Fig. S3.

Drop motion on a single conical seta. When placed in fog, very tiny droplets (identified by numbers 1 and 2) could be condensed on the tip of seta (0 s). As water condensation continues, droplet 1 spontaneously rolled on a single conical seta from the tip to the base (0.163 s), and coalesced with droplet 2 to form larger water drops (droplet 1 + 2, 0.199 s). Similarly, this new larger drop could also move directionally to the base of setae (from 0.316 to 0.444 s), showing a self-propelled motion behavior.