning curled web. 

 c. Curled thread. 



a. b. Smooth thread. 



In the webs of these spiders this adhesive band 



