World Octopus Day

Celebrating Nature’s Eight-Armed Genius

Every October 8, World Octopus Day celebrates one of the strangest, smartest and most accomplished escape artists in the ocean. The octopus can solve problems, manipulate objects, change its appearance in seconds, squeeze through astonishingly small openings and disappear behind a cloud of ink when circumstances become socially inconvenient. It has three hearts, blue blood, eight extraordinarily capable arms and enough peculiar biology to make most other animals look as though evolution simply wasn't trying very hard that afternoon.

World Octopus Day is part of the wider Cephalopod Awareness Days, an informal celebration of octopuses and their remarkable relatives, including squid, cuttlefish and nautiluses. October 8 is particularly appropriate for the octopus because, conveniently enough, it has eight arms. There are hundreds of known octopus species living throughout the world's oceans, from shallow tropical reefs and rocky coastal waters to the cold, dark depths of the deep sea. They vary enormously in size and appearance, but collectively they represent one of the most remarkable branches of animal life on Earth.

Octopus Intelligence: There’s Quite a Lot Going On in There

Calling an octopus intelligent isn't simply something aquarium employees say because the octopus keeps stealing equipment. Scientists have documented sophisticated learning, memory, exploration and problem-solving behavior among octopuses. They can navigate mazes, open containers and learn how to manipulate unfamiliar objects. Some species have even been observed carrying coconut shells and assembling them later as shelters, behavior frequently discussed as an example of tool use in an invertebrate.

What makes octopus intelligence particularly fascinating is the way its nervous system is organized. A large proportion of an octopus's neurons are located outside its central brain, especially throughout its eight arms. The arms can process sensory information and perform complicated movements with a surprising degree of independence while remaining coordinated with the central nervous system. An octopus therefore experiences and interacts with its surroundings in a manner profoundly different from humans and other vertebrates.

Those arms are impressive pieces of equipment in their own right. Depending upon the species, an octopus can possess hundreds of suckers, allowing it to grasp, investigate and manipulate its environment with extraordinary precision. The suckers contain sensory receptors that provide information about both touch and chemicals in the environment, effectively allowing an octopus to gather information about something simply by grabbing hold of it. Humans generally have to read the label. The octopus just sticks several suckers on the problem and gets on with it.

Eight Arms, Not Eight Tentacles

Here’s a useful bit of octopus trivia for World Octopus Day: despite what many of us have been saying since childhood, an octopus doesn’t actually have eight tentacles. It has eight arms. It may sound like scientists are being unnecessarily fussy, but there really is a difference.

An arm has suckers running along much of its length, while a tentacle is usually longer and has most of its suckers concentrated near the end. Squid and cuttlefish, for example, have eight arms as well as two longer tentacles that help them grab prey. The octopus manages perfectly well without the extra equipment, using its eight flexible arms for walking, swimming, exploring, hunting, handling food and investigating anything that happens to catch its attention.

Those arms are remarkably sensitive. Depending on the species, an octopus may have hundreds or even thousands of suckers spread across them. The suckers don't simply provide a powerful grip; they also allow the octopus to touch and chemically examine its surroundings. In effect, an octopus can learn something about an object simply by grabbing hold of it, which probably explains why keeping one in an aquarium can occasionally become an interesting battle over who actually owns the equipment.

The name itself provides a clue to all this. “Octopus” comes from Greek words meaning “eight” and “foot.” Fortunately, scientists settled on calling them arms rather than feet, otherwise World Octopus Day would inevitably involve a lengthy discussion about shoes.

Eight of them.

Masters of Octopus Camouflage

An octopus doesn't need a wardrobe because it essentially wears the scenery. One moment it can be sitting in plain sight, and seconds later you may find yourself staring directly at it while wondering where on earth it went. This extraordinary ability to change appearance is one of the octopus's most effective defenses against predators, but camouflage is only part of the performance.

An octopus can change its color, pattern and even the apparent texture of its skin with remarkable speed. Special pigment-filled cells called chromatophores allow different colors and patterns to appear across the body, while other structures in the skin reflect light. At the same time, muscles can raise or flatten tiny areas of skin, allowing a smooth-looking octopus to suddenly become rough and bumpy. Against rocks, coral or a complicated seabed, the result can be astonishingly convincing.

Surprise an octopus and things can become even more interesting. A startled animal may suddenly become much darker or paler, produce bold patterns across its body, alter the texture of its skin and change its posture. Its arms may draw inward or spread outward, and the entire animal can seem to transform before your eyes. These rapid changes aren't necessarily an attempt to imitate one particular object. Depending on the circumstances, they may help the octopus hide, confuse a predator, appear more threatening or simply react to whatever has just disturbed it.

