The distribution of Simulium damnosum theobald in Northern Nigeria

(1) This paper gives the results of a survey for the foci of Simulium damnosum in Northern Nigeria, accompanied by distribution maps. (2) A table of local native names for the fly is included. (3) Those negative areas which are, or may be assumed to be, free from S. damnosum ] are listed. (4) The distribution of the fly in relation to various environmental factors is discussed. Distribution is fixed primarily by the geology of the country, which determines the areas of suitable breeding rivers. Altitude, vegetation and climate appear to play less part in determining distribution, except that climatic factors may operate to prevent the fly from establishing itself in the far north. The absence of the fly from the far north is more certainly attributable to the absence of suitable breeding grounds. (5) S. damnosum is associated with areas of low to moderate population density ; all fly foci that have so far been surveyed for onchocerciasis have shown the presence of the disease.In Northern Nigeria onchocerciasis occurs even in the most northerly fly foci.