441 



are frequently found in the alimentary tract, but this is due to the fact 

 that other insects have been eaten which feed upon these organisms. 

 The following is a list of the kinds of food known to be eaten by 

 zygopterous nymphs. 



Protozoa Paramecium. 



Crustacea 



Copepoda . . . Cyclops. 

 Anemopoda . . . Daphnia. 



Arthropoda 



Arachnida . . . Hydrachnidae (rare). 



{Diptera — Chironomidae, Culicidae. 

 Odonata — Zygoptera. 

 Ephemerida — Ephemeridae. 



Vertebrata Very young fish. 



Color Adaptations. — In almost any collection of live zygopterous 

 nymphs, there will be found brown and green individuals of the same 

 species. When collected from localities with abundant green vegeta- 

 tion, nearly all the nymphs will be green ; when taken from situations 

 where little green vegetation occurs, the nymphs are brown or dark 

 in color. Furthermore, as has been observed in rearing specimens, 

 green nymphs placed in a jar without green plants become brown after 

 a few molts, and thus seem to be able to adapt themselves to the color 

 of the surroundings. The color of the nymph, contrary to what might 

 be expected, seems to have no influence upon the color of the adult. 



Bnemies. — The nymphs of Zygoptera are preyed upon by a number 

 of enemies, the most formidable of which are fishes. Forbes ('88) 

 reported that odonate nymphs formed ten to thirteen per cent, of the 

 food of Perca flavescens — the common perch, Aphredoderus sayanus 

 — the pirate perch, and Pomoxis annularis, the crappie ;and twenty-five 

 per cent, of the food of the grass pickerel, Bsox vcrmiculatiis. Riley 

 ('12) says that Lepomis gihbosus, a common sunfish, and the yellow 

 perch, Perca flavescens, commonly feed upon agrionid (coenagrionid) 

 nymphs. 



Among the predaceous aquatic Hemiptera, the genera Ranatra, 

 Belostoma, and Notonecta, and probably others, feed upon the nymphs. 



A mite, Arrhenurus sp., is a common external parasite of the 

 nymph. At the time of emergence of the adult, the mite migrates from 