Color changes can also reveal something about what an octopus is doing. Researchers have observed different patterns during hunting, resting, encounters with other octopuses and defensive behavior. We shouldn't assume that every shade represents an octopus version of a human emotion—there isn't a simple dictionary translating dark brown into “Who sneaked up behind me?”—but its constantly changing appearance clearly plays an important part in how it responds to the world around it.

Some octopuses take disguise to extraordinary levels. Rather than simply matching the background, they can alter the way they hold and move their bodies to make themselves less obvious. The famous mimic octopus goes considerably further, adopting shapes and movements resembling other sea creatures. Apparently disappearing wasn't impressive enough; somebody had to add impersonations.

When Camouflage Fails, Release the Ink

Even the finest camouflage has its limits. If a predator spots an octopus and decides that eight arms look particularly appetizing, the octopus still has another famous defensive trick available: ink. Many octopus species can suddenly release a dark cloud into the surrounding water, creating enough confusion to give themselves a valuable few seconds to escape.

The ink is produced in a special sac and released into the water through the same funnel-like opening the octopus uses to propel itself. When danger arrives, the animal can eject ink and rapidly force water from its body, sending itself away from the threat at considerable speed. To the unfortunate predator, one moment there is an octopus and the next there is a dark cloud accompanied by a distinct shortage of lunch.

The ink does more than simply block the view. It contains substances that may interfere with the senses of some predators, particularly their ability to detect the octopus chemically in the water. An octopus can also release thicker blobs of ink and mucus that briefly resemble a dark shape in the water. A pursuing predator may investigate the decoy while the genuine article heads rapidly in the opposite direction. Apparently the octopus discovered the usefulness of leaving a forwarding address occupied by somebody else.

There is another reason the trick works so well. An octopus is built for a quick getaway. By drawing water into its body and then forcing it through its siphon, it can use jet propulsion to shoot through the water. Its soft body and flexible arms can then help it disappear into a narrow crack, beneath a rock or inside a hiding place where many larger predators simply cannot follow.

Ink isn't something an octopus wastes casually. Producing it requires resources, and releasing ink in a confined space can even create problems for the octopus itself if the water isn't circulating properly. Camouflage and hiding are therefore excellent first choices. But when subtlety has failed and something with teeth is getting uncomfortably close, the octopus has an admirable emergency procedure: make a mess, confuse everybody and leave.

Three Hearts and Blue Blood

As if eight arms, disappearing acts and an emergency ink supply weren't enough, the inside of an octopus is every bit as unusual as the outside. An octopus has three hearts. Two of them pump blood through the gills, where it picks up oxygen, while the third sends that oxygen-rich blood around the rest of the body. Three hearts might sound excessive, but when you have eight arms to supply and spend your life underwater, apparently one simply won't do.

There is another surprise flowing through those hearts: octopus blood is blue. Human blood carries oxygen using hemoglobin, which contains iron and gives our blood its familiar red color. Octopuses instead rely on a copper-containing protein called hemocyanin. When the copper binds with oxygen, it produces the distinctive blue color. Hemocyanin works particularly well in the cold, low-oxygen conditions encountered by many octopus species, making their unusual blood well suited to life in the sea.

Octopuses aren't alone in this arrangement. A number of other animals, including squid, lobsters and some crabs, also use hemocyanin and can have blue or bluish blood. The most famous example is the horseshoe crab, whose bright blue blood has become especially important to medical science. Despite its name, however, the horseshoe crab isn't actually a true crab; it is more closely related to spiders and scorpions. Nature apparently decided that three hearts and blue blood weren't quite confusing enough without throwing that into the conversation.

The three-heart arrangement has another peculiar feature. When an octopus swims using jet propulsion, the heart responsible for circulating blood around the body temporarily stops beating. Swimming that way therefore takes considerable energy, which helps explain why octopuses often prefer crawling along the seafloor with their arms rather than racing everywhere under jet power.

So an octopus has three hearts pumping blue blood through a soft body controlled by an extraordinary nervous system. If somebody invented an animal with those specifications for a science-fiction movie, we'd probably complain that the writers had gone too far.

Fortunately, the octopus doesn't seem particularly concerned about our opinion.

You Thought That Tank Was Secure?

Keeping an octopus in an aquarium presents an unusual problem: the octopus is often considerably more interested in the aquarium than the aquarium is prepared for. These animals are curious, intelligent and extremely good at exploring anything that looks even remotely like an opening. A lid that seems perfectly secure to a human may simply represent an interesting puzzle to an octopus with eight arms and plenty of time.

