54 AMERICAN SPIDERS 



looked at objectively, they are quite wonderful fabrications. Their 

 tent nests are not far different from some made by gregarious 

 spiders. Many other moths spin silk, but its use is largely restricted 

 to making the cocoon. The most noted insect spinner is the silk- 

 worm, the larva of the moth Bombyx mori, which has been domes- 

 ticated for so long that it cannot now maintain itself in the wild 

 state. It produces cocoons that are easily unwound, and supplies 

 the bulk of commercial silk. The silk of moths, caddis flies, and 

 sawflies is produced in cephalic glands, which pour their contents 

 through a single opening in the lower lip. The threads are usually 

 much thicker than those of spiders. The silk is probably of only 

 one kind. 



The spider's reliance on silk is well illustrated by the many dif- 

 ferent uses to which it is put. A list of some of these is given be- 

 low, without any attempt at other than a general classification: 



Protection and Retreats 



The dragline; the bridge line; the trap line of the orb weavers; 



the warning threads of Ariadna 

 The ballooning line 

 Attachment discs to anchor the lines 

 The cells and retreats of all spiders 

 Hibernating chambers 

 Molting threads, beds, and chambers 

 Trap-door covers; spinning up of burrows and open retreats 



Protection of Eggs and Spiderlings 



The egg sacs 



The nursery webs of the Pisauridae 



Web Structures Associated ivith Mating 



The sperm web of the males 



The bridal veil of the crab spiders and other vagrants 

 The courtship and mating bowers of the black widow and sed- 

 entary spiders 

 The mating chambers of the vagrant spiders 



Structures for Stopping and Ensnaring Prey 



Sheet webs 



The stopping tangle webs of the grass spiders and the aerial sheet 

 weavers (Linyphiidae) 



