FIELD BOOK OF PONDS AND STREAMS 



Associates. — IMayfly nymphs live upon food which is so 

 abundant that the snails and entomostracans and the few 

 herbivorous insects which share it with them in no way 

 menace their supply. Mayfly populations are not kept in 

 check by lack of food but by the animals which prey upon 

 them, these being almost ever>' carnivorous inhabitant of the 

 water, including dragonfly nymphs, water beetles, and young 

 fishes in enormous numbers. Alayflies are the most important 

 food of these 3^oung fishes and if some method of breeding 

 them in captivity could be discovered it would do much to 

 solve the food problems of fish hatcheries. 



Aquarium study and collecting. — Nymphs of quiet waters 

 are easily kept in aquaria supplied with algae and water plants. 

 If they are fullgrown they will shed their skins and usually 

 fly up to the nearest window-pane (Fig. 35). Either within 

 doors or in the streams, nymphs can be kept in cages till they 

 emerge as winged maj^flies. These life history cages are 

 elsewhere described. 



Identification. — Mayflies are divided into three subfamilies 

 which may be described, according to the nymphal habits of 

 their members, as the EphemerincB or burrowers (PL XIII), 

 BcEtina: or clamberers and runners (PI. XIV), and Hepta- 

 genince or flattened sprawlers (PI. XV). 



Burrowers or Ephemerinas, Hexagenia. — Hexagenias bur- 



1 JL 



Fig. 154. — Heads of two burrowing mayflies dis- 

 tinguishable by the shape of the rostrum (a): i, 

 Hexagenia; 2, Ephemera. The nvmphs are shown 

 in PL' XIII. 



204 



