  At the millimeter scale and in the intermediate Reynolds number (Re) regime,
the midge and mosquito larvae can reach swimming speeds of more than one body
length per cycle performing a "figure-of-8" gait, in which their elongated
bodies periodically bend nearly into circles and then fully unfold. To
elucidate the propulsion mechanism of this cycle of motion, we conducted a 3D
numerical study which investigates the hydrodynamics of undergoing the
prescribed kinematics. Novel propulsion mechanisms, such as modulating the body
deformation rate to dynamically increase the maximum net propulsion force,
using asymmetric kinematics to generate torque and the appropriate rotation,
and controlling the radius of the curled body to manipulate the moment of
inertia. The figure-of-8 gait is found to achieve propulsion at a wide range of
Re, but is most effective at intermediate Re. The results were further
validated experimentally, via the development of a soft millimeter-sized robot
that can reach comparable speeds using the figure-of-8 gait.