Much of this ability comes from the octopus's extraordinary body. It has no bones, and most of its body is soft and remarkably flexible. The main limitation is its hard beak. If an opening is large enough for the beak to pass through, much of the rest of the animal may be able to squeeze through as well. A gap that appears impossibly small can therefore become an exit, entrance or invitation to investigate somewhere it was never supposed to visit.

Their arms make matters even more interesting. Equipped with powerful suckers and an impressive ability to manipulate objects, octopuses can explore lids, pipes, tubes and other aquarium equipment. They don't necessarily understand that humans have designated one particular glass box as “where the octopus lives.” To an inquisitive animal, the neighboring tank may simply be another part of the environment worth investigating—particularly if something edible happens to live there.

Aquarium keepers have accumulated plenty of stories about octopuses turning up where nobody expected them. Some have left their tanks and entered neighboring enclosures, occasionally helping themselves to the residents before returning home. Others have discovered plumbing or drainage routes. Keeping an octopus therefore requires careful attention not only to the obvious openings but also to every small gap an intelligent, flexible animal might decide deserves closer inspection.

One of the most famous examples came from the National Aquarium of New Zealand in 2016. An octopus named Inky discovered a small opening in his enclosure, made his way across the aquarium floor and reached a drainpipe that led toward the Pacific Ocean. By the time his absence was discovered, Inky was gone. There was no dramatic pursuit, no ransom note and apparently no intention of returning.

Stories like Inky's help explain why octopuses have such a reputation as escape artists. Their success isn't based upon one special trick. It comes from an extraordinary combination of intelligence, curiosity, flexible bodies, powerful suckers and an ability to investigate and manipulate their surroundings.

Put all of that together and the question facing an aquarium keeper may not be “Can the octopus get out?”

It may be “Has the octopus noticed how to get out yet?”

What Do Octopuses Eat?

Octopuses are hunters, and despite their soft and rather squishy appearance, they are very capable ones. Their usual menu includes crabs, shrimp, lobsters, clams, snails and fish, although exactly what an octopus eats depends upon its species, size and where it lives. An octopus hiding among rocks may wait for prey to wander within reach, while others actively search the seafloor, investigating cracks and crevices with their remarkably sensitive arms.

Once dinner has been located, those eight arms become extremely useful. The suckers can seize and hold struggling prey while the octopus brings it toward a hard, sharp beak located where its arms meet beneath the body. The beak resembles that of a parrot and is strong enough to bite through or break apart surprisingly tough food. Some octopuses can also drill small holes into shells to reach the animal protected inside. Being a clam probably feels considerably safer right up until the octopus arrives with tools.

Octopuses also produce venom that helps them overpower prey. For most species, that venom isn't considered dangerous to people, although a bite can certainly be painful and deserves medical attention. The major exception is the small blue-ringed octopus, found in parts of the Pacific and Indian Oceans. Its venom can be extremely dangerous to humans, which makes its beautiful blue rings something best admired without picking up their owner.

And that raises an obvious question whenever photographs of enormous octopuses appear: Do octopuses eat people?

No. Humans are not normal prey for octopuses. Even the giant Pacific octopus, the largest commonly recognized octopus species, normally feeds on animals such as crabs, shellfish and fish. A large octopus is certainly strong enough to grab a diver, and octopuses sometimes investigate people with their arms and suckers. Defensive bites and uncomfortable encounters can occur, particularly if an animal feels threatened or is handled, but there is no established pattern of octopuses hunting humans for food.

Stories of gigantic sea monsters dragging sailors beneath the waves belong much more comfortably to folklore and adventure stories than to everyday octopus behavior. An octopus generally has little reason to regard a human being as dinner. From its point of view, we are enormous, strangely shaped creatures covered in equipment and considerably more troublesome to deal with than a crab.

Octopuses themselves, however, frequently end up on somebody else's menu. Large fish, sharks, seals, dolphins, seabirds and other marine predators may eat them, depending upon where they live. That places the octopus squarely in the middle of the ocean food chain: a skilled hunter of smaller animals while remaining potential dinner for something larger.

So if you happen to meet an octopus while swimming, you don't need to worry about being mistaken for lunch. Give it some room, don't grab it, and enjoy the encounter.

The octopus is probably wondering what on Earth you are, too.

The Remarkably Short Life of an Octopus

Considering everything an octopus learns to do, it doesn't receive much time to enjoy being good at it.

Many octopus species live only one or two years, although lifespans vary considerably among species. The giant Pacific octopus can live longer, generally several years, but even that is brief compared with many other large and intelligent animals.

