SHEET-BUILDING SPIDERS 151 



webbing was complete to satisfaction. There is no 

 geometrical accuracy in this structure. Nor is there 

 any viscidity in its lines save at the points of attach- 

 ment of the filaments. Insects are captured by 

 entanglement in the fine meshes and not by adherence 

 to its lines. 



Instantly an insect alights on the snare its feet and 

 wings become entangled in the meshes. With a little 

 struggling it can usually break free, but the hungry, 

 evil-looking spider, crouching near the mouth of its 

 retreat, dashes at terrific speed across the snare and 

 seizes its victim before it can escape. It is a most 

 extraordinary fact that a spider can move about so 

 freely on the snare without ever getting its own legs 

 entangled in the meshes. With a magnifying glass it 

 can be easily seen that the spider possesses three little 

 curved claws at the tips of the tarsi, and that at every 

 step these claws hook over a filament of the web. If 

 the tips of the claws be removed with a fine pair of 

 scissors the spider will move over its snare with much 

 greater difficulty, hooking up a thread here and there, 

 though it will not become entangled. It is difficult to 

 understand how the claws never succeed in becoming 

 caught in the meshes and impeding the progress of the 

 spider, yet this never occurs no matter how tattered and 

 broken the snare may be. It is strange to witness a 

 spider darting with such incredible speed over its 

 snare that its movements are almost impossible to 

 follow, and to recognize that at every one of the little 

 steps that go to make each movement, twenty-four 

 tiny curved claws are hooked over various filaments in 

 the web, and that these claws, though apparently just 

 the very implements suitable for entanglement, are 



