17 



forms, such as some Aqrionirhv, most of the y^sclniidit^ Lihc/- 

 Inla, Sf/iKpefrmii, and Mrsotlfen/is scatter widely inland. S//in- 

 petrum will be seen about fields and lawns, and the yEsclnikhe 

 in the vicinity of houses. 



FOOD RELATIONS. 



The nymphs are all predatory in habit. Most specie? 

 remain in ambush, aided by coverings of sand, mud, silt, and 

 algal growths, and by their own protective coloring, until their 

 prey wanders within reach. Anax jitn'nis and a few others 

 choose their prey. All capture it with a marvellously sudden 

 extension of the labium, bringing it into the grasp of the for- 

 midable lateral labial lobes. Almost all kinds of small aquatic 

 animals appear on the bill of fare of the group as a whole. 

 The Agyionida' have a seeming preference for EntoDiostraca 

 and May-fly nymphs. The vegetation-inhabiting species have 

 the most varied diet, including especially back-swimmers 

 {Notonecfa) and water-boatmen (C'o/v'^y/), small crustaceans, such 

 as Asellus and Allorchestes, thin-shelled mollusks, like Pfnjsa, 

 coleopterous and dipterous larvae, and even the younger or 

 weaker members of their own order. Anax takes even the 

 thicker-shelled univalves, like Atnnicola. The deep-water Epi- 

 cord'dia feeds principally on small mollusks, such as AnuiicoJa 

 and Phi/sa, as well as on other life of the bottom. The .Esr/i- 

 nidre, especially Anax, are most omnivorous creatures. The 

 larger odonate nymphs eat very young fish, and in some cases 

 appear to have caused a sweeping destruction of large numbers 

 of them. 



On the other hand, the nymphs are apparently eaten prin- 

 cipally by fishes and by one another ; hence their need for hid- 

 ing places in mud and sand or among matted vegetation. In 

 the course of Professor Forbes's studies of the food of fishes 

 ('88a, pp. 485, 524) he found odonate nymphs most abundant 

 (twenty-five per cent.) in the food of the grass pickerel [Esox 

 vermicalatm), and forming ten to thirteen per cent, of the food 

 of the crappie {Pomoxis annular id), the pirate perch {Apliredodenis 



