Observation on the distribution and seasonal variation of riverine tsetse population at Egbe in the Derived Savanna Zone of Nigeria was made and compared with variation in other vegetation types of the country. Egbe, in a sub-humid location, was observed to have a low rainy/high dry season population density similar to what occurs in part of the Southern Guinea Savanna Zone. To the north of these areas, the less humid vegetation zones show a definite reverse pattern (high rainy/low dry season) of seasonal population density. The Rain Forest Belt, a humid zone has, surprisingly, more similarity with the less humid zones to its far north than with the sub-humid zones nearer to it Irrespective of zone and season, a favourable temperature of between 26.1 and 26.7°C appeared important towards having a high population density. Reasons were given for the low rainy season tsetse density at Egbe. Unlike zones in the less humid north where rainy season dispersal is well marked, tsetse distribution in the Derived Savanna Zone remained by the riverine vegetation almost throughout the year. The advantage of this study to a proposed ranch for the area was highlighted.