Page:Popular Science Monthly Volume 79.djvu/147

Rh in these somewhat circumscribed settlements or "locations," they gave the impression that they were more numerous this year than last. In the sense that their numbers were more concentrated, owing to the limitation of moisture—a prime necessity in the life of a fly—this is probably true.

It may be of interest to consider some statistics, showing to what enormous numbers the descendants of one fly may reach in the course of a summer. As most of you are aware, the eggs of a house fly hatch in from approximately six to twelve hours, and the maggots issuing therefrom reach their full size in from four to seven days. The outer layers of their body then harden and turn brown, forming the puparium, while the parts within become what is known as the pupa. The duration of the pupal stage is from five to seven days, at the expiration of which time the adult emerges as a perfect fly. The life of the house fly then occupies from ten to twelve days, and there may be from ten to thirteen or more generations in a summer, depending upon the character of the season and on the latitude. Of the length of life of the adult we can not speak with certainty, for the only way this could be determined is by confining the insects, and when this is done, conditions of existence are so unnatural that observations upon this point are not reliable. A female house fly which has hibernated