236 THE DRY-FLY MAN'S HANDBOOK 



may be a few hours (in some genera a few minutes) and 

 it may take some days, and these questions are difficult if 

 not impossible of solution from experiments with insects 

 in captivity, because when we place the Ephemeridae 

 among artificial surroundings they do not implicitly 

 follow the course pursued in a state of nature. 



When the fly has once assumed the imago dress 



the behaviour of the two sexes 

 Male imago. is in many ways diverse. The 



males congregate in great num- 

 bers, and are seen disporting themselves in the air, 

 sometimes at a great altitude, and at other times only 

 just above the bushes or trees at the river-bank. They 

 seem to be continuously engaged in an aimless dance, 

 rising swiftly and descending slowly. As soon as a 

 female imago leaves the shelter of the rushes or 

 boughs, the males in great numbers pursue her, two 

 or more seizing her from below and one coupling in 

 flight. The male then drops its wings, and the female 

 not being generally able to support the weight of both 

 with her wings, they descend, and by or before the 

 time when they reach the ground, the connection is 

 generally terminated. The male flies away to resume 

 with his companions the danse d' amour, and, being 

 addicted to polygamy, se,eks a second mate. 



After resting awhile, the female deposits her eggs in 



one of the ways previously 

 Female imago. described in this chapter. The 



eggs sink to the bed of the 

 river, hatch there in process of time, the nymph 



