328 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 9 



Munson (1901)* concerning the typhoid epidemics of 1898 that ''where 

 a strong wind constantly blows from the same direction, a fly-borne 

 infection will extend down wind, as this insect always rises and gen- 

 erally moves in the direction of air currents." As is so often the case, 

 it is probable that these two diametrically opposed opinions may be 

 made to harmonize. Concerning flight across open country the evi- 

 dence presented is entirely in favor of the view that long distance 

 flights are common, especially up to distances of one-fourth to one- 

 half mile and longer distances are indicated by the observations of 

 Copeman, Howlett and Merriam and Hodge. Concerning distance 

 of flight under town and city conditions the evidence presented seems 

 to favor the view that where "food and shelter" are at hand disper- 

 sion is confined to within comparatively short distances of the breeding 

 place. Such is the opinion of Hine, Howard, Hewitt and Hindle, 

 though both Hewitt and Howard suggest the possibility of longer 

 flights. Cox, Lewis and Glynn (1912)^'' in discussing the possibiHty 

 of flies moving from one street or locality in a city to another make 

 the statement that "our observations, however, prove that such mi- 

 grations from one area to another do not occur to any extent." 



The total number of flies used in these several experiments to de- 

 termine the distance of dispersion would probably total less than 

 50,000, the work of Hindle accounting for more than one-half. All 

 work done then, and all the conclusions are based on a fewer number 

 of flies than would be expected to be produced during a season at 

 ^ny ordinary center of dispersal, such as a manure pile. 



It is fully apparent that these experiments and observations leave 

 much to be desired, especially from the standpoint of conditions in 

 Montana. On the data at hand it can be surmised that flight across 

 open country may be to considerable distances, but no limit of a 

 definite nature is given, if indeed it be possible to establish such. The 

 evidence presented concerning flight under city conditions is even less 

 conclusive ; a comparatively short radius of dispersion is indicated and 

 statements of conclusions are more or less definitely qualified, though 

 positive assertions, such as that of Cox, Lewis and Glynn are not 

 lacking. Suggestions as to factors influencing or determining the 

 radius and direction of dispersion are not few, but on the other 

 hand, they are neither convincing nor conclusive. The experiments 

 and results with which this paper deals concern an entire city and the 

 liberation of nearly 400,000 marked flies. This is about eight times 

 the total of all previous investigations combined and more than fif- 

 teen times as many as were used in the most extensive of these. 



