AQUATIC INSECTS 



tected from the force of the current on its downstream side. 

 She at once walked to the protected side and downward to 

 the water. First, wrapping her wings about her abdomen, 

 she made several attempts to immerse her head and thorax. 

 This appears to be the critical stage in the performance, and 

 many mayflies are washed away while attempting it. Once 

 under the water she started on a tour of inspection. This 

 lasted for several minutes during which she continually 

 walked to and fro, pausing, feeling the stone with the tip of 

 her abdomen, and passing on unsatisfied. When she finally 

 found a suitable place she braced her legs firmly, bending the 

 end of her abdomen downward and her tail filaments upward. 

 She then began swinging her whole abdomen from side to 

 side with a slow pendulum-like motion, at each stroke leaving 

 an irregular row of minute white eggs adhering to the surface, 

 the first ones circular and somewhat longer than those which 

 came later. As the egg mass grew larger she moved forward 

 a little to allow the eggs to lie in succeeding rows. When her 

 supply was exhausted she jerked her abdomen upward and 

 abruptly clambered out of the water. 



Habitat and season. — Mayfly nymphs live in clean fresh 

 waters, flowing rivulets or rivers, tumbling waterfalls or quiet 

 pools; they -have become adapted to every aquatic situation 

 except foul water (PI. III). In many ponds they far out- 

 number all other animals anywhere near their equal in size. 



Spring is the mayfly season and the fullgroWn nymphs with 

 their black wing-pads are abundant from March to late June 

 and adults are emerging and swarming at this time. Young 

 nymphs can be found in shallow brooks the year around. 



Food. — These nymphs are confirmed vegetarians; their 

 staple food is the great crop of diatoms and desmids which 

 makes the golden-green color upon stones of the brook bottom 

 and covers almost every object in the water (PL IV). Be- 

 sides this they eat the soft tissues of larger plants either living 

 or dead. 



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