46 



ABTHBOPODA 



twice and attain full size in from four to eight days, 

 whereupon the outer skin hardens, swells out, and turns 

 brownish to form cases within which the pupae trans- 

 form in from four to eight days into the adults. 



If boards of health would compel the frequent removal 

 of horse manure from the vicinity of towns the fly nuisance 

 might be greatly abated. About one fifth of the soldiers 

 in the national encampment in 1898 developed typhoid 



FIG. 24. Common fly, its pupa, larva, and eggs. Photograph, twice 

 natural size. 



fever, which was undoubtedly transmitted in some cases 

 by flies. These insects visit unclean places and thus carry 

 the germs on their feet to distribute them later as they 

 walk about over our food. I have found more than a hun- 

 dred germs (bacteria) clinging to the feet of one fly. 



The house fly never bites, but before a rain the stable 

 fly (stomoxys), seen in large numbers on the cows, enters 

 the house and frequently bites human beings. Other 

 relatives of the house fly are the blowfly or blue-bottle 



