Data and code from: The complex swarming dynamics of malaria mosquitoes emerge from simple minimally-interactive behavioral rules

Many insect species exhibit swarming behavior, often to reproduce. In such mating swarms, tens to thousands of male insects congregate near a visual ground marker, and females join for in-flight mating. Despite its importance for reproduction and survival, the biology and physics of insect swarming remains poorly understood. In particular, it is unclear whether swarming insects follow similar highly interactive behavioral rules as flocking birds and schooling fish. In flocking and schooling, neighbors exhibit strong mutual attraction, alignment, and collision avoidance. Here, we combined high-speed videography-based experiments with agent-based modeling to study the mating swarms of male malaria mosquitoes at sunset. By video-tracking the three-dimensional flight kinematics of swarming mosquitoes, we revealed that these animals exhibited highly stereotypic flight behaviors. Swarming mosquitoes tend to fly straight across the swarm center, and perform sharp saccadic turns at the swarm boundaries. Based on these observations, we derived parsimonious behavioral rules for swarming: for flight path alignment and swarm centering, mosquitoes rely on visual cues of the ground marker and sunset; and interactions between conspecifics only occur at very short distances, to avoid collisions. Using agent-based modelling and systematic simulations, we showed that this small set of behavioral rules is both necessary and sufficient to reproduce the complex emergent flight kinematics and coordinated patterns observed in real swarms. This suggests that, unlike highly interactive bird flocking and fish schooling, insect swarming may be primarily driven by responses to environmental cues instead of mutual interactions.