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 Qgg 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 100° to 110° F. At 54° 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 



