392 Annals Entomological Society of America [Vol. VI, 



V. MODIFICATIONS OF ADULT STRUCTURES. 



Reproduction is the sole end of the imago life. Parts 

 of the body which have no function connected with it are 

 reduced or atrophied. 



It is probable that, with but few exceptions, May-fiies 

 engage in some kind of mating flight. The character of this 

 flight and the time when it occurs vary. The following 

 records show some of these variations. On June 25th 

 a swarm of three or four hundred individuals of Choroterpes 

 basalis were swarming over the water of Fall Creek at about 

 four o'clock on a sunny afternoon. Their average rise must 

 have been thirty feet. From the swarm both males and females 

 were captured, but mating was not observed. On June 29th, 

 at 7:30 in the evening, a female Ephemera varia was captured 

 from a swarm which was rising and falling in flights of thirty 

 to forty feet. Often they descended to within five feet of the 

 ground. Their dance continued until darkness hid them. 

 Mating flights of Leptophlebia pr^epedita have been seen 

 in the middle of a sunny forenoon, and at two, four and five 

 o'clock of bright afternoons in May and June. None of these 

 rose higher than fifteen feet and two of the swarms did not 

 fiy more than six feet above the ground. One entire swarm 

 which was captured contained forty males and one female. 



Actual mating has been observed but a few times. The 

 most satisfactory observation was made in May, 1911, upon 

 a swarm of Bsetis, which were flying near Cascadilla Creek 

 just after a shower. Most of the time they were not flying 

 much above the level of the eye so that they could be clearly 

 seen. Large numbers continually settled on bushes and upon 

 my clothing, and there appeared to be about equal numbers 

 of males and females. Many matings occurred, but in only 

 seven could the positions of the insects be seen at all. The 

 male of one of the couples flew up and attached himself beneath 

 a female, pressed the dorsal side of his head against the ventral 

 side of her thorax and extended his fore-legs upward, in order 

 to clutch her prothorax. The setse of the female extended 

 straight out posteriorly, but those of the male were pointed 

 forward over his back so that their tips projected between 

 the heads of the two insects. The position of the abdomen 

 could not be clearly seen, but judging from that of the setse, it 



