Study finds octopuses use front arms to explore, back arms for locomotion

Scientists analyzing years of underwater footage report that octopuses do not favor a single dominant arm the way many humans favor a hand, but they do tend to use their front limbs more often for exploration while reserving rear limbs for movement.

Researchers reviewed short videos of wild octopuses crawling, swimming, standing, fetching and groping and tracked how each of the eight arms was used. The three species included in the analysis employed their four forward arms for exploratory behaviors about 60% of the time, while rear arms were used more frequently for stilting and rolling actions that assist forward motion, the study published Thursday in Scientific Reports found.

"All of the arms can do all of this stuff — that’s really amazing," said co-author Roger Hanlon, a marine biologist at the Marine Biological Laboratory in Woods Hole, Massachusetts. Hanlon and colleagues manually scored limb positions and actions from clips recorded between 2007 and 2015 in the Atlantic Ocean and Caribbean Sea. The dataset is the first large-scale effort to quantify precise limb actions in wild octopuses, the authors said.

Previous laboratory studies have sometimes suggested lateral preferences in octopus limb use, but the new work found no consistent right- or left-arm dominance in natural settings. "The forward arms do most of the exploring, the rear arms are mostly for walking," said Mike Vecchione, a zoologist at the Smithsonian National Museum of Natural History who was not involved in the research.

Octopus arms are multifunctional, the study notes. Each limb bears between 100 and 200 suckers that act as complex sensory organs, providing touch and chemical information that scientists compare to human senses such as smell and taste. That sensory capacity helps explain why arms are often extended to probe the environment. If an arm is lost to a predator, octopuses can retract and regrow it, providing redundancy in a body plan with eight largely capable appendages.

Janet Voight, an octopus biologist at the Field Museum in Chicago who did not participate in the study, praised the researchers’ effort. "I’m in awe that the researchers managed to do this," she said, noting the difficulty of gathering clear behavioral footage of largely reclusive animals that spend much of their time hidden in dens.

The researchers said that distinguishing limb roles in wild behavior complements laboratory experiments and advances understanding of how octopuses coordinate multiple flexible appendages. By documenting consistent positional differences in function — forward arms for exploration and rear arms for propulsion — the study provides a baseline for future inquiries into octopus motor control, sensory processing and ecology.

Data for the study were drawn from opportunistic recordings gathered over several years rather than a controlled experimental setup, a factor the authors acknowledged when describing limits on interpreting causation. Still, the analysis offers the most detailed picture to date of how wild octopuses deploy their arms across everyday behaviors.