Author: Sam Trail
Date: September 22, 2025
In the natural world, the octopus is the “poster child” of flexibility. From performing large parachute attacks during hunting, to squeezing their arms into tiny crevices, octopus arm flexibility is an impressive feat. FAU Marine Lab Postdoctoral Research Fellow (and world-renowned “OctoGirl”), Dr. Chelsea Bennice, and her co-authors (Kendra Buresch and Roger Hanlon from the Marine Biological Laboratory at Woods Hole, Massachusetts) set out to categorize how octopuses use and coordinate their 8 arms to achieve such impressive and complex behaviors. Their findings and conclusions were reported earlier this month in the scientific journal Scientific Reports.
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Photo Credit: Chelsea Bennice |
How exactly do octopuses use their arms?
“It’s a simple question to ask but a daunting task to answer, especially when your study animal has no bones and 8 eight arms, each with almost a limitless range of movement”, said Bennice. They crawl, swim, stand, and fetch, among other complex behavioral movements! However, researchers dove in (literally) to ask what specific arms are involved in these movements, and how they performed and coordinated?
Octopus bodies are not composed of rigid elements or discrete joints like our own bony skeletons – making their potential range of motion almost unfathomably large. Instead, their body and arms possess what are called muscular hydrostats for structure and support. Two examples of muscular hydrostats are a cat’s tongue and an elephant’s trunk. In the octopus, four muscular groups form the muscular hydrostat. The way these muscles work together, either in synchrony or against one other, allow the octopus to execute four foundation arm deformations – bend, shorten, elongate, or twist. Deformations can occur anywhere along the length each arm. The objective in this study was to determine which deformations occurred during specific arm movements, where along the length of each arm they occurred, and which arms dominated in expressing those modifications. One may say- these scientists had their hands [arms] full answering these questions.
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An ethogram (or detailed animal behavior catalog) of all the behaviors, arm actions, and arm deformations described in Bennice’s arm flexibility study. |
“Our study is the first to take this uniquely hierarchical approach to understand how each arm participated in specific behavioral acts shown by octopuses in nature,” said Bennice. The authors based their conclusions on video recordings of wild octopuses under natural conditions. Their analyses classified 15 types of animal behavior, then identified and defined 12 arm behaviors that made up each of these animal behaviors. From there, they analyzed the small arm movements (deformations) that made up each of these arm behaviors. That approach led to most comprehensive ethogram of octopus behavior (essentially, a complete description of all of the acts that they perform) currently in the literature.
Bennice stated that “You have to pay close attention to how a single arm is moving for the duration of video. An octopus has 8 arms, which means we had to watch each video clip 8 times!” Since these researchers do not have eight arms to multi-task, they divided up the task of analyzing each video sample. Bennice thanks all co-authors involved, as this was a lot of work. Two additional coauthors (Jennifer Grossman and Tylar Morano) were students visiting Hanlon’s Lab to obtain research experience. They gained that experience under the supervision of Bennice and Buresch.
Bennice and her colleagues discovered that all 8 arms were capable of performing all arm behaviors expressed by the octopus, but despite this redundancy, octopuses used groups of arms for specific tasks. Under natural conditions, octopuses were more likely to use their anterior (front) arms for “exploratory” behaviors and posterior (back) arms for locomotion. Bennice and co-authors also found that three regions along the length of each arm (described as the proximal, medial, distal arm regions) are capable of all arm deformations. However, the proximal arm region (portion of the arm nearest to the octopus’s body) performs more elongations than the other arm regions, while the distal arm region (portion of the arm nearest to the arm tip) performs more bends.
Although previous lab studies indicated octopuses might have a right or left-arm preference, observations of these wild octopuses did not support that finding. “Studying and recording wild octopuses in the field gave us the opportunity to analyze a larger behavioral repertoire and further understand how these animals use their arms to achieve such complex actions,” Bennice said.
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Photo Credit: Chelsea Bennice |
Octopuses spend most of the day in their dens, often only emerging to find food or a mate. When they do emerge their impressive camouflage, including changing their skin color and texture to blend in with the environment, make them difficult to spot. Just locating octopus individuals and recording their behaviors was an arduous task that required an impressive amount of time and patience.
From 2007-2015 Hanlon and Bennice captured field video from 25 individual octopuses (all closely related species: Octopus vulgaris,
Octopus americanus, and Octopus insularis) across 6 different shallow water habitats in the Caribbean and in the coastal waters of Spain. Their analysis was a massive undertaking. In total, nearly 4,000 arm behaviors and nearly 7,000 arm deformations were recorded in this thorough analysis.
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Photo Credit: Maggie Birdwell |
A portion of this research was funded by a grant from the United States Office of Naval Research (to Roger Hanlon), which is interested in the application of octopus arm flexibility to engineering soft robotics. The unparalleled flexibility of the octopus arm serves as a model for moving through and carrying out tasks in tight and narrow spaces. Such advances could lead to life-saving technology – delivering critical materials in the catastrophic events of collapsed buildings or a sunken submersible. The study of octopus movement and flexibility could hold the key to those future designs!
This study has been making waves around the globe, now covered by more than 70 news outlets and counting! Check out additional coverage on this impressive study from The New York Times, NPR, BBC, Popular Science, Science Alert just to name a few.
Way to go, OctoGirl!
