232 AN INTRODUCTION TO ENTOMOLOGY. 



tended 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. I have not yet observed the owners of the nets taking their 

 prey from them ; but I cannot doubt that they are made to trap 

 small insects or other animals that are being carried down stream, 

 for the larvae of the sub-family to which these net-builders belong, 

 the Hydropsychince, are known to be carnivorous. It should be 

 noted here, however, that the greater number of caddice-worms are 

 herbivorous. 



There are many caddice-worms that build their cases of stones ; 

 some of these cases are very regular in form. One of the common 

 kinds resembles a slightly tapering cornucopia, made of small grains 

 of sand, cemented together with great regularity. Another consists 

 of a shorter tube, to each side of which are fastened one or two 

 larger stones, as if to keep it in position (Fig. 197). But more re- 



Figs. 197, 198.— Cases of Caddice-worms. 



markable than either of these is the case (Fig. 198) which sc closely 

 resembles in form the shell of a snail that it has been described as 

 such by several conchologists. 



We find among the caddice-worms carpenters as well as masons. 

 And there exists among the builders of wood as great a variety of 

 architectural tastes as among the builders of stone. Probably the 

 most familiar of the forms of cases made of wood is that represented 

 in Fig. 199. This is made of irregular pieces of wood arranged in a 



Figs. 199, 200.— Cases of Caddice-worms. 



longitudinal manner. Much more likely to attract attention is the 

 case composed of sticks placed at right angles to the body (Fig. 200). 



