A survey of crepuscular activities in Cordulia aenea was carried out at a site in north-western Germany (52.9° N) with an abundant population; this was during the optimal flight season, in favourable weather conditions under a clear sky. Diel activity commenced before sunrise and ceased after sunset. The species therefore belongs to the small group of species exhibiting both matutinal and vespertine activity. Activity during the diurnal period between dawn and dusk never ceased, resulting in a duration of daily flight activity of up to 17 h and 41 min in mid-June. In both twilight periods we predominantly saw patrolling males but also ovipositing females and formation of mating wheels. In the evening, males sometimes briefly interrupted their patrol flight for foraging and feeding. The primary utilization of dawn and dusk for reproductive activities, as occurred in C. aenea, is limited among European dragonflies to a small number of aeshnids and corduliids. A 24-hour rhythm of flight activity under the midnight sun, north of the Arctic Circle, is discussed.