The nocturnal swarming activity of the malaria mosquito: it’s not just the males

Background: Swarming is a key reproductive behaviour in Anopheles mosquitoes, yet several aspects of its spatiotemporal dynamics remain poorly understood. In particular, the period after sunset has received little attention due to limitations in field visibility and tracking resolution. Additionally, the role of females in swarm formation, and their positional fidelity to swarm-inducing markers, has been largely overlooked. Current studies mostly focus on male swarming behaviour and often ignore female contributions to swarm structure and maintenance. Addressing these gaps is essential to understand sex-specific behavioural patterns that shape malaria transmission dynamics. Methods: This study elucidates the swarming activity of virgin female and male Anopheles coluzzii under controlled laboratory conditions using infrared light-based three-dimensional tracking during and after sunset. Results: Our recordings reveal that both sexes engage in swarming, but females initiate swarming 14 s prior to males. During the peak swarming activity at sunset, females flew 31% faster than males (mean speeds of 0.67 m/s and 0.51 m/s, respectively), and females showed a broader dispersion in spatial positioning. Finally, females also maintain structured swarming activity for a longer period, up to at least one-hour after sunset. Despite these differences, both sexes formed aggregations directly above the visual swarm-inducing ground marker, suggesting shared spatial orientation mechanisms. Conclusions: These findings provide novel insights into the temporal persistence and structural features of female mosquito swarming, challenging traditional assumptions of male-dominated swarm behaviour and offering implications for future studies on vector ecology and control.