64 



Insects and Disease 



hatch in from eight to twelve hours and the larvae 

 will become fully developed in from eight to four- 

 teen days. They then change to pupae (Fig. 50) 

 in which stage they may remain for another eight 

 to twenty days when the adult flies will emerge. 

 These figures must necessarily be indefinite be- 

 cause the weather and other conditions always 

 vary. Under the most favorable conditions of 

 moisture and temperature it is probably never less 

 than eight days from egg to adult fly and under 

 unfavorable conditions it may be as long as six 

 weeks. 



The larvae thrive best when the manure is kept 

 quite wet. I have often found them in almost 

 incredible numbers in stables that had not been 

 cleaned for some time. The horses standing there 

 at night added fresh material and kept it just wet 

 enough to make conditions almost ideal (Fig. 49). 



The pupae are usually found where the manure 

 is a little dryer, but it must not be too dry. When 

 the flies issue from the pupae they push their way 

 up to the surface where they remain for a short 

 time and allow the body to harden and the wings 

 to dry before they fly away to other manure or, 

 as too often happens, to some near-by kitchen or 

 restaurant or market place. 



Of course it is impossible for them to issue from 



