Why do Octopus have 3 Hearts, 9 Brains, and Blue Blood? Smart Suckers!

Octopus by Jeahn Laffitte on Unsplash

Learning about fascinating creatures is a passion of mine, and one of the most amazing creatures I’ve run across is the octopus.  The description in the title above says it all – these animals are REALLY INTERESTING!!  Be prepared to have your mind stretched in eight different directions!

Octopuses have 3 hearts, because two pump blood to the gills and a larger heart circulates blood to the rest of the body.  Octopuses have 9 brains because, in addition to the central brain, each of 8 arms has a mini-brain that allows it to act independently.  Octopuses have blue blood because they have adapted to cold, low oxygen water by using hemocyanin, a copper rich protein.

When You Have 9 Brains – What are 8 of Them Doing?

We know that octopuses are intelligent, because they like to play and use tools – but we have no way of relating to what it would be like to have 9 brains.  The central brain is a doughnut shape that forms a ring around the esophagus, so when an octopus swallows, its food must ‘pass through’ the brain!  What a concept!  Food for thought…?

The most interesting thing is that they have a mini brain in each arm.  This adds up to a lot of distributed brain power.  Since each arm has a mini brain, the central brain just sends a higher-level signal to the arm; something like “move to crevice for possible crab.”  In our case, our brain would guide and control each movement of our arm.  With an octopus, the arm acts almost independently as it proceeds to probe into the crevice, tasting and feeling with its suckers. 

Octopus Bonaire
Octopus, Bonaire. Photo by Vlad Tchompalov on Unsplash

Multiply this eight times for eight arms and we can see that the mini brains take a big load off the central brain. Each arm is controlled by an elaborate nervous system consisting of more than 40 million neurons connected to the octopus’s suckers.

Researchers have found that 180 million neurons in the central brain are connected to more than 40 million neurons in each of the eight arms.

Perhaps the central brain feels like the conductor of a symphony!

We know octopuses are brainy – but how smart are they? Read my in-depth article to find out! (Hint: your average dog has only one brain!)

Fun Fact! If an octopus loses an arm, it can regenerate a perfectly functioning replacement – complete with a new mini-brain – in 100 days! Read how – click here!

For something different check out my article on the Koala’s brain – a mammal that has lost brainpower through natural selection – Why it Can Pay to be Dumb!

Keep an Eye on Your Arms to Find Some Food

One strange thing is that an octopus doesn’t know where its arm is unless it can see it. 

The arm is sending signals about taste and texture but no details about location and orientation.   In our bodies we have an ability called proprioception that lets us know where our arms are even if they are out of sight.  We can scratch our backs with precision because we know where our hand is relative to our back.

Octopus suckers can taste
Octopus keeping an eye on its suckers. Photo by Jeahn Laffitte on Unsplash

Octopuses haven’t ‘missed-out’ on acquiring this useful ability.  They don’t know exactly where their arms are for a good reason!  We carry a fixed “map” of our body in our brain, but that would be impossible for an octopus, since their body shape is so fluid and constantly changing. 

Another interesting question about having eight arms covered with suckers – how do they keep all those arms from sticking to each other and getting all tied up in knots? Especially when they don’t know exactly where their arms are.  Turns out that octopus skin secretes a chemical to keep the suckers from sticking to it.  Sounds essential for avoiding a tangled mess!

Octopus Sex and the Thrill of Surviving

Talking about arms let’s touch on sex!  Yes, there is one arm that plays an important role in octopus sex.  It is called the hectocotylus (try to spell that with your eyes closed!). 

The hectocotylus is a specially adapted arm that the male octopus uses to pass his sperm to a receptive female.  Octopus sex deserves an entire article of its own (which I have written! see How do Octopuses Mate? Cannibalistic Sex! How does a Detachable Penis Work?) Check it out!

Screenshot of Biogeoplanet.com Octopus article header
Interested in Amazing Sex? Octopus Sex? Read my article!!

