Investigations begun in 1947 in Saskatchewan have provided new data on the life-history and habits of the black fly Simulium arcticum Mall. The only published account of the biology and egg-laying habits of this species is that by Cameron (1922). He states that the eggs are laid in the usual black-fly fashion, i.e., attached in masses to rocks wetted by sprav in river rapids. The evidence here reported, however, indicates that the eggs are laid singly over the surface of flowing water and that these eggs settle and beconie embedded in the sand on the bottom. The investigations have conclusively shown that the species over-winters in the egg stage. These facts, important in an understanding of the biology of the species, are of particular value in planning a sound program of control.