The House-fly as a Carrier of Disease 14,5 



necessary that we define what is meant by "house-fly" and that we 

 then consider the life-history of the insect. 



There are many flies which are occasionally to be found in houses, 

 but according to various counts, from 95 per cent to 99 per cent of 

 these in warm weather in the Eastern United States belong to the 

 one species Musca domesiica (fig. 108). This is the dominant house- 

 fly the world over and is the one which merits the name. It has been 

 well characterized by Schiner (1864), whose description has been 

 freely translated by Hewitt, as follows : 



" Frons of male occup5dng a fourth part of the breadth of the head. 

 Frontal stripe of female narrow in front, so broad behind that it 

 entirely fiUs up the width of the frons. The dorsal region of the 

 thorax dusty grey in color with four equally broad longitudinal 

 stripes. ScuteUum gray with black sides. The light regions of 

 the abdomen yellowish, transparent, the darkest parts at least at 

 the base of the ventral side yellow. The last segment and a dorsal 

 line blackish brown. Seen from behind and against the light, the 

 whole abdomen shimmering yellow, and only on each side of the 

 dorsal line on each segment a dull transverse band. The lower part 

 of the face silky yellow, shot with blackish brown. Median stripe 

 velvety black. Antennas brown. Palpi black. Legs blackish 

 brown. Wings tinged with pale gray with yellowish base. The 

 female has a broad velvety back, often reddishly shimmering frontal 

 stripe, which is not broader at the anterior end than at the bases of 

 the antennae, but become so very much broader above that the Hght 

 dustiness of the sides is entirely obliterated. The abdomen gradu- 

 ally becoming darker. The shimmering areas on the separate seg- 

 ments generally brownish. AU the other parts are the same as in 

 the male." 



The other species of flies found in houses in the Eastern United 

 States which are frequently mistaken for the house or typhoid fly 

 may readily be distinguished by the characters of the following key : 



a. Apical cell (Rg) of the wide wing open, i.e., the bounding veins 

 parallel or divergent (fig. 100). Their larvas are flattened, the 

 intermediate body segments each fringed with fleshy, more or 

 less spinose, processes Fannia 



b. Male with the sides of the second and third abdominal seg- 

 ments translucent yellowish. The larva with three pairs 

 of nearly equal spiniferous appendages on each segment, 



