240 THE HOUSE FLY DISEASE CARRIER 



the under side of leaves near the buildings. Specimens 

 of these fungus-infested flies were sent to Doctor Thax- 

 ter of Harvard University, and the organism that killed 

 them was found to be, not Empusa musca, as was 

 thought, but Empusa amcricana. 



THE BITING HOUSE FLY (Stomoxys calcitrant L.) 



This insect is rather closely related to the house fly 

 and greatly resembles it in appearance, in fact it is dif- 

 ficult to distinguish one from the other except by the 

 closest observation. Raillet has stated that the Sto- 

 moxys holds its head up while the house fly holds its 

 head down, but there are other ways of telling them 

 apart, as can be seen by comparing the illustrations of 

 the two species. The Stomoxys is of the same gray 

 color with dark lines, but its mouth parts are quite dif- 

 ferent; in fact a good way to distinguish between the 

 two flies is to allow them to walk over your hand ; if 

 it bites, Stomoxys; if it does not it is probably the 

 house fly. It is this other species about which we are 

 writing that gave rise to the old saying that flies begin 

 to bite before a rain, since the biting house fly is not 

 normally a house fly at all, but loves the out-of-doors. 



It has not yet and probably never will become as 

 truly a domestic species as Musca domestica. It is not 

 attracted to the garbage pail and the kitchen and din- 

 ing-room for food, but finds plenty of food on cattle 

 and horses and other domestic and also wild animals. 

 Under certain circumstances, however, it may become 

 a very common resident of houses. (Fig. 23.) 



