Nineteen species of immature simuliids (Diptera: Simuliidae) were collected from streams on Hardwicke Island in the Johnstone Straits of British Columbia. These species were Simulium aureum Fries, S. canadense Hearle, S. decorum Walker, S. hunteri Malloch, S. tuberosum Lundström complex, S. venustum Say – verecundum, Stone and Jamnback complex, Prosimulium dicum Dyar and Shannon, P. esselbaughi Sommerman, P. formosum Shewell, P. travisi Stone, Simulium anatinum Wood, S. bafftnense Twinn group, S. bicorne Dorogostajskij, Rubtzov and Vlasenko complex, S. gouldingi Stone, S. piperi Dyar and Shannon, S. pugetense (Dyar and Shannon), S. vernum Macquart complex, Prosimulium doveri Sommerman, and Stegopterna sp. Enderlein. The last nine species have not been reported previously from British Columbia. Species composition, succession, and seasonal abundance of larvae and pupae were determined from April to August of 1980 and 1981. Simulium venustum–verecundum complex and S. hunteri were the most abundant species in 1980, while S. hunteri and S. vernum complex were most abundant in 1981. Black fly productivity was greatly reduced in 1981.