Stick Insect Locomotion on a Wheel: Patterns of Stopping and Starting

Abstract

The relationship between standing and steady walking was investigated for stick insects walking on a wheel. Normal hexapod coordination patterns ensure that each point in the gait cycle has static stability. Nevertheless, stick insects show preferred stopping sequences: the final protraction in ipsilateral metachronal sequences is most often by a front leg and least often by a rear leg (Fig. 1, Table 1). The associated preferred stance is one in which front, middle, and rear legs are spread apart (Fig. 2). This preferred stance does not conform precisely to those of steady walking, necessitating small adjustments to the walk in the final steps. First, the final leg protraction often occurs in the absence of strong retraction by the supporting legs. Second, the insect often takes advantage of the left/right asymmetry, letting rear and middle legs on the leading side retract beyond their normal endpoints while completing the metachronal sequence on the trailing side. Walking typically resumes with an initial retraction by all legs. Stances are close enough to leg configurations of steady walking that metachronal rhythms are often continuous across pauses, a feature which suggests that leg coordination is affected by peripheral parameters, such as leg position.