124 



CALIFORNIA riRTT AND GAME 



in their distribution and actually far fewer of these are eaten, on the 

 average, than is generally supposed. In Califoi-nia, the large "salmon 

 fly," Ptcronarcifs ('(difornira (Fig. .'52), is ahuiuhnit in streams noi'th 

 of Lake Tahoe and in coastal streams north of San Francisco, but is 

 rare or absent in many of the drainage basins in the more southerly 

 portions of the Sierra Nevada Mountains, 



To attempt to introduce the large salmon fly, Pteronarcys into 

 streams where they are not now present, would probably prove to be 

 wasted effort by reason of the fact that being winged forms, they can, 

 and probably would, have distributed themselves before now had the 



Fig. 33. Mayfly nymph 

 Iron. Note gill-plates on 

 side of abdomen and de- 

 pre.ssed body and legs for 

 living in swift water. Six 

 times natural size. 



Fig. 3 4. Damselfly 

 nymph, Artjia. Note 

 three gill-plates on 

 end of abdomen. Three 

 times natural size. 



necessary environmental conditions that they require as home sites 

 existed therein. Further, every cold-water, unpolluted stream invari- 

 ably contains many smaller kinds of stonefly nymphs that are equally 

 as good food if not of as large size as Pteronarcys. 



Mayflies and stoneflies have similar life cycles. The eggs are laid 

 in the water where they hatch into nym])lis. Wlien grown they emerge 

 from the water as adults. They have no pupal stage. Mayfly nymphs 

 can always be recognized by the presence of gills on the back of the 

 abdomen (see Fig. 33). Xo other aquatic insect possesses gills in this 

 position. Stonefly nymphs are easily distinguished by their two tails 

 and tufts of filamentous gills at the bases of the legs. Many possess 



