A red octopus swimming deep in the ocean

Most of an octopus’s 500 million nerve cells are in its arms.

STUART WESTMORLAND/GETTY IMAGES

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Smart Suckers

Scientists hope to uncover the secrets of one of the ocean’s cleverest creatures

AS YOU READ, THINK ABOUT how intelligence can help a creature survive in its environment.

Several years ago, when staff at the National Aquarium of New Zealand were getting ready for the day, they noticed something fishy. Two Maori octopuses, named Inky and Blotchy, usually shared a tank. But that morning, Blotchy was all alone—Inky had mysteriously disappeared. The only clue was a wet trail leading from the tank to a nearby drainpipe. By the look of it, Inky had squirmed through a tiny opening at the top of the tank, crawled 2.4 meters (8 feet) across the floor, and wiggled down the narrow pipe that led to the ocean.

The breakout was no surprise to scientists who study octopuses. The animals are known for making bold escapes and causing mischief in captivity. Wild octopuses are no different, says Jennifer Mather. She’s a psychologist who studies animal behavior at the University of Lethbridge in Canada. Forty years ago, Mather was diving off the coast of Bermuda when she saw a common octopus do something she’d never seen before. It scuttled out of its rocky den and used one of its eight long arms to pick up a rock. It brought the rock back to the den and then left to grab more rocks. The octopus lined up the rocks to form a wall in front of the den’s opening before curling up inside. “That was my ‘aha’ moment,” remembers Mather. “Octopuses are smart!”

Several years ago, staff at the National Aquarium of New Zealand were getting ready for the day. They noticed something fishy. Two Maori octopuses, named Inky and Blotchy, usually shared a tank. But that morning, Blotchy was all alone. Inky was gone! The staff found only one clue. A wet trail led from the tank to a nearby drainpipe. It looked like Inky had squeezed through a tiny opening at the top of the tank. Then the octopus had crawled 2.4 meters (8 feet) across the floor and wiggled down the narrow pipe to the ocean. 

Scientists who study octopuses weren’t surprised. Captive octopuses are known for making bold escapes and causing mischief. Wild octopuses are no different, says Jennifer Mather. She’s a psychologist who studies animal behavior at the University of Lethbridge in Canada. Forty years ago, Mather was diving off the coast of Bermuda. Something happened that she’d never seen before. A common octopus came out of its rocky den. It picked up a rock with one of its eight long arms. It brought the rock back to the den and left to grab more rocks. The octopus lined up the rocks to form a wall in front of the den’s opening. Then it curled up inside. “That was my ‘aha’ moment,” remembers Mather. “Octopuses are smart!”

Since then, Mather has dedicated her life to studying how octopuses think. These creatures are thought to be among the world’s most intelligent invertebrates, or animals without backbones. Mather and others want to learn more about octopus smarts and how these animals’ sharp minds help them survive.

Since then, Mather has spent her life studying how octopuses think. Scientists believe octopuses are among the world’s most intelligent invertebrates, or animals without backbones. Mather and others want to learn more about octopus smarts. How do these animals’ sharp minds help them survive?

SURVIVAL SKILLS

About 300 species of octopuses live in oceans around the world. They make their homes in rocks and reefs, where they hunt crabs, fish, snails, and clams. The tiniest species, the star-sucker pygmy octopus, is smaller than a tennis ball. The largest, the giant Pacific octopus, can grow up to 6 m (20 ft) across from arm to arm. No matter the size, octopuses’ soft bodies make them tempting meals for predators like eels, sharks, and dolphins. “Everybody’s out to get them,” says Mather.

About 300 species of octopuses live in oceans around the world. They’re found in rocks and reefs, where they hunt crabs, fish, snails, and clams. The tiniest species is the star-sucker pygmy octopus. It’s smaller than a tennis ball. The largest is the giant Pacific octopus. It can grow up to 6 m (20 ft) across from arm to arm. Octopuses of all sizes have soft bodies, so predators like eels, sharks, and dolphins want to eat them. “Everybody’s out to get them,” says Mather. 

CHRIS NEWBERT/MINDEN PICTURES

TIGHT FIT: Octopuses can squeeze their bodies into extremely small spaces, like this jar.

As a result, octopuses have many adaptations to help them evade their enemies—like the extraordinary ability to change the color and texture of their skin. Octopuses’ talent for camouflage allows them to mimic other creatures or match their surroundings. The trick works so well that predators may swim by without even realizing there’s an octopus only a few feet away. Octopuses can also hide by squeezing their flexible bodies into tiny crevices. Despite its size, a full-grown giant Pacific octopus can fit through a hole no bigger than a lemon.

If there’s no hiding spot available, some octopuses make their own. In Indonesia, the veined octopus picks up broken coconut shells that fall into the water. It carries the pieces in its arms while moving from place to place along the sandy seafloor. If a predator approaches, the octopus pulls the shells over itself to hide (see Masters of Disguise). Few animals use natural objects as tools in such clever ways, says Piero Amodio, a biologist at the Stazione Zoologica Anton Dohrn in Naples, Italy. “It’s surprising how complex the behavior of octopuses can be,” he says.

