Unconventional lift-generating mechanisms in free-flying butterflies

Flying insects generate forces that are too large to be accounted for by conventional steady-state aerodynamics 1 , 2 . To investigate these mechanisms of force generation, we trained red admiral butterflies, Vanessa atalanta , to fly freely to and from artificial flowers in a wind tunnel, and used high-resolution, smoke-wire flow visualizations to obtain qualitative, high-speed digital images of the air flow around their wings. The images show that free-flying butterflies use a variety of unconventional aerodynamic mechanisms to generate force: wake capture 3 , two different types of leading-edge vortex 3 , 4 , 5 , 6 , 7 , active and inactive upstrokes 8 , in addition to the use of rotational mechanisms 3 and the Weis–Fogh ‘clap-and-fling’ mechanism 9 , 10 , 11 , 12 . Free-flying butterflies often used different aerodynamic mechanisms in successive strokes. There seems to be no one ‘key’ to insect flight, instead insects rely on a wide array of aerodynamic mechanisms to take off, manoeuvre, maintain steady flight, and for landing.