WHAT THE EVIDENCE SAYS

One brain,
eight clever arms.

The octopus is a very different kind of clever.

A common octopus resting on a rocky seabed in clear blue water, its arms curled around the stones — AI-generated image, not a photograph of a real person or place.

Most neurons in the arms
Learns by trial and error
Sentient in UK law
An isolated outpost of intelligence

It has about as many neurons as a dog, but most of them sit in its arms. Researchers have watched octopuses learn mazes and carry coconut shells as portable shelters, and UK law now counts them as sentient.

Updated 16 October 2026

THE SHORT ANSWER

Clever, but
built differently.

Octopus intelligence evolved apart from ours.
The evidence comes from labs, dives and a UK review.

NERVOUS SYSTEM

Thinking with the arms

OIST researchers say octopuses have over 500 million neurons, similar to a dog, with over two thirds of them in the arms and body rather than the brain.

See the numbers

TOOLS

Coconut-shell armour

Divers in a 2009 study saw veined octopuses stack coconut shell halves and carry them up to 20 metres to use later as a shelter.

What they can do

THE LAW

Sentient since 2022

The Animal Welfare (Sentience) Act 2022 counts every cephalopod mollusc, including octopuses, squid and cuttlefish, as a sentient animal.

Compare the evidence

COMPARE THE EVIDENCE

How strong is the
case for feeling?

Pick an animal group to see how the 2021 LSE review graded the evidence that it is sentient: able to experience pain, distress or harm.

Grades from the LSE Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans (November 2021).

Sentience evidence

Choose an animal groupOctopusesTrue crabsSquid and cuttlefishLobsters and crayfishInsects

OctopusesVery strong

High or very high confidence on seven of the review's eight criteria, and medium confidence on the eighth.

True crabsStrong

High or very high confidence on five criteria, including pain-sensing nerves and learning.

Squid and cuttlefishSubstantial

Less evidence than for octopuses, but still substantial. The review notes that less-studied groups score lower partly because less research exists.

Lobsters and crayfishSubstantial

Substantial evidence for astacid lobsters and crayfish. The review recommended that all decapods be treated as sentient.

InsectsNot covered

Outside this review and outside the 2022 Act, which covers vertebrates, cephalopods and decapods. Ministers can add other invertebrates by regulations.

Sources: LSE review (2021), foreword and executive summary; Animal Welfare (Sentience) Act 2022, section 5. The grades describe evidence of sentience, not intelligence.

TWO NUMBERS WORTH KNOWING

A big nervous system,
a big body of evidence.

One figure on the octopus itself,
one on how much research the UK review weighed.

500 million+

Neurons in an octopus

Similar in number to a dog's. Unlike in dogs and other vertebrates, over two thirds of an octopus's neurons sit in its arms and body, not its brain.

NEURONS · OIST

300+ studies

Scientific publications assessed

The government-commissioned LSE review judged over 300 publications against eight criteria, from pain-sensing nerves to learning.

UK REVIEW · LSE 2021

Each octopus arm carries over 200 suckers that can feel, taste and smell, according to an OIST researcher.

An octopus tucked inside a half coconut shell on a sandy seabed, peering out — AI-generated image, not a photograph of a real person or place.

FOUR THINGS OCTOPUSES HAVE SHOWN

Smarts you can
see in action.

These come from experiments and field observations, not anecdotes. Each shows a different side of how an octopus solves problems.

Learning a hidden maze
In an OIST study, five of six octopuses learned which side of an opaque Y-shaped maze held food, using an arm they could not see.
Carrying portable shelter
Veined octopuses collected coconut shell halves, stacked them and walked them across the seafloor for later use as a lair.
Escaping and opening jars
Researchers describe octopuses opening jars, solving puzzles and even escaping from their tanks.
Decorating the den
A Harvard report notes octopuses often gather debris such as broken glass and tiles and place it in front of their dens.

A SEPARATE EXPERIMENT IN MINDS

Our last shared
ancestor was ancient.

Dolphins, chimpanzees, elephants and clever birds are all vertebrates, relatively close relatives of ours. Octopuses are invertebrates, and our last common ancestor lived 500 to 600 million years ago.

That means octopus intelligence probably evolved entirely separately from ours, which is why researchers study it to ask which features of a mind are universal and which are unique to us.

Close-up of an octopus arm curling over a smooth grey stone, showing its rows of suckers — AI-generated image, not a photograph of a real person or place.

Questions

Questions people ask

Do octopuses have nine brains?

Not quite. Some scientists have described them that way, but a 2020 OIST study found information flows between the arms and the central brain, and the researcher behind it described one brain and eight very clever arms.

How many neurons does an octopus have?

Over 500 million, similar to a dog, according to OIST. More than two thirds are in the arms and body.

Are octopuses legally sentient in the UK?

Yes. The Animal Welfare (Sentience) Act 2022 defines animal to include any vertebrate other than humans, any cephalopod mollusc and any decapod crustacean.

Did that change fishing or restaurants?

The government said in 2021 that existing industry practices would not be affected. The law also provides for an Animal Sentience Committee to report on how well government policy takes account of animal welfare.

Do octopuses use tools?

A 2009 study described veined octopuses carrying stacked coconut shell halves up to 20 metres and using them later as shelter, which the researchers counted as tool use.

One brain,
eight clever arms.