AQUATIC INSECTS 



and brown, or pale and translucent, fragile and short-lived, 

 as their name, Ephemerida, implies. They have large front- 

 wings and small hind ones except in some very small species 

 such as Ccenis in which hind wings are altogether absent. 

 The adults have either two or three tail filaments, which are 

 much longer than those of the corresponding nymphs. Their 

 mouth parts are shrunken and useless; so that in the mayfly 

 countenance the whole mouth region is like a receding chin. 

 Their legs are weak and little used for walking, the front legs 

 of the males are long and often held forward with a reception- 

 line cordiality. Dr. J. G. Needham has aptly named one 

 mayfly the "white-gloved howdy" (Fig. 159). 



As soon as they emerge from the water the subimagos fly 

 upward to overhanging trees or shrubbery. They do not move 

 about very much until the mating flight which in some species 

 occurs almost immediately, in others within a day or two. 



The mating flight usually takes place in late afternoon or 

 twilight. Then hundreds of spinners, mostly males, swing 

 up and down through the air in a rhythmic dancing flight 

 over streams or lakes. With their rudder-like tails stiffly 

 extended they drop downward in swift descents of thirty 

 feet and more and then bound upward with the lightness of 

 springing thistledown. Hundreds or even thousands of 

 them move up and down together. In half ah hour they have 

 disappeared into the trees as suddenly as they came, or they 

 are strewn upon the water to become the food of eager fishes. 

 During this flight a dozen or so from the hundreds of males 

 mate with the few females which almost immediately lay 

 their eggs in the water and then die upon its surface. 



The little mayflies of the genus Bcetis fly in a low compact 

 mating swarm and the female literally climbs down into the 

 water to lay her eggs (PI. XII). The following description 

 is taken from my notes on her habits. 



Flying close to the surface of the water, the insect alighted 

 on a stone projecting slightly from the water and well pro- 



201 



