text: Butterfly wings possess not only ultra-hydrophobic trait but also directional adhesive characteristics. If the water bead is along the radial outward (RO) direction from the body’s central axis, it rolls off and cleans the dirt away, leading to self-cleaning. On the other hand, if droplets stand against the opposite direction, they are pinned at the surface, leading adhesion and securing the flight stability of the butterfly by preventing deposit of dirt on the wings near the center of the body. SEM micrographs of wings exhibit hierarchy along the RO direction, arising from aligned microgrooves, covered by fine lamella-stacking nanostripes.