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 muscce, as was 
thought, but Empusa americana. 
The Biting House Fly (Stomoxys calcitrans 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.) 
