Marine Vibrio swims in sea water by rotating a single, sheathed polar flagellum and swarms over viscous surfaces by numerous unsheathed lateral flagella, which are produced when cells are in viscous environment. Surprisingly, the motors of these flagella use different coupling ions for energy transduction: the energy source for the polar flagellar motor is the sodium-motive force, whereas the lateral flagellar motors are driven by the proton-motive force. Furthermore, the polar flagellum idiosyncratically functions as a tactile sensor controlling transcription of the genes for lateral flagella production by sensing viscous drag that restrict its movement.