18 PROCEEDINGS ENTOMOLOGICAL SOCIETY 



Second Vice-President, Mr. Frederick Knab; Recording Secretary, 

 Mr. A. B. Gahan; Editor, Mr. J. C. Crawford; Corresponding 

 Secretary-Treasurer, Mr. S. A. Rohwer; members of the Execu- 

 tive Committee at Large, Mr. A. L. Quaintance, Mr. E. A. Schwarz 

 and Mr. W. D. Hunter. 



For Vice-President of the Washington Academy of Sciences Mr. 

 W. D. Hunter was renominated. 



Under the head of Program the following papers were pre- 

 sented : 



NON -INTENTIONAL DISPERSAL OF MUSCOID SPECIES BY MAN, 

 WITH PARTICULAR REFERENCE TO TACHINID SPECIES. 



BY CHARLES H. T. TOWNSEND, 

 Bureau of Entomology, U. 8. Department of Agriculture. 



Setting out with the statement that we are considering only 

 species which have access to ships lying in port in the country of 

 origin, either coming aboard by their own locomotion or being 

 brought aboard by man in material for shipment, we find that just 

 two sets of conditions are necessary for effective dispersal to new 

 countries : 



(1) The conditions under which a given species normally breeds, 

 or lives in either a quiescent or active state, must be maintained 

 on shipboard in transit between the country of origin and the 

 country of introduction. 



(2) The same conditions must be at hand in the country of 

 introduction immediately upon arrival of the species, in order that 

 it may establish and maintain itself. 



The muscoid species whose maggots normally live in the dung 

 of domestic animals are easily carried to all parts of the world 

 where cattle and like animals are shipped. Such are Promusca 

 domestica, Stomoxys calcitrans, Haematobia irritans, Mnscina 

 stabulans, Musca vomitoria and erythrocephala, Ludlia caesar and 

 sericata, etc. Both sets of conditions are present in these cases. 



Contrasted with these are the cases of the screw-worm fty, 

 Cochliomyia macellaria, whose maggots live in open sores of ani- 

 mals and in fresh carcases; and Cynomya mortuorum, whose mag- 

 gots infest older carcases. While the second set of conditions may 

 be present quite commonly in these cases, the first is practically 

 always lacking. Hence these species are not spread. The first 

 is confined to America, and has never been turned up elsewhere. 



