LIFE HISTORY 
21 
The rate of growth of the house fly larva varies ac¬ 
cording to temperature in much the same way as does 
the period of duration of the egg stage. In the writ¬ 
er’s original observations in midsummer in Washing¬ 
ton he found that the time from the hatching to the 
first molt was twenty-four hours; from the first molt to 
the second molt twenty-four hours; from the second 
molt to transformation to pupa seventy-two hours; mak¬ 
ing the duration of larval life five days. The larvae are 
very active and migrate from place to place in a ma¬ 
nure pile with facility. Mr. Newstead in Liverpool ob¬ 
served that they mature in the shortest period in fer¬ 
menting materials in a temperature of between 90° 
and 98° F., but that they usually leave the hotter por¬ 
tions of the stable manure when it reaches a temper¬ 
ature of from ioo° to no° F. At 54 0 F. the larval 
stage was considerably prolonged, and larvae kept at 
that temperature had not matured at the end of eight 
weeks. 
Doctor Hewitt at Manchester, England, showed that 
larvae of the first stage might molt as early as twenty 
hours after hatching, but that from twenty-four to 
thirty-six hours usually elapsed before the first molt. 
Under favorable conditions of temperature larvae in 
this stage remained three days without molting. In 
molting he noted that the skin was shed from the head 
and posteriorly, and that not only the skin was shed, 
but also the cephalopharyngeal sclerites, as well as the 
chitinous lining of the fore portion of the alimentary 
tract. He observed that the second stage of the larvae 
