eeding ground in search of a favorable place in
which to pass the pupa stage. They will often congregate at the edges of
manure piles near the ground or burrow into the soil beneath, or they
may crawl considerable distances away from the pile to pupate in the
ground or in loose material under the edges of stones, boards, etc.

[Illustration: FIG. 6.--Larvae, or maggots, of the house fly. About
natural size. (Newstead.)]

The pupae (fig 7), or "sleepers," are more or less barrel shaped and dark
brown in color. In midsummer this stage usually lasts from 3 to 6 days.
The pupa stage is easily affected by temperature changes and may be
prolonged during hibernation for as long as 4 or 5 months. Numerous
rearing experiments in various parts of the country have shown that the
shortest time between the deposition of eggs and the emergence of the
adult fly is 8 days, and 10 and 12 day records were very common.

The adult fly, upon emerging from the puparium, works its way upward
through the soil or manure and upon reaching the air it crawls about
while its wings expand and the body hardens and assumes its normal
coloration. In from 2 1/2 to 20 days, as previously stated, the female
is ready to deposit eggs. As in the case of other periods of its life
history, so the preoviposition period is prolonged considerably by the
lower temperatures of spring and fall. In midsummer, with a
developmental period of from 8 to 10 days from egg to adult, and a
preoviposition period of from 3 to 4 days, a new generation would be
started every 11 to 14 days. Thus the climate of the District of
Columbia allows abundance of time for the development of from 10 to 12
generations every season.

[Illustration: FIG. 7.--Pupae of the house fly. About natural size.
(Newstead.)]

Flies usually remain near their breeding places if they have plenty of
food, but experiments recently made at Dallas, Tex., show that they may
migrate considerable distances; in fact, house flies, so marked that the
particular individuals could be identified, have been recaptured in
traps as far as 13 miles from the place where they were liberated.

HOW THE HOUSE FLY PASSES THE WINTER.

The prevailing opinion that the house fly lives through the winter as an
adult, hiding in cracks and crevices of buildings, etc., appears to be
erroneous. Under outdoor conditions house flies are killed during the
first really cold nights, that is, when the temperature falls to about