636 INSECT PESTS OF FARM, GARDEN AND ORCHARD 



is an object of suspicion in connection with any infectious 

 disease. The structure of the adult fly and its habits make it 

 more adaptable to the transmission of germ infections than 

 any other insect. It has hairs and bristles on mouth-parts 

 and feet which pick up filth or other matter. Secretions from the 

 mouth parts aid in the infection. 



Possibly the greatest danger of infection from flies is through 

 the milk supply, even though they frequent most other foods. 



Milk is an attractive food for 

 t flies and is also a very good 

 "^ culture medium for bacteria 

 so that infection in milk is 

 likely to develop more rapidly 

 than in other foods. And flies, 

 when they are permitted to 

 be, are always more numerous 

 about dairies and meat-mark- 

 ets than elsewhere. However, 

 it is not necessary here to build 

 up a case against the fly. The 

 foregoing remarks will serve 

 merely as a reminder of what 

 is already well-known. 



The fly breeds by preference 

 in horse manure but will also 

 breed in other kinds of man- 

 ure, in many kinds of filth and 

 garbage and even in human 

 excrement. It winters in the 

 larval and pupa stages and 

 There are many overlapping 



Fig. 546. Housefly above, the stable- 

 fly below, showing difference in 



mouth parts. 



probably also in the adult stage, 

 generations 'in the year, those late in the season being much larger 

 than the early ones because of the heavy mortality during the 

 winter months. The adults need no description. They are sim- 

 ilar to the stable-fly but differences in their mouth-parts illustrated 

 in the accompanying figure will readily separate them. 



It will be seen that the mouth-parts of the housefly are such 

 that it is unable to bite or puncture the skin. At times the house- 



