TROUT STREAM INSECTS 113 



The nymphs can run swiftly, and quickly con- 

 ceal themselves when disturbed. 



" All stone fly nymphs, as far as known, re- 

 quire well aerated water; they cannot live in 

 stagnant pools or foul streams. . . It is per- 

 fectly certain that the nymphs serve as food 

 for fishes. . . The eggs, of which 5000 or 

 6000 may be deposited by a single female, are 

 probably dropped on the surface of the water, 

 and sink to the bottom after being, however, 

 well distributed by the current. Sometimes the 

 eggs are carried about for a while by the fe- 

 male, enclosed in a capsule attached to the 

 abdomen. The young moult several times in 

 their growth, but probably not nearly as many 

 times as is common among May flies. When 

 ready for the final moulting the nymph crawls 

 out on a rock or on a tree-root or trunk on the 

 bank, and splitting its cuticle along the back, 

 issues as a winged adult. The cast exuviae are 

 common objects along swift brooks. 



" The adults vary much in size and color, 

 the smallest being less than one-fifth of an 

 inch long, while the largest reach a length of 

 two inches. Some are pale green, some gray- 

 ish, others brownish to black. There are four 

 rather large membranous, many-veined wings 

 without pattern, the hind wings being larger 



