Carbon dioxide-baited suction trap collections were related to simultaneous bait cattle collections of Culicoides variipennis sonorensis Wirth & Jones. Trap collections varied directly with numbers taken from each of 3 calves. More (3.4x) C. v. sonorensis were taken in a trap with 1,000 ml CO2/min versus a trap baited with approximately 300 ml/min (matched to calves by weight). Numbers of insects taken from three individual calves relative to their equivalent CO2 output did not differ, but engorgement of C. v. sonorensis was higher on 1 calf compared with the other 2 calves. Up to 281 C. v. sonorensis fed on a calf exposed for 10 min. More male (7.7x) and female (6.1x) C. v. sonorensis were collected from the calf relative to its equivalent amount of CO2. Under conditions described here, female C. v. sonorensis caught by a suction trap multiplied by 7.2 approximates numbers expected to be caught near a calf. Engorgement of C. v. sonorensis on individual calves declined as abundance increased. Culex quinquefasciatus Say was collected in equal numbers from the calves and their equivalent CO2 output, and none fed on the cattle. Most (85%) C. v. sonorensis in the vicinity of the CO2-baited suction trap were collected in the catch bag, compared with 26% of Cx. quinquefasciatus.