theless, when confined in the warm season of tlie year to a small re- 

 ceptacle, not at all tenacious of life. It results from this fact, for 

 example, that it is almost impossible to ascertain the leniith of the 

 life of the house fly in the adult condition. These breeding experi- 

 ments in confinement showed that the house fly will lay its eggs freely 

 on fresh horse manure in an undisturbed condition. When the ma- 

 nure is spread out the flies will not lay their eggs on it. They can 

 very rarely be induced to lay their eggs upon anything but horse 

 manure and cow manure, and their preference for the former is very 

 marked. Although eggs were laid upon cow manure, the larvse 



were unable to mature in this 

 substance. The experiments, 

 in fact, indicated that horse 

 manure is by far the most 

 favored breeding place of this 

 species. 



Continuous observations in- 

 dicated that the larva> molt 

 twice, and that there are thus 

 three distinct larval stages. 

 The periods of development 

 were found to be about as fol- 

 lows: Egg from deposition to 

 hatching, one-third of a day; 

 hatching of larva to first molt, 

 one day ; first to second molt, 

 one day; second molt to pupa- 



FlG. 4.— The green bottle fly (LitclUa cn'sar): a, i- fU«p„ /^Lia-g- i^iii->.if imi i.^ 



adult? 6, head from front; c, antenna— all enlarged tlOn, inrec (la^S, pupaiion lO 

 (from Ann. Kept. U. S. Dept. Agrie., 1890). issuing of the adult, five daVS : 



total life round, approximately 

 ten days. There is thus abundance of time for the development of 

 twelve or thirteen generations in the climate of Washington every 

 summer. 



The number of eggs laid by an individual fly is undoubtedly large, 

 averaging about li20, and the enormous numbers in which the insects 

 occur is thus plainly accounted for, especially when we consider the 

 abundance and universal occurrence of appropriate larval food. In 

 order to ascertain the numbers in wdiich house fly larva^ occur in horse 

 manure piles, a quarter of a pound of rather well-infested horse ma- 

 nure was taken on August 0, and in it were counted 100 larva^ and 14(i 

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

 manure. This, however, can not be taken as an average, since no larvje 

 are found in perhaps the greater part of ordinary horse manure jjiles. 

 Neither, however, does it show the limit of what can be found, since 

 about 200 puparia were found in less than 1 cubic inch of manure taken 

 from a spot 2 inches below the surface of the pile where the larva? had 



ICir. :55] 



