FIELD BOOK OF PONDS AND STREAMS 



water to explore the stones before she lays her eggs (p. 201). 

 One of these, Enallagma asperstim, observed by W. C. Woods, 

 stayed under water for twenty-five minutes. She wound her 

 wings around the abdomen, enclosing a blanket of air about 

 her, then walked down the stem of a plant and explored the 

 stream bottom for an area of two feet away. 



Nymphs. — Dragonfly nymphs usually require a long time to 

 mature ; thus Gomphus needs more than a year. On the other 

 hand certain damselflies such as Enallagma and Ischnura 

 may produce more than one brood in a season. Both dragon- 

 and damselflies usually pass the winter as nymphs in the mud 

 bottoms or in trash caught here and there in flowing streams 

 and begin to emerge late in the spring, leaving their cast- 

 off nymphal skins clinging to stems several inches above water. 

 A newly emerged dragonfly is soft-bodied and weak, and for 

 a little while after molting it can fly only haltingly if at all. 

 Dragonflies and damselflies spend most of their lives in the 

 water as nymphs and during that time they are the dominant 

 insect carnivores of the ponds, preying upon any animal 

 smaller than themselves. Although they can lunge and dodge 

 with lightning quickness their gait is usually slow and they 

 have a "stop, look and listen " way of moving over the bottom 



Fig. 160. — Dragonfly nymphs: i, with labium in 

 place; 2, with labium thrust forward as when 

 catching prey. 



214 



