LIFE HISTORY 39 



with such possibiHties of multiplication ; but it must be 

 remembered that in the supposed instance upon which 

 we have figured, all of the eggs hatched and all of the 

 progeny have survived, whereas in nature a fly has 

 many chances of death, not only between the egg and 

 the adult, but as an adult before the period of sexual 

 maturity has been reached. And it is upon this period 

 which must elapse between the issuing of a fly and the 

 time w^hen it shall lay eggs that one of the several ex- 

 cellent plans for the warfare against this species has 

 been based. It must be remembered, on the other hand, 

 that in the table we have assumed that each female 

 has laid only 120 eggs, that is one batch, while in 

 reality she may lay four such batches. The task of 

 estimating the possibilities on the larger basis is left 

 to some reader who likes to multiply. Does not a con- 

 templation of these possibilities, even with all the pos- 

 sible accidents of nature to limit them, indicate in the 

 strongest possible way, even if the carriage of disease 

 by these pernicious creatures were not considered, the 

 necessity of an effort on the part of people to assist 

 nature in limiting a nuisance to humanity? 



Number by Actual Count in Relation to 

 Quantity of Food 



On August 9th in Washington a quarter of a pound 

 of rather well -infested horse manure was taken from a 

 manure pile, and in it were counted 160 larvae and 146 

 puparia. This would make about 1,200 house flies to 

 the pound of manure. This, however, cannot be taken 



