64 NATURE STUDY 



can ; find cases with the head and fore part of the body of the 

 worm projecting ; find cases moving, i. e., dragged by the slowly 

 walking caddis-worm, Examine a caddis-worin carefully ; note 

 its long, soft, grub-like body ; note that the head and the front 

 pait of the body from which arise 

 .the legs, namely, that part of the 

 [body which projects from the case, 

 'has a strong, hard outer wall. 



What is the Case for ? To protect Fig. 37. Young Caddi-e fly in its case 



the soft, defenseless caddis-worm madeof pebblesandbitsofwood ' 

 from the many predacebus animals which live in the brook. 

 Why is the head and front part of the body so much harder than 

 the rest of the body? Can you easily pull the caddis-worm out 

 'of its case ? How does it hold itself so firmly in its case ? By 

 the pair of ptrong hooks (legs) which are located on the posterior 

 tip of the body. Note that the front pair of legs (how many 

 pairs are there ?) are longer than one would expect to find on such 

 a worm-like insect ; what is the reason for this condition of the 

 legs? How does the caddis- woim breathe ? 



Not all of the caddis-worms live in cases, and some which 

 'make cases do not remain in them all of the time, so that you may 

 sometimes find caddis-worms crawling about on the stones. 

 Some of these home-leaving caddis- worms make tiny nets of silk 

 stretched between two near-by stones. These nets are ''usually 

 funnel-shaped, opening up-stream and in the center of them there 

 is a portion composed of threads of silk extending in two direc- 

 tions at right angles to each other, so as to form meshes of sur- 

 prising regularity. It is as if a spider had stretched a small web 

 in the water where the current is swiftest" The caddis- worms 

 Iwhich build these nets live in rude cases on the under side of 

 stones. The cases are composed of an inner silken tube partly 

 covered with little pebbles. 



All these caddis- worms are the young, or larvae, of caddis- 



