Black Fly (species Simulium ) feeding on human blood. It does this by abrading the skin surface until a pool of blood forms, then it drinks it up. Black flies, which number about 100 species in Canada, occur in varying abundance in all parts of the country. Adult females feed on blood, causing irritation and discomfort to humans, domestic and wild mammals, and birds. Black flies cause economic losses through reduced beef and milk production, interference in recreation, reduced real estate values, and spread of diseases. In Canada black flies are known to transmit blood-borne parasites to turkeys, geese, and ducks.