2 AMERICAN SPIDERS 



important thing in its life, the factor that has largely determined 

 its physical form and dominant place in nature. 



Almost alone among the lesser creatures the spider prepares a 

 trap to capture its prey. By their structure these traps are identified 

 as tube webs, purse webs, sheet webs, tangled webs, and orb webs. 

 Sometimes they are complex structures of very curious form. 



The orb web (PI. I and PL III) has long been a symbol of the 

 spider in the mind of man, who sees in its shimmering lightness and 

 intricate, symmetrical design a thing of wonder and beauty. Such 

 esteem is well merited, for the orb web is the most highly evolved 

 of all the space webs developed by the sedentary spiders. It repre- 

 sents a triumph in engineering worthy of great mechanical inge- 

 nuity and learning; yet it was arrived at by lowly spiders, which 

 even by their most ardent supporters are credited with hardly a 

 gleam of what is called intelligence. The ingredients of almost un- 

 limited time, of moderate compulsion to irresistible change, and the 

 stimulus of real advantages gained have contrived to produce the 

 two-dimensional orb web from the seemingly wasteful tangle of 

 threads that is its origin. Instinctively and blindly the spider has 

 followed the long path leading to its symmetrical masterpiece. The 

 orb weavers are virtually slaves of their webs and have wagered 

 their future on the tenuous lines. Within the limits of their circum- 

 scribed world they are supreme autocrats, but when brushed from 

 their snares, many are clumsy, vulnerable creatures. 



In accomplishing the purpose of entangling flying insects, the 

 web has served the needs of the spider admirably and at remarkably 

 small cost. Only about an hour is consumed in spinning the average 

 orb web, which, because of great damage to the lines, frequently is 

 replaced every suitable night by the methodical spider. Yet within 

 the orb- weaving group there are some members that have broken so 

 completely with the past that they do not spin orb webs at all but 

 have substituted an entirely different method of securing their prey. 

 Instead of relying on the static but dependable round web, they 

 spin a line, weight the end with a sticky drop of liquid silk, and hurl 

 it much as the gaucho throws his bolas or the angler casts his line. 

 One need not travel to the exotic tropics to find these bolas spiders; 

 they live over most of the United States and even within large 

 cities, seeming to prefer the trees of our formal parks. Close rela- 

 tives of the bolas spiders live in Australia and Africa; one of these 

 African cousins varies the casting procedure by spinning its line 

 around like a whirligig. 



