An octopus is one of the most miraculous creatures in the ocean, and to many people, its eight legs are the feature that first comes to mind.
Having eight sucker-covered legs gives the octopus huge advantages in movement and hunting. Still, they can be damaged when octopus predators such as larger fish, seabirds, cetaceans, or sharks strike.
Luckily, the answer to the question “Do Octopus Arms Grow Back?” is yes. Through an incredible process, the octopus can regrow lost arms.
We’re going to look at exactly how octopuses grow back arms. We’ll see that the octopus can grow an entirely new arm if necessary that’s just as good as the one it replaced.
Can Octopus Grow Back Limbs?
In studying these fascinating creatures, scientists have known for a long time that the question “Can octopus grow back arms?” is answered with a firm yes. However, they’re only just fully understanding how the process works, and we will find out about that below.
Have you seen the fantastic Netflix movie My Octopus Teacher? If not, you really should!
If you have seen this award-winning film, you might remember that the octopus lost a leg during an attack by a pajama shark but that she could slowly regrow it afterward.
Unlike the starfish, where in some species, the severed leg grows a new “body,” the cut-off octopus arm will eventually die (more on that later).
When it loses a tentacle, the octopus will grow a completely new one, fully equipped with suckers, in a process called morphallaxis.
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As soon as the tentacle is damaged or lost entirely, the octopus begins to repair or regrow the limb.
In most cases, it takes between about 100 and 150 days for the octopus to grow its new, fully-functioning tentacle.
Incredibly, this new limb will be just as good as the original once the process is finished.
An octopus arm is a highly complicated organ. The octopus uses the eight flexible, prehensile appendages in every aspect of its life, including movement, feeding, and reproduction.
So complex are the arms that they contain two-thirds of the octopus’s neurons, meaning that they can make complicated reflex actions without the brain’s input. In fact, it’s often said that each arm has its own mini-brain.
Accordingly, and amazingly this means that to regrow a new arm, the octopus isn’t just growing new blood vessels, muscles, skin cells, and suckers, but also a completely new, highly complicated, mini-brain nervous network.
With their astonishing ability to regrow severed octopus arms, the over 300 species that make up the order Octopoda are genuinely some of nature’s most incredible creatures.
How Does an Octopus Lose Its Tentacles?
So, we’ve agreed that “can octopus grow back limbs” is true. But what might cause an octopus to lose one or more of its valuable arms?
Octopuses can lose their tentacles during an attack by a predator, when hunting, during reproduction, and during everyday life. It’s even possible that the octopus can lose a limb deliberately.
Scientists studying octopuses have found that limb loss or damage is prevalent, so it’s fortunate that octopuses can grow their arms back.
A common octopus (Octopus vulgaris) survey in the Bay of Naples found that over 50% had damage to at least one arm.
Another study found that the Pacific pygmy octopuses caught (Paroctopus digueti) exhibited a rate of at least 26% arm damage.
Deliberately
Amazingly octopuses can perform what is called arm autotomy, where they can detach their own tentacle. This is similar to how lizards like the skink can deliberately sever their tail when they need to.
An octopus might choose to do this if the arm has got trapped or damaged. They may also deliberately lose an arm if under attack from a predator in what is thought to be an effort to create a distraction through which they can escape.
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Predation or Feeding
More obviously, perhaps, leg injuries can occur when a predator is attacking the octopus. They can also happen when the octopus is hunting, and the meal fights back.
Octopuses enjoy eating crustaceans like crabs which will use their claws to try and save themselves. This can often lead to damage or detachment of a leg or two.
Reproduction
During octopus sex, the male octopus may lose his specialized leg called a hectocotylus, which transfers sperm to the female.
This so-called “detachable penis” can be lost deliberately when the male removes it during reproduction either as part of the process or to escape the aggressive female who may attempt to eat their partner during copulation.
Pregnant female octopuses can lose more than 50% of their body weight after laying their eggs as they tend them for weeks without feeding. The octopus can metabolize their tissues to survive via autophagy, which can often cause limb loss.
Unlike the other causes of lost limbs, lost arms in reproduction or afterward will not grow back.