So octopuses have many adaptations to help them avoid their enemies. For example, they can change the color and texture of their skin. That’s how they camouflage themselves to look like other creatures or match their surroundings. The trick works so well that predators may swim right by. They don’t even realize an octopus is a few feet away. Octopuses have another way to hide. They can squeeze their soft bodies into tiny openings. A full-grown giant Pacific octopus is huge, but it can fit through a hole as small as a lemon.

If no hiding spot is available, some octopuses make their own. In Indonesia, broken coconut shells fall into the water. The veined octopus picks them up. It carries the pieces in its arms when it moves along the sandy seafloor. If a predator approaches, the octopus pulls the shells over itself to hide (see Masters of Disguise). Few animals use natural objects as tools in such clever ways, says Piero Amodio. He’s a biologist at the Stazione Zoologica Anton Dohrn in Naples, Italy. “It’s surprising how complex the behavior of octopuses can be,” he says.

A DIFFERENT WAY OF THINKING

Scientists don’t all agree on what characteristics make an animal smart. But the ability to use tools, solve unfamiliar problems, and learn new skills are usually considered signs of intelligence. Researchers have observed these behaviors in chimpanzees, crows, and dolphins. All of these animals have large brains relative to their body size. The same is true for octopuses.

But in many ways, octopuses are unique among intelligent animals. Their nervous systems work differently from those of other smart species. In most intelligent animals, the brain contains the majority of the body’s neurons. These nerve cells transmit messages through the body and process information the senses take in. But only about one-third of an octopus’s neurons are in its brain. The rest are distributed among its arms (see Octopus Anatomy).

What makes an animal smart? Scientists don’t all agree. But some animals can use tools, solve unfamiliar problems, and learn new skills. These are usually considered signs of intelligence. Researchers have seen chimpanzees, crows, and dolphins do these things. All of these animals have large brains compared with their body size. So do octopuses. 

But octopuses are unlike other intelligent animals in many ways. For one thing, their nervous systems are different. In most intelligent animals, the brain contains the majority of the body’s neurons. These nerve cells send messages through the body. The senses take in information, and neurons process it. But only about one-third of an octopus’s neurons are in its brain. The rest are spread among its arms (see Octopus Anatomy).

PHOTO COURTESY OF D. SCHEEL

WELL HIDDEN: Jennifer Mather observes an octopus hiding among coral off an island in French Polynesia.

This unusual arrangement helps an octopus hunt, says Mather. The neurons in each arm control hundreds of sensitive suckers that line the appendages. An octopus uses its suckers to feel for and quickly grab hidden prey. The neurons allow each arm to react on its own, without waiting for instructions from the octopus’s brain.

Another thing that sets the octopus apart is that most intelligent animals live in groups. Evolving to have big brains likely helped these animals communicate and work together to survive. But octopuses spend almost all of their time alone, except for when they reproduce. That leaves scientists wondering how and why octopuses’ unusual intelligence developed over time.

This unusual setup helps an octopus hunt, says Mather. Hundreds of sensitive suckers line the arms. The neurons in each arm control the suckers. An octopus uses its suckers to feel for and quickly grab hidden prey. The neurons also allow each arm to react on its own. It doesn’t have to wait for instructions from the octopus’s brain. 

Another thing sets the octopus apart. Most intelligent animals live in groups. Evolving to have big brains likely helped these animals communicate and work together to survive. But octopuses are almost always alone. They get together only to reproduce. So scientists wonder: How and why did octopuses’ unusual intelligence develop over time? 

LEARNING CURVE

Octopuses are born knowing how to perform certain behaviors, like changing their looks to throw off predators, says Amodio. But some evidence suggests octopuses can also learn and make decisions. 

Octopuses know how to perform certain behaviors from birth, says Amodio. One example is changing their looks to throw off predators. But can octopuses also learn and make decisions? Some evidence suggests they can.

JORGEN JESSEN/AFP VIA GETTY IMAGES

GOOD GRIP: Octopuses can learn to unscrew jars to get a tasty treat inside.

As a graduate student, Amodio gave octopuses food inside sealed jars to see if the animals could open them. If they had watched another octopus do it, they figured out how to open the jars faster, showing they could learn new skills from one another. Amodio now designs puzzles to test whether octopuses can use unfamiliar objects as tools. In one ongoing experiment, he puts food on a platform above a tank and leaves a wooden rod near the octopus. If the octopus realizes it can use the rod to knock the food into the water, that shows the animal is capable of planning ahead.

Amodio enjoys the challenge of coming up with interesting problems for octopuses to solve. Their craftiness makes them fun to work with, he says. There’s still a lot left to discover about their intelligence, adds Mather. “We hardly know anything about them.”

Amodio studied octopuses as a graduate student. He gave them food inside sealed jars. Then he waited to see if the animals could open them. If they had watched another octopus do it, they figured out how to open the jars faster. That showed they could learn new skills from one another. Now Amodio tests whether octopuses can use unfamiliar objects as tools. He designs puzzles to find out. In one experiment, he puts food on a platform above a tank. He leaves a wooden rod near the octopus. Then he sees if the octopus uses the rod to knock the food into the water. That shows the animal can plan ahead.

It’s tricky to come up with interesting problems for octopuses to solve. But Amodio enjoys the challenge. Their cleverness makes them fun to work with, he says. There’s still a lot left to discover about their intelligence, adds Mather. “We hardly know anything about them.”