The nuptial dance of male mayflies helps avoid mistaken interception by other males

Male mayflies (Ephemeroptera) engage in oscillating nuptial flight patterns in which they climb vertically before passively parachuting downward. Males hold station above an area often in large numbers, intercepting adult females passing overhead. We reconstructed the flight behaviour of common mayfly (Ephemera vulgata) aggregations in 3D, while they were performing their nuptial dance and chasing artificial targets. Male mayflies chased any object that travelled horizontally above them and attempted to mate with it. Despite this indiscriminative chasing, we observed that male mayflies rarely caught each other by mistake. We suggest that the flight pattern of male mayflies helps them avoid each other whilst keeping the flight-motor system active. By flying vertically, males rarely fly horizontally above each other, the key signature used to identify potential mates. Male mayflies stop their pursuit if the target drops beneath the horizon. Therefore, we suggest that male mayflies engage in a downward parachute as an effective evasion strategy against other males that may aim to intercept them. During target interception, mayfly flight behaviour resembles the guidance law of proportional navigation. We found that mayflies selectively change speed, fanning their long posterior filaments and spreading their hindwings to decelerate before turning. Mayflies are more manoeuvrable at low speeds, and thus this deceleration prior to turns reduces overshooting and increases steering performance. Through simulation, we demonstrate that a speed-changing, mayfly-inspired proportional navigation controller is more effective than constant-speed models at staying below and colliding with manoeuvring targets.