A cattle-baited (C-B) trap and a Trueman–McIver (T-M) segregating CO2 trap provided information on seasonal abundance, host-seeking activity, and blood-feeding of biting-flies near St. John's, Newfoundland. A total of 19 682 biting-flies (26 species) were collected (C-B trap = 11 407; T-M trap = 8275) from 26 May to 16 September 1982. Black-flies (Simuliidae) comprised 94.1% of the total sample (C-B trap = 10 747; T-M trap = 7773). Mosquitoes (Culicidae), biting midges (Ceratopogonidae), and tabanids (Tabanidae) comprised the remainder. Blood-fed flies represented 54.7% of the total catch in the C-B trap, but the proportion varied considerably among species. Black-fly activity was concentrated in June and July, though flies were also collected in May, August, and September. Prosimulium mixtum was the predominant species in June and Simulium venustum/verecundum complex was the major pest in July. Prosimulium mixtum was most active from mid-morning to late-afternoon, with little evening activity. Simulium venustum/verecundum complex showed 2 peaks of activity, one in the morning and another in the early evening. A few P. mixtum and S. venustum/verecundum complex were active after dark. Captures from the T-M and C-B traps were compared to test the reliability of the T-M trap as an indicator of activity of biting-flies attracted to cattle. Significant correlations (P < 0.001) between the number of flies collected in the 2 traps were found for P. mixtum and S. venustum/verecundum complex. Remaining species were taken in numbers too low for analysis.