The effects of climate on the diurnal biting pattern of Simulium damnosum s.s. were measured at Jos Plateau, Nigeria. Rain in the hours prior to the catch inhibited morning activity by lowering the temperature and light intensity, and raising the humidity. Under shade there were no remarkable fluctuations in the light intensity, and no obvious peaks in activity; in sunny places, activity was bimodal, with a small morning peak and a pronounced afternoon one. The fastest changing climatic factor relative to an increase in the biting activity of flies was light intensity; followed by temperature.
