Fig. 47—Larva of house-fly.
LIFE-HISTORY AND HABITS
The eggs of the house-fly may be laid on almost any kind of decaying or fermenting material. If this is kept moist and a proper temperature maintained the larvæ or maggots ([Fig. 47]) that hatch from the eggs may develop. As a rule, however, these requirements are found only under certain conditions and are ordinarily found only in manure heaps or in privy vaults or latrines. All observers agree that the female fly prefers to deposit her eggs in horse manure when this can be found and when this is piled in heaps in the barn-yard ([Fig. 48]) or in the field the heat caused by the decay and fermentation makes ideal conditions for the development of the larvæ. Cow manure may serve as a breeding-place to a limited extent. The flies are immediately attracted to human excrement and breed freely in it when opportunity offers. Decaying vegetables or fruit, fermenting kitchen refuse and other materials sometimes also serve as breeding-places.
In suitable places in warm weather the eggs will hatch in from eight to twelve hours and the larvæ will become fully developed in from eight to fourteen days. They then change to pupæ ([Fig. 50]) in which stage they may remain for another eight to twenty days when the adult flies will emerge. These figures must necessarily be indefinite because the weather and other conditions always vary. Under the most favorable conditions of moisture and temperature it is probably never less than eight days from egg to adult fly and under unfavorable conditions it may be as long as six weeks.
The larvæ thrive best when the manure is kept quite wet. I have often found them in almost incredible numbers in stables that had not been cleaned for some time. The horses standing there at night added fresh material and kept it just wet enough to make conditions almost ideal ([Fig. 49]).
The pupæ are usually found where the manure is a little dryer, but it must not be too dry. When the flies issue from the pupæ they push their way up to the surface where they remain for a short time and allow the body to harden and the wings to dry before they fly away to other manure or, as too often happens, to some near-by kitchen or restaurant or market place.
