Six-legged-bound: a newly described insect gait.

Locomotor behaviour is a hallmark of animal biology and ecology. Mole crickets constitute a unique group of subterranean insects that present extreme morphological and behavioural adaptations. They therefore present a valuable model for locomotion-related research. Despite their remarkable leg-morphology adaptations, mole crickets mostly demonstrate the common insect double-tripod gait for locomotion. Here we report, however, that in response to an aversive stimulus from the front, the mole cricket will consistently adopt a unique backwards gait that we have termed 'backward-bound'. Our temporal and spatial analysis shows that this previously unreported six-legged gait comprises a cyclic alternation between the middle and hind-leg pairs with rarely observed (in insects) left-right in-phase synchronization, while the front legs display noisy and less-consistent phase dynamics. This exceptional gait is transient and is replaced by regular backwards walking after several cycles. It is employed to distance the animal quickly from danger. A gait that can be characterized as 'forward-bound' is also displayed by the mole cricket, albeit for a much shorter duration (up to two cycles).