Gait switching with phase reversal of locomotory waves in the centipede.

Crawling using locomotory waves is a common method of locomotion for limbless and many-legged invertebrates and stimulates the biomimetic engineering of flexible locomotion. It is generally believed that the direction of locomotory waves is fixed for a given species. However, we found that a centipede,, flexibly generated its gait to allow for locomotory waves that varied in direction, depending on (i) locomotion speed and (ii) the physical conditions of terrain. We also found a new type of centipede's swimming gait unlike eel-like way known so far which is using posteriorly traveling waves of horizontal body undulation. The gait patterns of the centipede were examined in various conditions and analyzed how the waves switched in detailed. We showed that gait patterns were associated with control of stride length rather than stride frequency. Discussion was made on a possible scenario of the gait transition in the centipede compatible with our observations. This finding may give a hint at bio-inspired control of flexible gait switching in response to irregular terrain.