Reproduction usually marks the beginning of the end. Male octopuses transfer packets of sperm to females using a specialized arm called a hectocotylus. Depending upon the species, mating can be a cautious business because octopuses are generally solitary animals and encounters between adults don't always end amicably. Being eaten by your date remains one of nature's clearer indications that things haven't gone particularly well.

After laying her eggs, a female octopus may devote herself almost entirely to guarding and caring for them. She cleans the eggs and continually moves water across them to provide oxygen, often refusing food during the process. After the eggs hatch, the mother usually dies. Males also generally die sometime after reproduction.

It is an extraordinary biological strategy: grow quickly, learn rapidly, reproduce once and leave the next generation to begin again.

Where Do Octopuses Live?

Octopuses are found in oceans around the world, from warm tropical waters to cold seas and from shallow coastal areas to the dark depths of the ocean. Different species have adapted to very different surroundings, which means there isn't really one place that can be described as typical octopus country. If there is salt water, suitable food and somewhere reasonably comfortable to hide, there is a fair chance an octopus species has found a way to live there.

Many of the octopuses people are most likely to encounter live relatively close to shore. Rocky coastlines, coral reefs, tide pools, seagrass beds and sandy or muddy seafloors can all provide suitable homes. These environments offer both food and hiding places, allowing an octopus to spend much of its time tucked away before emerging to hunt.

A good hiding place is particularly important. Octopuses often make temporary homes, usually called dens, inside cracks in rocks, beneath ledges, among coral or in holes on the seafloor. Because an octopus has such a flexible body, a space that appears far too small can make a perfectly acceptable home. The entrance may sometimes be surrounded by discarded shells and other remains from previous meals, rather like leaving the takeaway containers outside the front door.

Octopuses can also be remarkably creative when suitable accommodation is in short supply. They have been found sheltering inside empty shells, bottles, jars and other objects resting on the seabed. Some species carry shells or pieces of coconut with them and use the pieces for protection when needed. Apparently humans aren't the only creatures who appreciate portable accommodation.

Not every octopus stays close to a sunny reef. Some species live hundreds or even thousands of feet beneath the surface, where sunlight is weak or completely absent, temperatures are low and the pressure is enormous. Deep-sea octopuses have evolved to survive in these demanding conditions, and new observations continue to reveal how successfully they occupy parts of the ocean that humans have barely explored.

At the other extreme, octopuses can sometimes be found in very shallow water. Tide pools and rocky coastal areas may temporarily leave an octopus in only a small amount of water as the tide changes. Some species can even move short distances across wet rocks between pools, provided their bodies and gills remain moist. It is an impressive sight, although an octopus wandering across the rocks is probably another good reason to reconsider exactly where the boundary between landlord and tenant lies.

One thing you generally won't find is an octopus living naturally in fresh water. Octopuses are marine animals and depend upon the conditions found in salt water. There are no known freshwater octopus species, despite occasional stories and legends suggesting otherwise.

From a shallow tropical reef to the cold darkness of the deep ocean, octopuses have managed to occupy an extraordinary variety of habitats. They may look delicate, but their worldwide distribution tells a different story.

Give an octopus an ocean, something to eat and a decent hole to hide in, and it will probably start inspecting the neighborhood.

Why Octopuses Matter

Beyond being spectacular animals, octopuses are important components of ocean ecosystems. As predators, they help regulate populations of crustaceans, mollusks and other marine creatures. As prey, they provide food for numerous fish, sharks, seabirds and marine mammals.

Scientists also study octopuses to understand subjects ranging from intelligence and nervous-system evolution to camouflage, robotics and flexible materials. Their unusual biology demonstrates that sophisticated behavior and problem solving did not evolve along only one pathway. Humans and octopuses last shared a common ancestor hundreds of millions of years ago, yet both evolutionary branches eventually produced animals capable of learning, remembering and solving complicated problems.

The octopus is therefore more than an interesting animal with too many arms. It offers scientists an opportunity to examine something genuinely profound: an intelligent creature whose brain, body and senses developed along an evolutionary road dramatically different from our own.

How to Celebrate World Octopus Day

Celebrating World Octopus Day on October 8 doesn't require acquiring eight sleeves.

A visit to an aquarium is an excellent opportunity to observe a living octopus, particularly if the animal decides that observing you in return might be worthwhile. Watching documentaries about cephalopods, learning about marine conservation or simply discovering more about octopus behavior and intelligence are equally appropriate ways to mark the day.

World Octopus Day is also a useful reminder of the importance of protecting marine habitats. Pollution, habitat degradation, climate change and other pressures affecting the world's oceans inevitably affect the extraordinary creatures living within them. Healthy seas support octopuses along with the countless other organisms sharing their ecosystems.

