6 FARMERS’ BULLETIN 679. 
The number of eggs laid by an individual fly at one time is un- 
doubtedly large, probably averaging about 120, and as a single 
female will lay at least two and possibly four such batches, the 
enormous numbers in which the insects occur is thus plainly ac- 
counted for, especially when the abundance and universal occurrence 
of appropriate 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 are commonly 
found in large clusters in selected places near the top of the pile, 
rig, 9.—Eggs of the house fly. About natural size. (From Newstead.) 
where a high degree of heat is maintained by the fermentation below. 
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 eight hours. The maggots which issue from 
the eggs are very small and transparent. They grow rapidly and in 
the course of their development molt twice. There are thus three 
distinct larval stages, the duration of which is about as follows: 
(1) From hatching of the larva to first molt, one day; (2) first to 
second molt, one day; (3) second molt to pupation, two to three 
days, thus making the total length of the larval stage four to five 
days. This period may be greatly prolonged by low temperature or 
by dryness or scarcity.of the larval food. As the larve (fig. 11) 
