What makes octopus blood blue?

Haemocyanin, a copper-based pigment

What is a pseudomorph?

A dark ink blob that looks roughly like a cephalopod

Common octopus

Octopus vulgaris

The common octopus (Octopus vulgaris) is a soft-bodied mollusc with eight arms that lives on rocky, sandy and muddy seabeds of the Mediterranean Sea and the eastern Atlantic, from southern England to West Africa. It spends the day in a den, hunts crabs and shellfish mostly at night, and can change the colour and texture of its skin in moments. Look-alike octopuses in the Americas, Australia and other regions were long given the same name, but scientists now treat several of them as separate species.

Also known as Pulpo (Spanish), Polpo (Italian), Polvo (Portuguese)

Common octopus abilities

3 kinds of colour organs
The common octopus changes the colour, pattern and bumpiness of its skin in moments, to blend in or to signal.
- Chromatophores open and close under direct nerve control, not hormones, so patterns can flicker across the skin.
- Beneath them, iridophores add shine and leucophores reflect white light.
- Skin bumps called papillae rise to copy rough rock or weed.
- In life, its colours range from yellow-brown and red-brown to dark brown or grey.
Sources [4, 10]
3 shapes of ink
When attacked, it squirts dark ink out of its siphon and slips away while the predator is confused.
- Ink is made in the ink sac, darkened by melanin and mixed with mucus from the funnel organ.
- Thin ink makes a smoke screen. Thicker, mucus-rich blobs called pseudomorphs look roughly like a cephalopod, like a decoy.
- Long, thin strings of ink are called ropes.
Sources [4, 9]
2.5× blood pressure when busy
To make a quick getaway, it fills its mantle with water and squirts it out through the siphon, shooting backwards.
- Octopuses crawl on their arms, and they can jet when they need a fast escape.
- Jetting is hard work: pressure in the main artery rises from about 40 cm of water at rest to 100 cm or more during exercise.
- The main heart hardly speeds up. Instead, it pumps more blood with each beat.
Sources [4, 6, 11]
0 bones
With no skeleton, an octopus can pour its soft body into a crack and vanish into its den.
- Its old mollusc shell is reduced to two tiny rods (stylets), so the beak is the main hard part that has to fit through.
- Common octopuses choose dens in rock cracks or make them in sand and mud, and change them, for example with stones and shells.
- Staying in a den keeps them safer from predators such as groupers, wrasses, eels and sharks.
Sources [4, 13]
220–320 suckers per arm
An octopus explores cracks with its arm tips and tastes what it touches, so it can find a hidden crab without seeing it.
- Young common octopuses hunt mainly by feeling and tasting in crevices and under rocks, and they prefer crabs.
- Adults also wrap a rock in their arms and web, then use the arm tips to find and flush out prey.
- In the California two-spot octopus, sucker cells carry chemotactile receptors that detect chemicals on surfaces, such as on prey.
- About 300 million of its 500 million nerve cells are in the arms, which helps each arm work partly on its own.
Where the nerve cells are
Arms≈300 million
Optic lobes≈130 million
Rest of the brain≈40 million
Counts for the common octopus. Together they make roughly 500 million.
Sources [4, 5, 6, 8, 14]
3 hearts
Peek inside: three hearts, blue blood, a ring-shaped brain, a hard beak and an ink sac.
- One main heart pumps blood round the body, and two gill hearts push it through the gills.
- The blood is blue because of haemocyanin, a copper-based pigment that carries oxygen.
- The brain wraps around the gullet like a ring.
- The ink sac is tucked against the digestive gland. Its duct joins the gut, and the ink leaves through the siphon.
Sources [4]
up to 500,000 eggs in one brood
A mother octopus hangs strings of eggs from the roof of her den and looks after them until they hatch.
- She lays 100,000 to 500,000 eggs, each about 2 mm long, in strings called festoons.
- She blows fresh water over them and strokes them to keep algae and germs off, for up to 4–5 months in cool water.
- She usually does not eat during this time and can lose a third or more of her weight. It is her only brood: she reaches the end of her life around the time the young hatch.
- Studies of another octopus species suggest that hormones from small glands near the eyes, the optic glands, switch on this last stage of life.
Sources [4, 15]
weeks–months to regrow an arm
If an arm is badly damaged or lost, a common octopus can grow a new one, with muscles and nerves.
- A lost arm grows back within weeks to months.
- Scientists have studied regrowth in cephalopods for over 160 years, in more than 100 studies.
- The common octopus is a model animal for this research, and microscopes are used to follow how the new arm forms.
- Unlike some octopuses, it has no built-in breaking point for dropping an arm on purpose.
Sources [4, 16, 17]

Tap a pin on the model or a part below.

