Octopuses can use their flexible arms to walk, hold and manipulate things, and reach into crevices. Now, researchers have delved into the complexity of an octopus’ limbs and say their findings might help improve the development of soft, flexible robotic arms that could even save lives.
Made up of four muscle groups around a central nerve, octopus arms are a marvel – but they’re not very well understood by scientists. We know that octopuses use their arms for lots of different things – including moving around, hunting, eating, and fighting – but exactly how they coordinate their many limbs is still unclear.
“Octopuses are unique in that they have eight flexible appendages that can bend, shorten, elongate and twist (arm deformations) in all directions due to the octopus’s extensive nervous system in each arm and the complex arrangement of their arm musculature (and lack of bones),” says Dr. Chelsea Bennice, a marine biologist at Florida Atlantic University Marine Science Laboratory. “No other animals are capable of such extreme arm flexibility and control.”
In a new study published in the journal Nature Scientific Reports, researchers analysed 25 videos of octopuses in their natural habitat to see which arms they used for 15 different behaviours and what combination of arm movements they used.
Their findings show that these animals can use all their arms to execute the tasks but do have a preference – and it wasn’t left versus right handedness. “They use their front arms more frequently than their back arms for most arm behaviours,” says Kendra Buresch, a biologist at Marine Biological Laboratory. The front four arms were used 64 percent of the time compared to 36 percent for the back arms.
The scientists noticed that the octopuses were more likely to use their front four arms for exploration while actions that help them move along were more likely to be performed by their rear arms. “In nature they selectively divide up the way that they use their front and back arms,” says Bennice.
They use “the front arms more often for most arm behaviours (such as reaching and tucking and curling their arms) with the exception of two arm behaviours that support locomotion – stilt and roll – which are used more often in the back arms.”
Both stilt and roll look the way they sound. When an octopus performs the ‘stilt’ action, it stretches its arm downwards to lift itself up, as if on stilts. ‘Roll’ is a conveyor-belt-like motion in which the octopus’ arm rolls underneath its body to help it move along.
Other actions identified included: reach, raise, lower, tuck, curl, push, parachute, grasp and tiptoe.
Studying the videos in minute detail also revealed that some actions happen more in one part of the octopus’ arm than another.
If humans can learn the secrets behind the agility of octopuses’ arms, it could help us build robots that could rescue people from collapsed buildings or deliver food and water through tiny spaces. For example, if a building collapses, “how do you deliver a drug or a phone or water to someone who’s [trapped] down there?” says Dr. Roger Hanlon, ethologist and marine biologist at the Marine Biological Laboratory, Woods Hole. “You need some snaky little arm with high flexibility that cannot only get down there but can do something useful when it arrives.”
Top image: Octopus arm raise (Octopus americanus). Credit: Credit Chelsea Bennice
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