150 SCORPIONS, SPIDERS, AND TICKS 



ones so that only the fittest ones survive to become adults 

 m the spring. 



Forest paths are often crossed by threads of spider's 

 silk. A spider climbs to the end of a branch and spins out 

 a thread which is caught by the breeze and wafted across 

 the path, where the end becomes entangled in a branch on 

 the opposite tree. 



Certain spiders, known as the ballooning, or flying spiders, 

 climb to the end of a post or to the tip of a plant and spin 

 silk into the air which is caught and wafted away by the 

 breeze. When enough is spun to support the spider, it 

 lets go and is borne away by the currents of air. These 

 spiders travel long distances in this manner, as shown by 

 the fact that they have been seen floating through the air at 

 sea far from land. 



The spiders that build the irregular webs, termed cob- 

 webs, in dwelhng houses belong to the family of cobweb 

 weavers. They are small spiders with very sUm legs, and 

 there are many different species of them. By far the larger 

 number live in the fields and spin their webs on bushes. 



Those webs spun by the spiders known as orb weavers 

 are marvels of ingenuity and regularity of construction. 

 The webs are common on bushes, fences, weeds, etc. (Fig. 

 88) , but are usually given little attention. The outer frame- 

 work of supporting threads is often very irregular; but the 

 radiating lines are placed at regular intervals from each 

 other, and the spiral is laid on these in a regular manner. 



The radii are dry and inelastic, while the spiral thread 

 is sticky and elastic. Some of the orb weavers spin a zig- 

 zag band, or ribbon, across the center of the web, evidently 

 to strengthen it. Many of the orb weavers are small 

 spiders, but some are large. The funnel web weavers spin 



