Octopuses — The Smartest Creatures in the Sea

If you wanted to design an animal that looked like an alien, you might come up with something very similar to an octopus. They have eight flexible arms covered in hundreds of suckers. They have no bones at all — their entire body is soft, which means they can squeeze through gaps as small as a coin. They have three hearts — two pump blood to their gills, and one pumps blood to the rest of their body. And their blood is blue, not red, because it uses copper instead of iron to carry oxygen.

There are more than 300 species of octopus, and they live in every ocean in the world — from warm tropical reefs to the freezing waters of the Arctic and Antarctic. The smallest species is barely 2 centimetres long. The largest, the giant Pacific octopus, can have an arm span of more than 4 metres and weigh up to 50 kilograms.

Octopuses are masters of camouflage. They can change the colour, pattern, and even the texture of their skin in less than a second. They do this using special cells called chromatophores, which contain tiny bags of pigment that can be expanded or contracted by muscles. An octopus sitting on a rock can make itself look exactly like that rock — matching not just the colour but the bumpy texture of the surface.

Some species can do even more. The mimic octopus, found in Southeast Asian waters, can change its body shape to imitate other animals — including lionfish, flatfish, and sea snakes. It is the only animal known to impersonate multiple other species, and scientists are still not sure how it decides which animal to copy in any given situation.

For a long time, scientists believed that only animals with large brains and backbones — mammals and birds — could be truly intelligent. Octopuses have completely destroyed this assumption. Despite being invertebrates with a brain very different from ours, they have demonstrated levels of intelligence that continue to astonish researchers.

Octopuses can solve complex puzzles. In laboratory experiments, they have learned to unscrew jars from the inside to escape, navigate mazes to reach food, and even open childproof containers. One famous octopus named Inky, held at the National Aquarium of New Zealand, escaped from his tank in 2016 by squeezing through a small gap, crawling across the floor, and sliding down a drainpipe that led to the ocean. He was never seen again.

Perhaps most remarkably, octopuses can use tools. They have been observed carrying coconut shell halves across the ocean floor and assembling them into shelters — picking up one half, walking to another location, finding a second half, and then climbing inside and pulling the two halves together. Tool use was once considered a uniquely human ability, then it was found in great apes, then in crows, and now in an animal with no backbone.

In 2025, researchers at Dartmouth College published a study showing that octopuses could learn to use mirrors to find hidden food — a cognitive ability previously thought impossible for invertebrates. The octopuses were not just using their reflection to groom themselves, as some animals do, but were using the mirror as a tool to see around corners and locate rewards they could not see directly. This discovery sent shockwaves through the scientific community.

What makes octopus intelligence so fascinating to scientists is not just that they are smart, but how they are smart. An octopus brain is completely different from a human brain — or any mammal brain — in structure and organisation. Understanding how octopuses think is helping scientists answer one of the biggest questions in biology: is there more than one way to build a mind?

Humans have about 86 billion neurons — the cells that carry electrical signals in the brain and nervous system. An octopus has about 500 million neurons, which is far fewer than a human but more than most other invertebrates. What is truly unusual is where these neurons are located. In a human, almost all neurons are in the brain. In an octopus, about two-thirds of the neurons are in the arms — not in the brain.

This means that each arm can taste, touch, and to some extent think independently. If an octopus arm is cut off — which can happen during a fight with a predator — the severed arm can continue to react to its environment for several hours, grasping objects and responding to stimuli. Each arm is, in a sense, a semi-independent creature with its own basic intelligence.

This distributed intelligence — spread across the body rather than centralised in the brain — is completely different from how mammalian intelligence works. It suggests that intelligence is not a single thing that requires a specific type of brain. Instead, it may be a general solution that evolution can arrive at through many different routes. The octopus is proof that you do not need a brain like ours to be smart — you just need a brain that works.

As scientists learn more about how intelligent octopuses are, a difficult ethical question is growing louder: should we treat them differently from other sea creatures?

Currently, octopuses are eaten in large quantities around the world. In Japan, South Korea, Spain, Portugal, and many other countries, octopus is a popular and traditional food. Global demand for octopus has been rising for years, and in 2023, a company in Spain announced plans to build the world's first commercial octopus farm. The proposal caused an immediate outcry from animal welfare organisations, who argued that farming an animal of such proven intelligence was morally wrong.

The UK became the first country to officially recognise octopuses as sentient beings — creatures capable of feeling pain and emotions — when it passed the Animal Welfare (Sentience) Act in 2022. This law means that the welfare of octopuses must now be considered when making policy decisions in the UK. Several other countries are considering similar legislation.

The debate raises a fundamental question: does intelligence determine how we should treat an animal? We already accept that it is wrong to cause unnecessary suffering to dogs, cats, and other animals we consider intelligent. But we routinely farm and eat animals like chickens, pigs, and fish without the same moral concern — even though pigs, for example, are highly intelligent. Where should the line be drawn?

Octopuses live short lives — most species live only one to two years. They are solitary creatures that do not form social bonds. They do not care for their young. In many ways, they could not be more different from the social, long-lived mammals we find it easiest to empathise with. And yet their intelligence, their curiosity, and their apparent ability to experience the world in complex ways make the question of how we treat them increasingly difficult to ignore.