Legged Locomotion in Lattices: Centipede Traversal of Obstacle-Rich Environments.

Centipedes locomote through complex obstacle-rich environments by propagating waves of body bending and limb stepping. However, little is known about how collisions with obstacles influence locomotion. In terrestrial environments such as branches or leaf litter, obstacles can both cause drag and offer affordances for the animals to generate thrust. In laboratory experiments, we challenged Scolopendra polymorpha (∼9 cm long, ∼1 cm wide) to negotiate model heterogeneous terrains, hexagonal and square lattices composed of thin posts. The centipedes maintained rapid motion (∼0.2 body lengths per cycle, comparable to flat ground speed) across lattices of different spacings by altering their body and limb postures in response to collisions. Several behaviors minimized deleterious limb and head collisions: the first was "prolonged limb adduction," in which consecutive limbs fold to the body after a leading limb collides with a post, while other limbs maintained a stepping pattern. The second, occurring in narrower lattices, was "body twisting," in which the animal propagated local body twists to locomote on its side using the posts as footholds. In some cases, the animals used a peristaltic-like gait, previously undocumented for this species. We propose that the principles discovered here can improve morphologies and control schemes for elongate robots tasked with navigating similar terradynamic scenarios.