3D underwater swimming kinematics in aquatic insects

Multimodality (i.e., efficient travel across aerial, terrestrial, and/or aquatic domains) is a common quality among animals but is difficult to build into engineered devices. Many insect species are especially adept at multimodal movement and could potentially serve as a model for new bioinspired vehicles or other technology; however, our understanding of the physical mechanisms underpinning their abilities is limited. Here we investigate the swimming behavior of three distinct insect families that regularly locomote across and between air, water, and land: water boatmen (Corixidae), backswimmers (Notonectidae), and diving beetles (Dytiscidae). In each of these insects, swimming is primarily driven by a pair of elongated, bristled hind legs that row like paddles, with a distinct power-recovery cycle; during the power stroke, the bristles are extended, and during the recovery stroke they collapse (increasing and decreasing, respectively, the effective area of the paddle). We qualitatively compare the paddle kinematics and overall swimming trajectory/speed between these three insects to identify similarities and differences in swimming patterns. Our results carry implications for both fundamental biology and the potential for bioinspired design; they will serve as a baseline for future work exploring the forces generated by bristled appendages in the context of underwater locomotion.