248 Nature's Geometricians [FOURTH WEEK 



web, when we approach too closely, instead of deserting 

 his snare, set it vibrating back and forth so rapidly that 

 he becomes a mere blur; a more certain method of escap- 

 ing the onslaught of a bird than if he ran to the shelter 

 of a leaf. 



Those spiders which leap upon their prey instead of 

 setting snares for it, have still a use for their threads of 

 life, throwing out a cable as they leap, to break their fall 

 if they miss their foothold. What a strange use of the 

 cobweb is that of the little flying spiders! Up they run 

 to the top of a post, elevate their abdomens and run out 

 several threads which lengthen and lengthen until the 

 breeze catches them and away go the wingless aeronauts 

 for yards or for miles as fortune and wind and weather may 

 dictate ! We wonder if they can cut loose or pull in their 

 balloon cables at will. 



Many species of spiders spin a case for holding their 

 eggs, and some carry this about with them until the young 

 are hatched. 



A most fascinating tale would unfold could we discover 

 all the uses of cobweb when the spiders themselves are 

 through with it. Certain it is that our ruby- throated 

 hummingbird robs many webs to fasten together the plant 

 down, wood pulp, and lichens which compose her dainty 

 nest. 



Search the pond and you will find another member of 

 the spider family swimming about at ease beneath the 

 surface, thoroughly aquatic in habits, but breathing a 

 bubble of air which he carries about with him. When 

 his supply is low he swims to a submarine castle of silk, 



