Tur CRANE-Furrs or New York — Part II 705 
the air and far overhead. A few were in copulation on the leaves, but 
from observations made later it seems probable that mating begins in 
the air and the united pair seek a support later on. Toward twilight 
the flies may be found in great numbers in company with many kinds of 
eaddice flies and may flies. The swarms vary in numbers from about 
fifty individuals to those including many thousands. Some of the larger 
of these swarms cover a vertical height of at least fifty feet, the lower 
individuals being about fifteen feet above the water. When danger 
approaches, the swarm either mounts into the air overhead or retreats 
before the breeze, never advancing nor moving sidewise. 
Out over the land in the smaller swarms, copulation was observed 
several times. The males in the swarm dart swiftly at the females and 
seize them almost instantly. They then usually leave the swarm and go 
sailing away, the male above doing the flying, the smaller female hanging 
limply beneath. The antennae of the male at this time are directed 
straight ahead and are slightly divergent, the legs hang downward, the 
wings vibrate rapidly. The female hangs downward with the legs trailing 
limply beneath, the wings nearly horizontal and motionless. The dead 
weight of the female continually pulls the male toward the water, and 
often both fall into the river. As a rule, copulation ends before the male 
is exhausted. The male opens his forceps and the female drops straight 
downward for a foot or so, quite like a parachute released from a balloon. 
If the pair are near the surface at the time of separation, the released 
female drops into the water. The male darts upward again and back 
into the swarm. The female slowly flies away, usually upstream but 
sometimes downstream, presumably to lay her eggs. She does not stop 
for swarms that she may encounter, and may even make a wide detour 
in order to avoid them. In a very few cases the female is the active 
partner and succeeds in pulling the male where she wills altho she is much 
smaller. No matings were observed during the hours of sunlight, and 
it was only at twilight or just after sunset that mating took place. Often 
a second male will seize a female already in copula and the three will 
come tumbling down into the water together. One such pairing of three 
individuals came down, and when they were about a foot above a board 
in the water the male in copulation dropped the other two. These rested 
for a moment, and then the remaining male attempted to engage the 
female in copulation. She resisted but finally he managed to seize her 
