All Arms on Deck 

Octopi may have eight arms, but this does not mean they use them interchangeably.  

In a new study on how octopi use their arms, researchers said the creatures – like primates, rodents, and fish – have specific arms for specific tasks. 

They came to this conclusion after analyzing 25 one-minute video clips of 25 wild octopi spanning three species engaging in different activities. The clips were filmed between 2007 and 2015 at six different sites in the Atlantic, the Caribbean, and Spain, all representing different habitats. The team gathered almost 4,000 separate arm actions, Smithsonian Magazine explained. 

For each clip, scientists and researchers classified the behavior of the octopi, such as fetching an object or walking. Then, they classified the arm actions involved, such as curling the limb or reaching it away from the body, the Guardian wrote. 

They came up with four basic ways an octopus’ arms can perform – shortening, elongating, bending, and twisting – and observed which of those ways was involved in each specific action. They also identified 12 arm actions, such as grasping, curling, tucking, and reaching. 

By combining the actions and arm movements, researchers found that octopi could perform 15 different behaviors, including exploring rocks, searching the ground, walking, swimming, and descending upon an object in a “parachute attack,” with arms outstretched and webbing extended. 

Some movements, like crawling or a parachute attack, required more arm actions than others, like backward swimming. 

The results showed that multiple arm actions could take place simultaneously on the same or adjacent arms. Moreover, all eight arms could perform all actions and movements. 

“This means that octopuses can be very flexible and adaptable in many different environments and tasks,” said Buresch. 

The animals did not show favoritism between right and left arms, but they did demonstrate a preference for using their front arms overall. 

“In general, we did see that for most actions the octopuses used their front arms more often than their back arms,” study author Kendra Buresch told the Guardian. However, there were exceptions. 

For example, they used rear arms for locomotion, to sit upright or roll along the ocean floor. Meanwhile, front arms were more often used for exploring. 

These findings could help advance the work of ethologists, sensory ecologists, neuroscientists, and engineers working on soft robotic appendages, the team wrote. The research was partially funded by the US Office of Naval Research, which wants to develop more flexible robotic arms. Those robots could help deliver necessities to people in emergencies. 

“How do you deliver a drug or a phone or water to someone who’s down there (in a collapsed building),” study author Roger Hanlon said in a statement. “You need some snaky little arm with high flexibility that can not only get down there, but can do something useful when it arrives.”