204 



Aquatic Organisms 



antennae, will be sufficient for recognition of members 

 of this group. 



Stonefly nymphs are elongate and flattened, and very 

 similar to the adults in form of body. They possess 

 always a pair of tails at the end of the body. Most of 

 them have filamentous gills 

 underneath the body, tho a 

 few that live in well aerated 

 waters are lacking these. 

 The colors of the nymphs 

 are often livelier than those 

 of the adults, they being 

 adorned with bright greens 

 and yellows in ornate pat- 

 terns. 



The nymphs are mainly 

 carnivorous. They feed 

 upon mayfly nymphs and 

 midge larvas and many 

 other small animals occur- 

 ring in their haunts. 



One finds these nymphs 

 by lifting stones from water 

 where it runs swiftly, and 

 quickly inverting them. 

 The nymphs cling closely 

 to the under side of the 

 stones, lying flat with legs 

 outspread, and holding on 

 by means of stout paired 



claws that are like grappling hooks. Their legs are 

 flattened and laid down against the stone in such a 

 way that they offer little resistance to the passing 

 current. Stonefly nymphs are always found associated 

 with flat-bodied Mayfly nymphs of similar form, and 

 with greenish net-spinning caddis-worms. 



FIG. in. The nymph of a stone- 

 fly, Perla immarginata. 



(Photo by Lucy Wright Smith.) 