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Most octopuses enter senescence, where their cells stop reproducing and repairing themselves after mating. For male octopuses, this starts immediately, and they will die after a few weeks or months.
The female octopus will aerate and protect the eggs until they hatch, after which they will also die.
The only exception is the larger Pacific striped octopus (LPSO), which can reproduce several times during its two-year lifespan. During this period, before the final senescence begins, it can continue to regrow lost arms as normal.
Can Severed Octopus Arms Still Function?
Incredibly severed octopus arms can function for a while after being disconnected from their owner.
Remember that each octopus leg has a significant neural capacity. This allows the severed octopus arm to continue to carry out some of its automatic responses.
In a 2013 study, scientists proved that severed octopus legs could react to “noxious stimulus without reference to the brain.”
The scientists applied pinch forces, freshwater, or acetic acid to the chopped-off arms, and all made a flinching reaction. Saltwater and gentle touches didn’t receive the same nervous system response proving that the severed tentacles were autonomously responding to the discomfort they felt.
It’s believed that nociceptors in the leg dedicated to sensing physical danger feel pain and use the “mini-brain” to trigger an appropriate defense response that would otherwise need the octopus brain.
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Other researchers have found that severed tentacles can crawl on their own and that if they encounter food, they would grasp it and automatically try to pass it to where the octopus mouth should be.
However, without receiving oxygenated blood and nutrition, this independent movement can’t go on forever, and typically after one hour, the octopus arm nervous system succumbs and dies.
Can Octopus Survive Losing an Arm? 2? 3?
Yes, an octopus can survive losing an arm, and as we’ve already discovered, whatever the cause was, the octopus can grow its arm back reasonably quickly.
The octopus arm regeneration process starts as soon as the arm is lost or damaged. The skin surrounding the wound tightens to close the area for the regeneration to begin.
In the meantime, if the octopus has lost just one leg, then it’s got seven more to be using. In research, damage to one or two legs simultaneously appears to be pretty standard.
Under normal circumstances, most octopuses will use their back two legs predominantly for walking on the seabed, keeping the remaining three pairs for grasping objects and eating.
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However, octopuses are highly adaptable and can manage the loss or damage to several legs at a time without suffering.
It’s generally considered that an octopus could lose a maximum of half its legs at one time before it would start to have difficulties. Fortunately for the research octopuses, little testing has been done to see just how few legs an octopus can survive with!
How Does an Octopus Regenerate Its Arms/Tentacles?
The most critical question surrounding can octopus regenerate limbs is surely HOW does an octopus regenerate arms?
A 2013 paper in the Journal of Experimental Marine Biology and Ecology by experts in molecular medical work added a new understanding of how the octopus can regenerate whole-body structures involving the protein acetylcholinesterase or AChE.
There is hope that scientists and doctors could eventually develop this information to produce significant advancements in regenerative medicine so that human limb regeneration may be possible one day.
Wound Healing, Regeneration, and Renewal
To try and understand the arm regeneration process, let’s take a step-by-step look at what the experimental marine biology scientists observed when studying how an octopus regrows damaged arms.
The scientists anesthetized six completely healthy female common octopuses (Octopus vulgaris) and removed a one to two-centimeter piece from the tip of each leg.
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The octopuses all recovered from the anesthetic and appeared unaffected by the surgery as the arm tip grew back.
First Hours
Within just hours of the surgery, the tissue surrounding the wound tightened to reduce the wound size.
Hemocyte immune system cells flooded the site and cleaned the wound by removing dying tissues to clean the wound.
Day Three – Stem Cells
No later than three days after the wound, instead of forming a scab, biochemical signals flowed into the arm to cause a knob to develop over the site, which was covered in a thin layer of epithelium cells.
The protective knob blocks pathogens in the water without interfering with the regeneration.
Underneath this hook-like structure, undifferentiated cells called a blastema started to accumulate to replace the lost tissue. These stem cells can develop into all of the different cells and systems needed inside the arm, including skeletal structure, nerve bundles, muscle cells, and even suckers.