In this article I get into the nitty gritty… did you know that a male octopus can have an erection? Sounds like a good conversation starter, doesn’t it?!!

The gist is that when a male and female octopus mate, the male reaches over with his specialized arm and delicately deposits one or two packets of sperm underneath the female’s mantle.  And then he backs off quickly.  He needs a long arm for this special delivery because the female can become cannibalistic as soon as she receives his love-packet.  Now that she has his sperm the male is only good for one thing – nourishment!!

Octopus mating
Octopuses mating, showing male’s hectocotylus. Photo copyright Tim Nicholson.

Cannibalism makes good sense from the female’s perspective, since she will need to be well-nourished to produce thousands of eggs and to spend months looking after them without feeding.  Each female lays up to 100,000 fertilized eggs in clusters under an overhang. In most species the females constantly guard, clean and oxygenate the eggs for up to seven months before the young hatch.  The mothers never feed during this period and can lose more than 50 percent of their body weight before the young hatch.  In most species the females die shortly afterwards.

Sex is bad for the health of the males, as well.  Once they’ve mated the males begin to decline rapidly as they enter a period of senescence.  They stop eating and begin acting erratically, until they die shortly afterwards.

Why Would You Need 3 Hearts?

An octopus might ask, how can humans manage with just one heart? 

Many of the octopus species live deep in the oceans where there is less oxygen available and the water is frigid.  Given this environment, octopuses have evolved three hearts to help get sufficient oxygenated blood to all parts of the body, even to the tips of the arms.  Two hearts pump blood to the gills and a larger heart takes the oxygenated blood and circulates it to the organs and the rest of the body. 

In some species, the larger heart stops beating when the animal swims. I guess it better not swim for too long!

True Blue Bloods have a Thing for Copper

Since many octopus live in cold deep waters, they’ve adapted by using a copper-rich protein called hemocyanin to oxygenate their blood rather than our iron-rich hemoglobin.  This gives a blue tint to their blood, while hemoglobin turns our blood red. 

Because their copper-based blood is not an efficient oxygen carrier, octopuses favor cooler oxygen-rich water.

Watch the Octopus Disappear!  Camouflage Colors and Textures

One of the most amazing demonstrations of octopus camouflage that I’ve seen was filmed by Professor Roger Hanlon, University of Chicago.  It shows a seaweed covered boulder turn into an octopus – like magic!  And then he reverses the video and you can see the octopus become one with the seaweed and the boulder.  Look at the video below to see for yourself.

Not only does the animal acquire the colors of the background seaweed and boulder but it changes the texture of its skin to match.  There are millions of pigment cells or chromatophores in the skin and millions more of the nerve endings needed to create the skin texture.

Octopuses are Not Here for a Long Time – Hope it’s a Good Time!

It is surprising that octopuses have so many amazing abilities going for them and yet their lifespan is short – only three to five years. 

If they lived for as many years as we humans do, they would probably be running the planet by now!  Because of their life-cycle they lack one of the characteristics that we consider important for an advanced species.  Octopuses don’t care for their young, so there is no inter-generational learning.

This means that each individual octopus must discover and learn everything that it needs to know to survive on its own. 

Imagine that!  No parents around to tell the youngsters how to behave.  For some human teens this might seem like a dream come true!  But for a species as a whole, it results in major limitations.  Not being able to pass on the wisdom gained by previous generations means a whole lot of learning gets repeated and rediscovered by each succeeding generation. 

Congratulations! You must be pretty keen on octopuses to read this far! Are you certain you only have one brain?!

Another Amazing Octopus Ability – Regenerating Lost Appendages!

The octopus is one of the few creatures that can regrow a completely severed or damaged appendage so that it is as GOOD as new and indistinguishable from the original. A missing arm can be completely regenerated in roughly 100 days.

In the case of the octopus, this means regenerating an entire mini brain from scratch! To find out more about this amazing ability take a look at my article on Octopus Regeneration.

