This study of Simuliidae was carried out in the Whiteshell Forest Reserve and near La Salle, Manitoba in 1959 and 1960. The "helio-thermal" trap originally designed to capture Tabanidae (Thorsteinson, 1958) and improved by Bracken (1960) was further improved and used to monitor seasonal and diurnal activity of black flies and their response to motion. The diurnal activity of black flies was studied in relation to such meteorological factors as wind, light intensity, temperature, relative humidity and the time of day. It was found that flying conditions were optimal when it was calm or nearly so, cloudy with temperatures at about 70oF., and 75% relative humidities. On the average the greatest flying activity occurred between 7 and 9 in the morning. Seasonal activity was monitored by counting the black flies captured at two locations in two traps maintained from May to September, 1960. The peak of seasonal activity occurred on May 31 near La Salle and on June 15 in the Whiteshell Forest Reserve. The orientation to objects of various shapes and "degrees of brokenness" of contours was studied. It was found that black flies were attracted more to objects with solid contours. Black flies could recognize different shaped objects only by their differential "degree of brokenness" of contours. A stationary body suspended from underneath the trap increased the efficiency of the trap more than a moving body underneath the trap. Spheres were painted black, blue, red, yellow and green. It was found that the black, blue and red spheres attracted many more flies than the yellow and green ones. However when wooden sticks were painted various colours and placed into the current, the flies laid more eggs on the yellow and green sticks than on any of the others. Attempts were made to real black flies from the egg stage in the laboratory by means of artificially circulated and aerated water.