152 



INSECT LIFE. 



FIG. 123. Net of a net-building 

 caddice-worm. 



in this rude retreat is a fisherman, and stretched be- 

 tween two stones near-by can be seen his net. 



This is made of silk. It is usually funnel-shaped, 

 opening 1 up-stream, and in the center of it there is a 

 portion composed of threads of silk extending in two 

 directions at right angles to each other, so as to form 



meshes of surprising regu- 

 larity. It is as if a spider 

 had stretched a small web 

 in the water where the cur- 

 rent is swiftest (Fig. 123). 



These nets occur in rap- 

 ids between stones, but in 

 many places they are to be 

 found in greater numbers 

 along the brinks of falls. 

 Here they are built upon the surface of the rock, 

 in the form of semi-elliptical cups, which are kept 

 distended by the current. Much of the coating of 

 dirt with which these rocks are clothed in summer 

 is due to its being caught in these nets. 



It is usually difficult to procure specimens of these 

 nets for preservation ; sometimes, however, one can 

 be found attached to the surface of a single small 

 stone or to a piece of wood in such a way that it can 

 be removed from the water without injury to it. 



Find some net-building caddice-worms and learn 

 all you can regarding their ways ; collect specimens 

 for your collection and for study ; compare their 

 structure with that of other caddice-worms ; pre- 

 serve specimens of larvae in alcohol ; and dry, if pos- 

 sible, some of their nests and nets. 

 Write an account of these insects. 