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Day 11 to 17 – Blood Vessels
The undifferentiated cells continued to accumulate and divide to make more and more cells, and the hook-like structure above them became more pronounced.
Large numbers of blood vessels pour in to supply the regeneration site, and the stem cells beneath the hook-like shape began to differentiate into all the different parts of the arm visibly.
By Day 28
The temporary blood vessels and undifferentiated cells, along with the hook-like structure, disappeared, leaving the required specialized cells to grow into the new arm tip.
By Day 55
All the missing parts of the arm had appeared and now just need to grow and strengthen as the regenerative process finalized.
After 130 Days – Regenerative Process Complete
The octopus arm was complete again, with the restored tip completely recovered and functioning as good as the original lost tissue.
The Protein Acetylcholinesterase or AChE
Acetylcholinesterase is an enzyme found in the nervous system of many animals. It exists in humans, where it’s mainly measured in brain synapses and neuromuscular junctions.
AChE protein is used to send nerve signals across gaps or stop them dead, but it’s been discovered that it also plays an essential part in stem cell differentiation. When the scientists investigated the octopus’s limb recovery, unexpectedly high levels of AChE were found during certain parts of the process.
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When the scientists checked AChE levels in the undamaged areas of the octopus, it was only found in the nerve cord as expected.
However, during the third week after the injury, as suckers and new skin cells began to appear, AChE flooded the regenerating arm.
After 42 days, the levels decreased until they were back to normal when the severed limb had completely regenerated.
Although discovering the AChE protein didn’t wholly answer just how the undifferentiated stem cells transform into completely new octopus tentacles, it provided valuable new information, particularly for the doctors leading the way in regenerative medicine.
How Long Does It Take an Octopus Arm to Regrow?
Now we know how do octopus grow back tentacles, it’s interesting to consider how long it will take after the octopus loses the tissue.
Depending on the severity of the loss, the octopus needs about 100 to 150 days to grow its new arm. Partially cut-off limbs will naturally be quicker to heal than a fully severed arm.
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While the arm regeneration process is taking place, the octopus will tend to stay in its den more than usual to allow the arm to grow back undisturbed as much as possible.
Is the New Grown Tentacle as Good as the Old One?
The impressive regenerative process allows the octopus to grow a fully functional arm that is as good as the old one.
When a skink regrows its tail, the new one is often stubby and not as impressive as the original. However, the octopus arm regeneration process results in a perfectly functioning replacement.
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Why Can Octopus Regrow Their Limbs?
Having eight legs gives octopuses tremendous advantages when it comes to movement and hunting. However, an octopus lives a pretty dangerous life, and losing a limb is an everyday hazard.
As the octopus roams the rocky ocean floor or coral reef, it’s easy to get a leg caught as it searches a hole for food, and of course, the food might fight back.
Losing one or more arms would put the octopus at risk of not being able to feed properly or defend itself when a predator attacks.
Being able to regrow a completely functioning limb entirely means that, after a period of time, the octopus can continue its life as normal. That’s quite a feat, even if it does take a few months.
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Conclusion
We’ve confirmed that the answer to “Do octopus arms grow back?” is most definitely, and astonishingly, yes!
Octopuses have evolved the incredible ability to regrow parts of damaged arms or even grow an entirely new, fully functioning arm if needed.
An octopus might lose an arm during reproduction, feeding, or when protecting itself from a predator. They can even deliberately cut a tentacle off if it gets trapped!
Octopus arms are astonishing in themselves, and thanks to their complicated nerve cord that’s like a mini-brain, they can still function and move for a while if they get cut off.
When an octopus does lose an arm, it can survive while the regrowth process kicks in. This takes up to 150 days, depending on how much of the arm needs to regrow.
Scientists are incredibly interested to discover precisely how octopus arm regeneration works. It’s known that stem cells and blood vessels gather at the wound site to rebuild the severed arm.
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It’s hoped that once the complete secrets of the octopus’s regenerative abilities are uncovered, they may be able to help doctors studying molecular medical work develop techniques to enable human limb regrowth.
So, can octopus arms help injured people as well as themselves? Only time will tell!
British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.