The principal species of stable fly on Zanzibar is Stomoxys nigra Marquart, which constitutes 90-98% of the Stomoxys spp. These flies are found in high concentrations in areas of the island that are heavily forested with poorly drained soils and in low concentrations in the sandy-coral coastal areas. Approximately 90% of S. nigra were caught in traps at 30 cm above the ground, and almost none were caught in traps above 1 m. This species was very active between 0600 and 0800 hours and again in late afternoon. More males than females were attracted to traps in the morning and late afternoon. Stable flies were found throughout the island and migrated distances up to 17 km or more. They moved along definite flyways such as roadways and drainage ditches, but not across open fields or through dense vegetation. At night, S. nigra adults rested on grass or in low shrubs. Dark-colored animals normally had higher numbers of flies than light-colored ones; however, there was great variability in attractivness to stable flies among animals of the same color.