A principle of visual attraction has been used in the design of mosquito traps for ecological studies. Tests in the field have shown that the design is efficient in capturing large numbers of mosquitoes in locations where ordinary light traps were unsatisfactory. Positive 24-hour attraction is achieved under naturally varying light conditions by using a black and white pattern that is superior in contrast to competing patterns in the environment. The sampling unit, in terms of air space, depends on the distance between contours in the pattern. Comparison with a suction trap under identical conditions show no significant differences in the ratio of empirically divided day to night catches. In very dark environments, a relatively uniform contrast in the pattern may be maintained between night and day with white light confined to the cylinder by collimators. Illumination in the yellow-red end of the spectrum reduces attraction to the pattern.