THE HOUSE FLY. H 



NATURAL ENEMIES OF THE HOUSE FLY. 



The house fly has a number of natural enemies. The common 

 house centipede (fig. 12) destroys it in considerable numbers; there 

 is a small reddish mite which frequently covers its body and gradually 

 destroys it; it is subject to the attacks of four-winged wasplike para- 

 sites in its larva and pupa condition; and it is destroyed by predatory 

 beetles and ants at the same time. 



The most effective enemy of the house fly, however, is a fungous 

 disease,^ which carries off flies in large nmnbers, particularly toward 

 the close of the season. 



CONTROL MEASURES. 



THE USE OF SCREENS. 



A careful screening of windows and doors during the summer 

 months, with the supplementary use of sticky fly papers, is a pro- 

 tective measure against house flies known to everyone. As regards 

 screening it is only necessary here to emphasize the importance of 

 keeping food supplies screened or otherwise covered so that flies can 

 gain no access to them. This applies not only to homes, but also to 

 stores, restaurants, milk shops, and the like. Screening, of course, 

 will have no effect in decreasing the number of flies, but at least it 

 has the virtue of lessening the danger of contamination of food. 



FLY PAPERS AND POISONS. 



The use of sticky fly papers to destroy flies that have gained access 

 to houses is well known. Fly-poison preparations also are common. 

 Many of the commercial fly poisons contain arsenic, and their use in 

 the household is attended with considerable danger, especially to 

 children. This danger is lessened by the use of a weak solution of 

 formalin. A very effective fly poison is made by adding 3 teaspoon- 

 fuls of the commercial formalin to a pint of milk or water sweetened 

 with a little brown sugar. 



The United States Public Health Service recommends a 1 per cent 

 solution of sodium salicylate as almost equally effective. This is 

 prepared by dissolving 3 teaspoonfuls of the pure chemical (a pow- 

 der) in a pint of water, some brown sugar being added to render it 

 more attractive to flies. A convenient way of exposing these poisons 

 is by partly fiUing an ordinary drinking glass with the solution. A 

 saucer or plate is then lined with white blotting paper cut the size of 

 the dish and placed bottom up over the glass. The whole is then 

 quickly inverted and a small match stick placed under the edge of 

 the glass. As the solution evaporates from the paper more flows 

 out from the glass and thus the supply is automatically renewed. 



1 Empusa muscae. 



