The ecology of Culicoides paraensis was studied with human bait collections at an agricultural research station near Belem and within 2 neighborhoods of Belem, Brazil, from 1977 to 1978. From collections conducted along transects that were centered on a house, we found most dense populations of host-seeking midges within and near the house. Host-seeking activity was least in areas fully exposed to sunlight compared to the levels of activity indoors and in shaded areas outside. Numbers of flies biting under shade trees and within the house increased during intervals of rain; concomitantly the levels of activity decreased in open areas. Seasonal population densities correlated with the pattern of rainfall, with a 2-month lag due to the long maturation time of immature C. paraensis. The effects of temperature and humidity on host-seeking activity are discussed.