Time series of the numbers of Simulium damnosum s.l. caught biting man each day at various locations in West Africa were investigated using auto-correlation methods and spectral analysis. After differencing the data sets up to the number of times for which significant partial autocorrelations were detected, significant peaks were found in the periodograms of the transformed series in 22 of the 23 series examined. The major peaks revealed the existence of cycles with periodicities of 2 to 3 days, which were interpreted as being indicative of gonotrophic cycle lengths. There was inconclusive evidence suggesting that the cycles for S. squamosum were slightly longer than those for S. damnosum s.str. and or S. sirbanum. One data set with associated parous rates was used to estimate a survival probability per oviposition cycle for S. damnosum/S. sirbanum of 0.46.