The simuliid fauna of the Ethiopian region is notably isolated, only two of its species occurring elsewhere; the region has 124 described species, and others still undescribed. Simuliid larvae and pupae are adapted to attachment in moving water; adult females may disperse over considerable distances. This paper considers three examples of evident speciation in an ecological context:(1) speciation on afromontane ‘islands’ (2) theSimulium naeveigroup and the adaptive significance of the association between the early stages and freshwater crabs; (3) theS. damnosumcomplex, which includes the widespread vectors of human onchocerciasis. Maps show the distribution of species in these three gro