Adult black flies were trapped at the townsite of Deep River from the early emergence of Prosimulium spp. (approx. 21 May) through to the late summer decline of Simulium spp. (in August). "Sticky" traps employing CO2 as an attractant were located at five sites throughout the town; in addition a trap was positioned at a "control" site outside the town limits near a heavily forested area. The overall numbers increased rapidly in early June, remaining at high levels until the first week in July, by which time over 110,000 flies had been captured. The numbers of flies recovered both within and outside the town fluctuated widely with weather conditions, seemingly influenced by precipitation. In the town, three centrally located traps captured only half as many adults as two traps near the southerly limits, where a small stream flowed through light forest. The control trap showed that black flies were at least 10 times more plentiful outside Deep River. Three insecticide applications did not have any measurable effect on fly numbers. The predominant local species is Simulium venustum Say.