8 HOUSE FLIES. 
the germs of intestinal diseases such as typhoid fever and cholera 
from excreta to food supplies. It will also lay its eggs upon other 
decaying vegetable and animal material, but of the flies that infest 
dwelling houses, both in cities and on farms, a vast proportion comes 
from horse manure. 
It often happens, however, that this fly is very abundant in locali- 
ties where there is little or no horse 
manure, and in such cases it will be 
found breeding in other manure or 
in slops or fermenting vegetable 
material, such as spent hops, or 
bran, or ensilage. 
At Salem, Mass., Packard states 
that he reared a generation in 14 
days in horse manure. The dura- 
tion of the egg state was 24 hours, 
the larval state from 5 to 7 days, 
and the pupal state from 5 to 7 
days. At Washington the writer 
has found in midsummer that each 
Fic. 4—One of the blue-bottle flies (Phormia female lays at one time about 120 
pelle ae ay Saar (Authorsillus ees, which hatch in 8 hours, the 
larval period lasting 5.days and the 
pupal 5 days, making the total time for the development of the gen- 
eration 10 days. This was at the end of June. The periods of 
development vary with the climate and with the season, and the insect 
hibernates in the puparium condition in manure or at the surface of 
the ground under a manure heap. 
It also hibernates in houses as adult, 
hiding in crevices. 
The Washington observations in- 
dicate that the larvee molt twice, and 
that there are thus three distinct 
larval stages. 
The periods of development were 
found to be about as follows: Egg 
from deposition to hatching, one- 
third of a day; hatching of larva to 
first molt, 1 day; first to second 
molt, 1 day; second molt ‘to pupa- 
tion, 3 days; pupation to issuing of , Pace or aiaie tiene 
adult, 5 days; total life round, ap- 
proximately 10 days. There is thus abundance of time for the 
development of 12 or 13 generations in the climate of Washington 
every summer. 
459 
