Mechanics of a marine midge water locomotion

Marine midges, tiny insects with a body size of 2 mm and a weight of 0.07 dyn, provide valuable insights into advanced locomotion techniques. Found in shallow reefs at Wanlitong, Kenting National Park, Taiwan, these midges can continuously traverse seawater surfaces for over 90 min at speeds around 340 body-lengths per second. Their flight relies on two primary mechanisms: wing sculling to utilize surface tension for thrust and wing retraction to generate aerodynamic lift. This study addresses the gap in understanding how marine midges generate the lift and thrust needed for prolonged flight. We investigated their unique locomotion by conducting experiments to measure their weight, speed, and wing frequency. These measurements informed 3D computational fluid dynamics (CFD) simulations to analyze the aerodynamic forces involved. The results highlight the critical role of the ground effect, where maintaining minimal gaps of 0.08 mm between the midge trunk and 0.055 mm at the wing tips is essential for lift. Additionally, a high wing-beat frequency exceeding 300 Hz is crucial for generating sufficient lift during wing retraction. Our findings emphasize that ground effect, forward speed (>60 cm/s), and wing-beat frequency are key factors enabling marine midges to sustain flight above the sea surface. This unique adaptation for water surface locomotion not only showcases the midge's remarkable flight capabilities but also offers valuable insights for the design of micro-air vehicles (MAVs).