64 



NORTFI AMERICAN DIPTERA 



In addition to the irritation caused by their bites some members 

 of the family carry disease. In Africa OncJwcerciasis, a disease caused 

 by a worm {Onchocerca volvulus Leuckart) of the family Filariida? is 

 transmitted by EiisimuUum damnomm Theobald. In man the disease 

 takes the form of small to rather large, subcutaneous swellings and 

 may or may not be apparent without careful examination. From 40 to 

 50 per cent of the natives of Sierra Leone were said by Blacklock to be 

 infected in 1926.* 



* Ann. Trop. Med. & Parasit., xx. pp. 1-48. 203-218. 



I I ^ I f 





W W 



b 



J 



(a) pupa of Simulium venustum in pupal cocoon and 

 (b) pupa of S. bracteatum, with cocoon removed. (After 

 Metcalf and Sanderson). 



