228 ILLINOIS ACADEMY OF SCIENCE 



but it is known that many of them live through the winter 

 as larvae and transform in June or July. When the larvae 

 are ready to pupate they either fasten the case to some larger 

 object, and close the other end, or they close both ends with a 

 web of silk and frequently fasten on a pebble or a bit of stick. 

 They are completely helpless while transforming. The pupae 

 differ from the larvae in having larger mandibles with which 

 they cut their way out of the case, and usually swimming hairs 

 on the mesothoracic legs. Most of the larvae which inhabit 

 movable cases transform to pupae which have respiratory fila- 

 ments much like the larvae. The pupae have rows of hooks on 

 several dorsal segments which hold them in the case. 



The larvae, which live in fixed cases, build them in the 

 same way. Sometimes their cases are only tubes of silk, 

 which are found on the bottom of the stream or on the sur- 

 face of sticks and stones. Others are of various shapes and 

 generally covered with sand, pebbles, or leaves. Certain spe- 

 cies build their cases in the form of a snail's shell, which are 

 covered with sand, and some of these were described as snails' 

 shells. 



The larvae inhabiting these fixed cases are mostly of another 

 type of body, which is not as strongly curved. They have no 

 hooks to hold them to the cases, and although the majority 

 breathe by means of respiratory filaments, a number of them 

 breathe by means of spiracles. They pupate in much the same 

 way as the larvae inhabiting movable cases and the pupae 

 strongly resembles the larvae, differing in the larger man- 

 dibles and the swimming hairs on the mesothoracic legs. In 

 some species the respiratory filaments are lost during pupa- 

 tion and the pupa breathes by means of one large spiracle lo- 

 cated in the conjunctiva between the prothorax and mesotho- 

 rax. 



The most interesting species of larvae with fixed cases are 

 those that spin nets, with which they catch their food. These 

 nets are placed in the streams where the current is swift. They 

 are usually spun somewhat funnel-shaped, so that the current 

 keeps them expanded. These larvae often do not build a case 

 but hide in masses of rubbish near where they have spun their 

 nets. Those which spin cases often place them side by side, 

 so that there is quite a colony. 



