i62 Arthropods as Simple Carriers of Disease 



parts of the country. Bishopp (1913) regards it as of much more 

 importance as a pest of domestic animals in the grain belt than else- 

 where in the United States. The life-history and habits of this 

 species have assumed a new significance since it has been suggested 

 that it may transmit the human diseases, infantile paralysis and 

 pellagra. In this country, the most detailed study of the fly is that 

 of Bishopp (19 1 3) whose data regarding the life cycle are as follows: 



The eggs like those of the house-fly,' are about one mm. 

 in length. Under a magnifying glass they show a distinct furrow 

 . along one side. When placed on any moist substance they hatch 

 in from one to three days after being deposited. 



The larvae or maggots (fig. 1 10) have the typical shape and actions 

 of most maggots of the Muscid group. They can be distinguished 

 from those of the house-fly as the stigma-plates are smaller, much 

 further apart, with the slits less sinuous. Development takes place 

 fairly rapidly when the proper food conditions are available and 

 the growth is completed within eleven to thirty or more days. 



The pupa (fig. no), like that of related flies, undergoes its develop- 

 ment within the contracted and hardened last larval skin, or pu- 

 parium. This is elongate oval, slightly thicker towards the head end, 

 and one-sixth to one-fourth of an inch in length. The pupal stage 

 requires six to twenty days, or in cool weather considerably longer. 



The life-cycle of the stable-fly is therefore considerably longer 

 than that of Musca domestica. Bishopp found that complete 

 development might be undergone in nineteen days, but that the 

 average period was somewhat longer, ranging from twenty-one to 

 twenty-five days, where conditions are very favorable. The longest 

 period which he observed was forty-three days, though his finding 

 of full grown larvae and pups in straw during the latter part of 

 March, in Northern Texas, showed that development may require 

 about three months, as he considered that these stages almost cer- 

 tainly developed from eggs deposited the previous December. 



The favorite breeding place, where available, seems to be straw or 

 manure mixed with straw. It also breeds in great numbers in horse- 

 manure, in company with Musca domestica. 



Newstead considers that in England the stable-fly hibernates in 

 the pupal stage. Bishopp finds that in the southern part of the 

 United States there is no true hibernation, as the adults have been 

 fovind to emerge at various times during the winter. He believes 

 that in the northern United States the winter is normally passed 



