144 Annals Entomological Society of America  [Vol. VII, 
6th. Adults were very abundant during August 1-6, and 
it was a common thing to find numbers of them copulating. 
Local distribution—In spite of the fact that these insects 
have well developed powers of flight they are not found at 
any great distance from the waterlilies. They occurred 
ordinarily on the leaves and flowers of these plants and when 
disturbed made only short flights, seldom taking to open 
water or to shore. Only in rare instances were flies found 
resting on plants other than N. americana. When undisturbed 
they assembled in the open flowers or ran restlessly about 
over the lily leaves, making short flights where leaves were not 
contiguous. 
Relation to water.—These flies are related to the water 
in several interesting ways. Although the emergence of the 
adult has not been observed in the field it seems safe to assume 
that when the adult emerges from the pupal stage it must of 
necessity push the window open and pass up through the water 
to the surface, either by crawling up the petiole, or by inde- 
pendent passage through the water, presumably the former. 
It was found that the flies emerged and came to the surface 
when the infested petioles of N. americana were brought into 
the laboratory and completely submerged in water. In many 
cases individuals which develop near the base of the longer 
petioles must, in emerging, come up through about five feet 
of water before reaching the surface. 
It seems almost certain that the female deposits the eggs 
by going into the water and crawling down the petiole to the 
place where the eggs are deposited. Careful watch was kept 
on adults for periods of an hour or more at a time and none 
were observed to go beneath the surface in open water. If 
perchance an individual did alight on the surface it immediately 
took to wing again. Adults which fell on the surface of the 
water did not sink, but appeared to be supported mainly by 
the surface film. The fact that they may and do voluntarily 
pass under water was demonstrated when the writer observed 
a few individuals walk over the edge of the lily leaf, go under 
water, and travel on the lower surface of the leaf for short 
distances. None were seen to go down the petiole. 
Experiments in which adults were submerged showed that 
under such conditions the flies apparently have a specific 
gravity less than water, and consequently they rise to the 
