280 ORDER DIPTERA 



It was first noticed as troublesome to cattle in this country 

 in 1887, and while we cannot say with certainty just when 

 it was introduced, we may be pretty sure that it was during 

 the year 1886, or at most not earlier than 1885. It is even 

 possible that it may have been brought over in the spring of 

 1887, as its powers of reproduction are such that a few weeks 

 would suffice to make it a conspicuous pest in a limited 

 area. 



Within two years from the time it was first recognized in 

 serious numbers it had become so numerous and had spread 

 over so large a region that it was made the subject of a 

 very careful and successful study by Messrs. Howard and 

 Marlatt of the Division of Entomology. The results of 

 these investigations were published in Insect Life (vol. ii, p. 

 93) and in the Annual Report of the Commissioner of Agri- 

 culture for 1889. 



As to its introduction and spread in America, all accounts 

 agree in placing the first serious occurrence of this insect in 

 the vicinity of Philadelphia, and it appears probable that 

 it was at that port that the flies first landed. 



From there as a centre it spread in all directions, though 

 at first mainly southward, and by 1889 it had covered most 

 of the State of New Jersey, portions of eastern Pennsylvania, 

 a considerable area in Maryland, and also a portion of 

 northern Virginia. 



In 1891 it had been reported from New York, Ohio, Ken- 

 tucky, Georgia, Florida, and Mississippi, and in 1892 from 

 Connecticut, Massachusetts, Canada, Michigan, Indiana, 

 Iowa, Louisiana, and Texas. 



The adults of the horn fly are about half as large as the 

 common house fly and very much like it in shape and color. 

 The accompanying figures will serve to distinguish it. The 

 larval stages are passed in from four to six days. 



The pupa stage may last from five to eight or ten days, so 

 that the full time from egg deposition varies from ten to 

 seventeen days, estimated for the average as about two weeks. 

 As the flies doubtless begin laying soon after issuing from 

 the pupa stage, there is room for a number of generations 



