Unlike the flight principles of conventional aircrafts,insects generate aerodynamic forces in an unsteady aerodynamics environment at low Reynolds number.Although both bird and insect flights are essentially based on flapping wings,there are important differences from each other.For most birds except hummingbird,useful aerodynamic forces are mostly produced during downstroke.On the other hand,insects produce lift and thrust during downstroke as well as during upstroke.Moreover,birds use stabilizers located at the tail to control and change their attitudes during flight.Insects change their attitudes by flapping their wings without any control surfaces at the tail.In addition,insects flap their wings with larger flapping angles at higher frequencies than birds.Insects also have ability to perform maneuverability at low flight speeds in confined spaces and remarkable hovering capability.