The chromosomal relationships of Simulium arakawae, a black fly of medicalveterinary importance, are resolved relative to other members of the Simulium venustum species group and to the standard reference map for the subgenus Simulium. Simulium arakawae differs from the subgeneric standard by eight fixed inversions, apparently none of which are shared with any of the other 17 chromosomally studied nominal members of the group. The chromosomal features that indicate group membership might have been lost in S. arakawae, particularly if they were polymorphic in an ancestor.