Image of post explaining how octopuses regenerate lost arms

Fun Facts and Not-so-Fun Facts

  • Octopuses grow quickly, gaining up to 2 percent of their body weight a day.  This is based on a remarkable 50% efficiency in converting food energy into mechanical output.  Humans are only half as efficient at 25%.  (Thank goodness I say!  Imagine 50% of every doughnut going straight to your waist!)
  • Octopuses have over 2,000 suckers.  Each sucker operates independently and features chemo-receptors that can taste everything they touch.  (Which can be kind of icky if you think about it!)
  • They kill their prey by thrusting their sharp tongue, much like a small rasp or file, into the victim and injecting venomous saliva.
  • After hatching, octopuses live as tiny paralarvae drifting around in clouds of plankton near the ocean surface.  
Octopus larva in Zooplankton
Octopus paralarva in plankton layer. Photo by NOAA
  • Octopus paralarvae feed on the abundant zooplankton — but life in the plankton layer is perilous – they take a turn at becoming food for the billions of other creatures that feed on plankton.
  • Biologists estimate that out of 50,000 to 75,000 eggs laid, only 2 will survive to become mature adults.
  • Octopuses are highly intelligent, somewhat comparable to your pet cat or dog.  Their abilities in navigating mazes and their problem-solving skills show that they have both short and long-term memory.

Don’t forget to check out my article on fascinating facts about octopus sex – including a detachable penis! (Can male octopuses have an erection? Find out!)

Can an Octopus Kill You? One Word – Sannakji

Imagine trying to eat a live octopus, with the arms still squirming on the plate.

The Korean dish Sannakji features live baby octopus arms cut into pieces and served fresh and mobile.
Those of us who know that each arm has a mini-brain of its own might think twice about trying to swallow a live octopus arm. Even when an arm is severed from its body, the suckers will keep applying suction. This means that arms must be well chewed before swallowing, otherwise they will stick to the mouth and throat.

Sannakji is a Korean dish consisting of live octopus arms. Photo by Rusif Huseynov, CC BY-SA 3.0, via Wikimedia Commons

Apparently, an average of six people choke and die from wrapping their mouths around sannakji each year.

Yes, a live octopus can kill you, especially if you are dumb enough to stick one into your mouth.

Want to know more about octopuses? 

Check out my series of articles on these fascinating creatures:

How do Octopus Reproduce? (Cannibalistic Sex and a Detachable Penis)

How Smart are Octopuses? (Are Octopuses As Intelligent as Dogs?)

Why do Male Octopuses Die after Mating? (How does Octopus Senescence work?)

Can Octopus Arms Grow Back? (Are Regenerated Limbs Just as Good?)

Check out these Octopus Gifts for the Octopus Lover in your Life

Octopus fans love to wrap their arms around Octopus gifts and Octopus books. It doesn’t take 9 brains to realize that octopuses are some of the coolest creatures on the planet!

Watch my Octopus Presentation

I have given hundreds of presentations to large audiences interested in marine creatures. Of course, octopuses stand out as one of my favorite topics… watch my presentation to see why.


Monterey bay aquarium provides an excellent series of octopus videos that I can highly recommend.

CephBase: The comprehensive website at CephBase is an authoritative source of data and factual information for the CLASS CEPHALOPODA – squids, octopuses, cuttlefish and nautilus. 


Zullo, L., Eichenstein, H., Maiole, F. et al. Motor control pathways in the nervous system of Octopus vulgaris arm. J Comp Physiol A 205, 271–279 (2019). https://doi.org/10.1007/s00359-019-01332-6

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George Sranko

George Sranko, B.Sc., MA (Hons), is a retired professional biologist, photographer, author and speaker. He has explored fascinating nature topics and epic destinations for over 40 years, beginning with his first job as a National Park naturalist. George is a popular destination and science lecturer on cruise ships throughout the world, with hundreds of presentations under his belt. He has visited over 90 countries and happily shares his personal experiences and insights in a dynamic and entertaining style.

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