Most importantly, October 8 provides an excuse to appreciate an animal that seems almost designed to demonstrate how inventive nature can be. The octopus has three hearts, blue blood, eight independently capable arms, remarkable intelligence, extraordinary camouflage and a talent for escaping from places humans were absolutely certain were escape-proof.

Octopus FAQ

An octopus has eight arms, so it seems only fair that our Octopus FAQ should have eight questions. We briefly considered asking one question per arm, but that raises awkward questions about which arm gets to type the answers. Instead, here are eight frequently asked questions about one of the ocean's most remarkable residents.

1. When is World Octopus Day?
World Octopus Day is observed each year on October 8. The date provides an opportunity to learn more about octopuses, their intelligence, unusual bodies, behavior and importance in marine ecosystems.

2. How many hearts does an octopus have?
An octopus has three hearts. Two pump blood through the gills, while the third circulates blood around the rest of the body. Apparently eight arms create enough paperwork to require additional management.

3. Why is octopus blood blue?
Octopus blood is blue because it uses a copper-containing protein called hemocyanin to carry oxygen. Human blood uses iron-containing hemoglobin, which makes our blood red. Several other marine animals also use hemocyanin and have blue or bluish blood.

4. Does an octopus have eight arms or eight tentacles?
An octopus has eight arms, not eight tentacles. Its arms have suckers along much of their length. Squid and cuttlefish have eight arms plus two longer tentacles, which is probably where some of the confusion begins.

5. Are octopuses intelligent?
Yes. Octopuses are remarkably intelligent animals capable of learning, solving problems, remembering solutions and investigating unfamiliar objects. They have also become famous for opening containers, manipulating aquarium equipment and discovering exits their keepers were fairly certain did not exist.

6. Can an octopus really change color?
Yes. An octopus can rapidly change its color and pattern, and many can also alter the texture of their skin. These changes help with camouflage, communication and reactions to threats. A surprised octopus can sometimes appear to change its entire appearance within moments.

7. Do octopuses eat people?
No. Humans are not normal prey for octopuses. Their diet generally includes crabs, shrimp, shellfish, fish and other marine animals. A large octopus can grab a person and an octopus may bite when threatened or handled, but people aren't on the regular menu.

8. How long do octopuses live?
Most octopus species have surprisingly short lives, often only around one or two years, although some larger species can live for several years. Their brief lifespan is one of the strangest contrasts in the octopus story: an animal capable of remarkable learning and problem-solving gets relatively little time in which to use those abilities.

Eight questions, eight answers and eight arms. For once, everything about an octopus adds up neatly.

Eight Arms and Plenty to Celebrate

World Octopus Day celebrates an animal that becomes more remarkable the more you learn about it. An octopus can change its color, pattern and skin texture, squeeze through openings that appear impossibly small, solve problems, investigate unfamiliar objects, hunt with eight extraordinarily sensitive arms and, when circumstances demand it, disappear behind a cloud of ink. Beneath all of that is an animal with three hearts, blue blood and a body designed so differently from ours that it sometimes seems as though evolution decided to try something completely new.

Perhaps the most fascinating thing about the octopus is that all these remarkable abilities belong to a real animal rather than something invented for science fiction. There are no bones inside that flexible body, its arms can perform remarkably complicated tasks, and much of its nervous system extends throughout those arms. It can alter its appearance within moments and then squeeze into a hiding place that looks far too small to contain it. Put an octopus in an aquarium and there is also a reasonable chance it will become interested in how the aquarium works—and possibly whether remaining inside it is compulsory.

Yet for all their unusual abilities, octopuses aren't simply collections of biological curiosities. They are important predators and prey within marine food chains, sharing oceans with countless other species and filling an important place in underwater ecosystems. They have survived by being adaptable, cautious, curious and exceptionally good at making themselves difficult to find when something larger comes looking for dinner.

World Octopus Day gives us an excellent excuse to appreciate an animal that many people may rarely see outside an aquarium, documentary or photograph. Learning about octopuses also reminds us how much remains to be discovered beneath the surface of the world's oceans. Even today, scientists continue studying their behavior, intelligence and remarkable bodies, while exploration of deeper waters continues to reveal species and behaviors we have barely begun to understand.

So on October 8, spare a thought for one of the strangest, smartest and most fascinating residents of the sea. It has three hearts, blue blood, no bones, eight arms and enough tricks to make almost every other animal look slightly underprepared.

And if you happen to keep one in a tank, don't just check on the octopus. Check the lid.