NATURAL ENEMIES 69 



The only record of the attack of this species on 

 Musca domestica is by Brefeld. Empusa americana 

 seems confined to large flies, like the house fly, the 

 blow flies and the like. Doctor Thaxter states that it 

 is frequently met with from June to October on the 

 borders of woods near brooks or in shrubbery about 

 houses. The fly is generally found fixed to the under, 

 or rarely the upper, sides of leaves or bare twigs a few 

 feet above the ground. It occurs in New England and 

 North Carolina. The rhizoids or attaching hyphse, in- 

 stead of growing out in the form of numerous scat- 

 tered threads, are developed in an even layer around the 

 insect's body, forming with the conidiophores a con- 

 tinuous mat-like covering, which often becomes dark 

 rust colored on exposure to the weather. 



These are, so far as known, the only true botanical 

 enemies of the house fly. Of course, breeding as it 

 does in fermenting organic matter and in the dirtiest 

 and filthiest locations, and frequenting such situations 

 as it does in search of food, it carries upon its body, 

 and within its alimentary canal for the brief period 

 which it takes for its food to pass through, any num- 

 ber of spores of fungi and of bacteria, but it is prob- 

 able that nearly all of these are carried accidentally 

 by the fly and do it no harm. Many species of many 

 genera of fungi and bacteria have been cultivated upon 

 sterilized plates upon which flies caught haphazard 

 have been allowed to walk and which they have been 

 allowed to speck, but as just stated these are probably 

 innoxious to the fly itself. From the observations of 



