A few hours before pupation they become very restless and
migrate from their feeding 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.
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