some modification of the anal organs. It is possible that the
captured fly serves as a nucleus to begin the balloon on. One
case of a captured fly but no balloon was observed. After
commencing, it is probable that the rest of the structure is made
by revolving the completed part between the hind legs and adding
more bubbles somewhat spirally. The posterior end of the balloon
is left more or less open. The purpose of this structure is to
attract the female. When numerous males were flying up and down
the road, it happened several times that a female was seen to
approach them from some choke-cherry blossoms near by. The males
immediately gathered in her path, and she with little hesitation
selected for a mate the one with the largest balloon, taking a
position _upon his back_. After copulation had begun, the pair
would settle down toward the ground, select a quiet spot, and the
female would alight by placing her front legs across a horizontal
grass blade, her head resting against the blade so as to brace
the body in position. Here she would continue to hold the male
beneath her for a little time, until the process was finished.
The male, meanwhile, would be rolling the balloon about in a
variety of positions, juggling with it, one might almost say.
After the male and female parted company, the male immediately
dropped the balloon upon the ground, and it was greedily seized
by ants. No illustration could properly show the beauty of the
balloon." (Aldrich and Turley, "A Balloon-making Fly," _American
Naturalist_, October, 1899.)

"In many species of moths the males 'assemble' around the freshly
emerged female, but no special advantage appears to attend on
early arrival. The female sits apparently motionless, while the
little crowd of suitors buzz around her for several minutes.