TROUT STREAM INSECTS 111 



" When the caddis worms are ready to trans- 

 form they withdraw wholly into the case and 

 close the opening with a loose wall of stones 

 or chips and silk. This wall keeps out enemies, 

 but always admits the water which is necessary 

 for respiration. . . . When ready to issue 

 the pupa usually comes out from the submerged 

 case, crawls up on some support above water 

 and there moults, the winged imago soon fly- 

 ing away. Some kinds, however, emerge from 

 the water, Comstock observed the pupa of one 

 of the net-building kinds to swim to the sur- 

 face of the water. . . . The instant the 

 creature was free from the water the wings 

 expanded to their full size and it flew away 

 several feet. . . . The time required for 

 the insect to expand its wings and take its first 

 flight was scarcely more than one second; cer- 

 tainly less than two. As such caddis flies 

 normally emerge from rapidly flowing streams 

 which dash over rocks, it is evident that if much 

 time were required for the wings to become 

 fit for use, as is the case with most other in- 

 sects, the wave succeeding that which swept one 

 from the water would sweep it back again and 

 destroy it. 



:< The adult caddis flies . . . are mostly 

 obscurely colored, rather small moth-like 



