larval food is considered. The eggs are deposited below the surface in
the cracks and interstices of the manure, several females usually
depositing in one spot, so that the eggs commonly are found in large
clusters (fig. 4) in selected places near the top of the pile, where a
high degree of heat is maintained by the fermentation below. The second
batch of eggs is laid from 8 to 10 days after the first. The eggs
usually hatch in less than 24 hours. Under the most favorable conditions
of temperature and moisture the egg state may last hardly more than 8
hours. The maggots which issue from the eggs are very small and
transparent. They grow rapidly, completing the growth of the larva stage
in three days under the most favorable conditions, although this stage
usually lasts from 4 to 7 days. The larval period may be prolonged
greatly by low temperature or by dryness or scarcity of the larval food.
As the larvæ (fig. 6) attain full size they gradually assume a creamy
white color. 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.--Larvæ, or maggots, of the house fly. About
natural size. (Newstead.)]

The pupæ (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