INSECTS AND THEIR NEAR RELATIVES 



The egg-sacs of the different species of spiders vary greatly in form. 

 In some, as in that figured below, the outer covering is very dense, while 



Fig. 20. — Egg-sac of Argiope. 



Fig. 21. — Lycosa with thin egg-sac. 



in others the outer part consists of thin flossy silk (Fig. 21). One of the 

 most common kinds is very flat, silvery in color, and is firmly attached 

 to stones lying upon the ground (Fig. 22). 



Every one knows that a spider wishing to descend 

 to some place beneath it simply fastens a line to the 

 object which it is upon and then drops boldly off, regu- 

 lating the rate of its descent by spinning the line 

 rapidly or slowly; when the spider wishes to return, it 

 has only to climb up the same line. 



Frequently spiders pass from point to point in a F IG - . ? 3 - — E es sac on 



, . 7 1 i- . • 1 r "11 i • 1 rr-M under side of a stone. 



horizontal direction by means of silken bridges. I hese 

 are formed in this way: the spider spins out a thread, which is carried off 

 by a current in the air. After a time the thread strikes some object and 

 adheres to it; then the spider pulls the line tight, and fastens it where it 

 is standing. It then has a bridge, along which it can easily run. 



But more remarkable than either of these uses of silk for locomotion is 

 the fact that many spiders are able to travel long distances, hundreds of 

 miles, through the air by means of these silken threads — 



"sailing mid the golden air 

 In skiffs of yielding gossamere." — (Hogg.) 



The aeronautic spiders, or flying spiders, as they are more commonly 

 called, are frequently very abundant, especially on warm autumn days. 

 At such times innumerable threads can be seen streaming from fences, 

 from bushes, and the tips of stalks of grass, or floating through the air. 

 The flying spider climbs to some elevated point, which may be merely 

 the tip of a stalk of grass, and then, standing on the tips of its feet, lifts 

 its body as high as it can, and spins out a thread of silk. This thread is 

 carried up and away by a current of air. When the thread is long enough 

 the force of the air current on it is sufficient to buoy the spider up. It 

 then lets go its hold with its feet and sails away. These spiders travel 

 long distances over the sea far from land in this manner. 



