CLASS ARACHNIDA 



305 



struggling prey, and sometimes in making a broad, wavy band across 

 the center of the web. Larger threads are used in the construction of the 

 web itself. 



The spiders make use of two kinds of silk, one of which is dry and 

 inelastic, the other viscid and elastic. In the orb web, which may be 

 taken as a type, the framework is composed of threads made up of the 

 first kind of silk, while the spiral threads which pass around the web 

 from one radiating thread to the next are made of silk of the second kind. 

 If examined with a lens this viscid and elastic silk will be found to have 

 numerous beadUke masses of sticky material which help to hold the prey 

 when it touches the web. It is supposed that these two kinds of silk 

 are spun from different spinnerets. 



Fig. 208. — Wolf spider, Lycosa helluo. A, female carrying a sac of eggs. B, a few 

 weeks later; the eggs have hatched and the spiderlings are being carried upon the back of 

 the mother. {Photographed and contributed by Edson H. Fichter.) 



Silk is used not only to line a nest or form a web but also to fashion 

 the cocoon. Some spiders spin an anchor line by means of which they 

 may return to a certain point from which they have leaped or fallen. 

 Others make bridges of silk, spinning threads off into the air until they 

 become attached to some object on the farther side of a space; the lines 

 are then drawn taut by the spider. Still other spiders make use of silk 

 in the construction of balloons, spinning a loose mass of threads which 

 are sufficient to buoy the animal up and enable it to be carried along by 

 the wind. These aeronautic or flying spiders have been known to travel 

 many miles in this fashion. 



328. Behavior. — Spiders can see but a very short distance, apparently 

 distinctly only within a radius of four or five inches. They do not seem 

 to use other senses, except the one of touch, but that sense is exceedingly 

 delicate, especially on the pedipalpi and on the terminal joints of the 

 legs. Spiders act largely from instinct but they form some habits and 



