Abstract
The onchocerciasis is one of the most important diseases of human in Ethiopia. From the epidemiological point of view there is apparently much remained to be investigated on the ecology of the vector, the black flies. In this study the biting habit of the black fly, Simulium damnosum, against man was observed particularly on the diurnal fluctuation of the biting activity. The biting collections were carried out in two types of places, namely the sunny places and the shady places. It was noticed that in the sunny places the flies began to come attacking man with the rise in temperature and illumination intensity in the morning but then the number of flies decreased according to the sudden increase in the intensity of illumination. So there appeared a peak in the activity around 9 : 00 hours a.m. There was also a peak observed in the afternoon at about 5 : 00p.m. It can be concluded that the biting activity of this fly has a bipeaked fluctuation picture in the daytime, one peak in the morning and another in the afternoon. However in the shady places where no remarkable fluctuation in the illumination intensity occurred no obvious peaks in the activity could be observed.
