AQUATIC INSECTS 



Nymphs. — Mayfly nymphs are of many shapes and sizes; 

 some have flattened heads and bodies and their sprawling 

 legs are held akimbo as in Heptagenia. Active runners, like 

 CallihcEtis, are set high on spindling legs, while the little 

 creeper, Leptophlehia, almost drags its low slung body. But 

 all mayfly nymphs agree in having seven pairs of gills on the 

 abdomen, and with rare exceptions have no gills anywhere 

 else. They have two or three long slender tail filaments,^ or 

 set£e, and but a single claw on each foot. Stonefly nymphs, 

 sometimes confused with mayflies, have two claws on each 

 foot and nearly all their gills are on the thorax. Their 

 differently shaped bodies reveal much about the places where 

 they live and their way of getting a living. Many are well 

 fitted for particular habitats but are helpless when they are 

 out of them. Epeorus (PL XV) is so flat and its gills and 

 claws such efficient hold-fasts that it can cling to a rock no 

 matter how strong the current, yet it is quite helpless among 

 slender plant stems where Callihatis is thoroughly at home 

 (Fig. 158). 



Adults. — Mayflies spend nearly all of their lives as nymphs 

 in the water. During this time they eat a great deal and in 

 a few weeks, or in the case of some species, in a year or more, 

 they emerge into the air as subimagos or "duns" with pale 

 gray wings (PL XI, i). Subimagos soon shed their skins 

 again and become fully matured imagos or "spinners" 

 (PL XI, 2). As winged insects their lives last only a few 

 hours or days at most, during which they do not eat at all. 

 For a long time the fishermen have called them "duns" 

 and "spinners." Fishermen of England have given them 

 other picture names, like "the silver gray," "the evening 

 spinner." Many of these fishermen have made their own 

 "dry flies," wrought of silk and fur and feathers like 

 those described in that most charming of guides, Ronald's 

 " Fly-Fisher's Entomology." 



Adult mayflies are delicately beautiful insects, soft gray, 



199 



