A Study of Factors determining the Distribution of the Larvae of the Blackfly,Simulium ornatumMg

Field and laboratory studies on the rôle of oxygen concentration and speed of current on larvae ofSimulium ornatumMg. show that current speed is more important than oxygen concentration in governing their distribution. The larvae prefer waters with a velocity range of 50 to 120 cm./sec., the greatest numbers occurring between 80 and 90 cm./sec. Larvae move independently of oxygen in concentrations above 50 per cent, saturation level.