24 INSECTS AND HUMAN WELFARE 



Alabama, and one western state, AYashington. The greater 

 uniformity tliroughoiit the year in New York, where the 

 opportunities lor fly-borne infection are curtailed, is very 

 marked. Another way in which the housefly can aid in the 

 spread of typhoid is through infecting milk on dairy farms 

 where carriers are present and ofl'er the flies a chance to be- 

 come infected. 



Flies are also responsible, and to a much greater extent, 

 for the i)revalence of infantile diarrhea or summer complaint, 

 and here their relation is very easily seen. 



Other activities of houseflies detrimental to public health 

 are of far less importance, but by no means negligible. They 

 can carry the eggs of parasitic worms as well as many bacteria 

 and other microorganisms present in the several types of un- 

 savory food upon which they feed indiscriminately. 



Recently much progress has been made in methods of 

 abating the housefly nuisance. It has been found by workers 

 in the Federal Department of Agriculture that certain sub- 

 stances, notably borax, hellebore, and a fertilizer consisting 

 of calcium cyanamid, acid phosphate and kainit, are highly 

 destructive to fly-larva^ in horse manure (whence the great 

 majority of our houseflies come) and that these substances 

 do not ruin the manure for agricultural purposes. Practical 

 traps whereby fly-larva^ in stored maniu'e may be caught and 

 destroyed before transformation have also been devised. 

 Richardson has shown that housefly larvae can develop only 

 in alkaline material, and some substances may thus be acidi- 

 fied to eliminate them as larval food. 



The people of the United States spend great sums of monej' 

 for fly-screens, fly-paper, fly-swatters and fly-traps and suf- 

 fer much sickness and death as a result of the ubiquitous 

 housefly. As j^et no great reduction of houseflies has been 

 accomplished, but the public regards them less and less as 

 harmless creatures, and should soon be in the proper mental 

 state to launch a decisive campaign against them. 



Cattle, horses, and other domestic animals, and more rarely 

 man himself, are troubled in nearly all parts of the world by a 



