AQUATIC INSECTS OF FRESHWATER 



the adult, and the winged existence lasts but a few weeks; oviposition 

 being conducted by the same individual for a number of days. The 

 larvEe of the same brood also develop unequally, some growing so 



rapidly that they de- 

 vour their more tardy 

 brethren. -When cap- 

 tured, the nymphae 

 not only prey upon 

 each other but upon 

 any living thing kept 

 with them, and the 

 larvse and nymphse are 

 the most rapacious and 

 destructive enemies of 

 young fishes which the 

 aquariist encounters, a 

 single one often de- 

 stroying an entire hat- 

 ching of several hun- 

 dred young fishes in a 

 few days. Nor are 

 their attacks confined 

 to young fishes, what- 

 ever contains life is fair 

 game to them. The 

 principal famiHes of 

 the Atlantic Coast and 

 Gulf States are the 

 iEschinidas, Libell- 

 ulidse, CorduUidae, 

 Cordulegasteridse, Ag- 

 rionidae, Gomphidae; 

 and the Calepterygidae 

 or Damsel-flies, Fig. 

 216. The "Hammer- 

 headed dragon -flies" 

 comprise the genera 

 Agrion, Lestes and 

 Calopteryx, which frequent grassy margins of ponds, pools and swamps. 

 The larger are the "High-flying-dragon flies," j^schna and Corduligaster, 

 which frequent tall shrubbery and trees and are seldom seen over ponds 



FIG. 216. Dragon-flies. 

 ^ckna heros. 

 Libeilula pulchella. 

 Gomphus exi/is. 

 Argia -violacea, a Damsel-fly. 

 Reduced one-fourth. 



262 



