The hybrids of three members of the viatica group of morabine grasshoppers from Kangaroo Island, South Australia, were studied. These members of the viatica group, which are primarily distinguished by their chromosome complements, have contiguous distributions. Grasshoppers collected from three narrow zones of overlap were studied cytologically. Breeding experiments were also conducted. The results of these studies indicate that a number of different factors contribute to the narrowness of the zones.