252 THE HOUSE FLY— DISEASE CARRIER 



apples and the refuse of cider mills and fermenting 

 vats of grape pomace. It is a rather rapid breeder, 

 and a generation may develop in twenty days, more or 

 less. It is attracted especially to preserves and canned 

 goods, and frequently damages raspberry vinegar. It 

 is often very difficult to prevent the fly from entering 

 fruit jars. 



There are about thirty species of Drosophila in 

 North America, and the majority of them breed in 

 the juices of decaying and fermenting fruit. Aside 

 from the one just mentioned, D. amoona, D. fimebris, 

 D. graminum, and D. transversa are occasionally found 

 in houses. Another species, D, cellaris, occurs in cel- 

 lars in fermenting liquids, such as wine, cider, vinegar, 

 and beer; also in decaying potatoes. Another species 

 damages flour paste ; and still another mustard pickles. 

 One species, D. Haveola, does not need decaying vege- 

 tation for its larval food, since its larvae mine the leaves 

 of cabbages and radishes. 



The fruit flies may be dangerous inhabitants of 

 houses, since they are nearly all attracted to excreta, 

 and some of them breed in human excrement. The 

 larva and puparium, as well as the adult fly of D. 

 ampelophila, are shown in Fig. 27. 



The Bluebottle or Greenbottle Flies 



The Blow Flies {Calliphora erythrocephala Meig., 



Lucilia ccosar L., Phormia terrcenovce Desv.) 



Several species of bluebottle or greenbottle flies oc- 

 casionally gain entrance to houses, and all are danger- 



