THE STUDY OF DIPTERA 85 



THE STUDY OF DIPTERA. 

 By Percy H. GrIiMSHAw, F.R.S E., F.E.S. 



Of recent years a great impetus has been given to the study 

 of Diptera, or Two-winged FHes, by the discovery that many 

 of these insects play an important part in the dissemination 

 of disease. They may play the 7v/i? of intermediate host in 

 the life-cycle of some tiny protozoan which completes its 

 development within the body of man, and in so doing causes 

 a serious or fatal illness, or trhey may act as mere mechanical 

 carriers of disease-producing bacteria, conveying such 

 organisms from infected localities, and afterwards con- 

 taminating our food in such a way as to cause an outbreak 

 of the particular disease in a new area. The list of diseases 

 thus more or less directly due, not only in tropical climes 

 but also within our own country, to the agency of Diptera is 

 a long and formidable one. It is hardly necessary in this 

 place to trouble the reader with a list of such diseases ; the 

 mere mention of malaria, yellow fever, and sleeping-sickness 

 will be quite sufficient to convince him of the importance of 

 the subject to travellers abroad ; while within the limits of 

 the British Isles themselves, although the more formidable 

 diseases just mentioned are fortunately absent, yet it is now 

 a well-established fact that epidemic outbreaks of t)'phoid 

 fever, summer diarrhoea, diphtheria, smallpox, and other 

 ailments are largely due to the agenc}^ of the common House- 

 Fly, while certain other species are held to be more or less 

 responsible for the transmission of diseases of lesser import- 

 ance. 



In another way flies are injurious to the welfare of man- 

 kind, for many species destroy his growing crops : witness the 

 notorious Hessian Fly, devastator of wheat ; while other 

 groups, such as the Bot-Flies, attack his domestic animals, 

 injuring their health and seriously damaging the commercial 

 products derived from them. The annual loss due to 

 Dipterous agencies, indeed, is reckoned in millions of pounds 

 .sterling. 



