Octopus Uses Two Arms To 'Walk Away' From Trouble

Crissy Huffard, Robert Full and Farnis Barneka report this first scientific documentation of underwater "bipedal" locomotion of any animal in the March 25 issue of the journal Science.

Ordinarily, an octopus changes both its color and shape to evade predation. But when they use the familiar water propulsion to move quickly, they cannot maintain their stealth appearance. The authors postulate the two-armed behavior allows the octopus to slowly walk away from a predator while preserving its existing camouflage.

Robert Full, an animal locomotion expert, is supported through the National Science Foundation’s (NSF) Frontiers in Biological Research (FIBR) Program. Full postulates that sophisticated movements in animals are not under the control of the central nervous system. Rather, he asserts that reflexes or local nerve signals control these movements. In the case of the walking octopuses, groups of nerve cells in each arm control this sophisticated “fight-or-flight” motion.

While Crissy Huffard’s graduate work centers on the behavior of an Indonesian octopus, she recognized that her observations of the walking octopuses might help answer a different scientific question: how exactly do these animals move? This question connected her to Full, whose work emphasizes that the material properties of moving appendages strongly influence the mechanics of movement.

“One of the goals of the FIBR Program is to support the training of students who are fearless in working across disciplinary boundaries. This is an excellent case in point,” said Chris Greer, who manages the program for NSF. “Students like Crissy Huffard, who are willing and able to work across scientific boundaries, are a powerful force for removing perceived disciplinary barriers.”

Because octopuses lack bones, they do not have fixed hinges like the knees and ankles humans require for motion.Thus, they control water pressure in their soft appendages in ways that, while unknown, create remarkably complex movements. Full and Huffard continue to study this form of movement. The conclusions of the work will be extended to robotic theory, allowing the team to explore solutions for robot movement across varied or rough terrain.