Rhythms of flight and ambulatory activity ofPlecia nearcticaHardy were determined by field observation and remote monitoring to be bimodal-diurnal. Light was not essential for mating in these insects, but they required light and an ambient temperature of at least 20°C for sustained flight. “Hovering flights” occurred early and late in the day; dispersal and “searching flights” occurred mainly during the afternoon. Feeding was necessary to the survival of field-collected adults in the laboratory. These males and females lived ca. 3 and 5 days, respectively. Periodicity was similar for both sexes, but males were the most active fliers.