1 type of light-sensing cell
- Each eye has a horizontal, slit-shaped pupil.
- The eyes have only one type of light-sensing cell. In tests, common octopuses told shades apart by brightness, but not by colour.
- Octopuses can detect polarised light, which may help them spot prey or predators in sunlit water.
Sources [1, 2, 3, 4]
≈500 million nerve cells in all
- The brain is a ring around the gullet (oesophagus), so swallowed food passes through the middle of it.
- About 130 million nerve cells sit in the two optic lobes behind the eyes, and only about 40 million in the rest of the brain.
- Counting the arms too, a common octopus has about 500 million nerve cells, and about 300 million of them are in the arms.
- Scientists think the strong beak and toothed tongue may have evolved because food must pass through the brain ring in small pieces.
Sources [4, 5]
4–5½× as long as the mantle
- Eight arms, each 4 to 5½ times as long as the mantle. The third pair is usually the longest.
- A web of skin joins the arm bases.
- About 300 million nerve cells run through the arms, so each arm handles much of its own movement and touch.
- In males, the third right arm is a little shorter, with a special tip used for mating.
Sources [4, 5, 6]
220–320 suckers per arm
- Two rows of suckers run under each arm: about 220 to 320 per arm in a large octopus, or roughly 2,000 in all.
- Two or three suckers on the side arms are extra large, more so in males.
- Suckers grip wet and even rough surfaces, because their soft tissue moulds to the shape of the surface.
- Suckers also taste what they touch. In a close relative, the California two-spot octopus, scientists found “taste-by-touch” receptors in sucker cells.
Sources [4, 7, 8]
2 jobs jetting and inking
- The siphon (funnel) is a tube that sticks out of the opening of the mantle, under the head.
- Squirting water hard out of the siphon shoots the octopus backwards: jet propulsion.
- Ink from the ink sac leaves through the siphon too.
- Even 1–2 mm hatchlings swim by jet propulsion.
Sources [4, 9]
3 kinds of colour organs
- The skin has three kinds of colour organs: chromatophores (yellow, orange, red, brown and black pigment sacs), shiny iridophores and white leucophores.
- Each chromatophore is an elastic pigment sac pulled open by tiny muscles that are wired to the brain. That is why colours can change so fast.
- The common octopus can raise four large skin bumps (papillae) in a diamond on its back, and one or two over each eye.
- A pair of white spots on the back of the mantle is a common-octopus feature.
Sources [4, 10]
3 hearts
- Three hearts: one main (systemic) heart pumps blood round the body, and two gill hearts push blood through the gills.
- The blood is blue because it carries oxygen with haemocyanin, a copper-based pigment.
- At rest, the main heart of a 500 g common octopus beats about 40–50 times a minute (at 22 °C). When the octopus is busy, the heart pumps more blood per beat rather than beating much faster.
Sources [4, 11]
1 big hard part in the body
- In the middle, under the arms, is a hard, parrot-like beak made of chitin, plus a toothed tongue called a radula.
- Its saliva contains toxins and enzymes that quickly calm crabs and fish and start to digest them.
- To get into shellfish, it can drill a tiny hole with toothed bumps near the radula and soften the shell with saliva.
- There is no skeleton, and the old mollusc shell is reduced to two tiny rods. That leaves the beak as the main hard part.
Sources [4, 12]
By day time spent in the den
- Common octopuses spend most of the day in a den: a crack in the rocks, or a hollow they make in sand or mud, sometimes with stones and shells.
- On soft seabeds, a shortage of den-building material can limit where they live.
- Shells and crab remains pile up outside as a midden. But young octopuses eat about 30% of their prey away from home, and waves wash small remains away.
- They are mostly active at night, from the shore down to about 250 m, but usually in water shallower than 100 m.
Sources [4, 13, 14]

Real common octopuses

Photos from Wikimedia Commons, all from the Mediterranean and eastern Atlantic, where Octopus vulgaris lives. One shows a mother with her eggs.

Hiding in a rock crack near Plakias, Crete, GreecePhoto: Martijn Klijnstra, CC BY-SA 4.0
Mother with eggsA female in her den, with strings of tiny eggs hanging from the roof. She stays with them for weeks or months.Her one and only broodA mother octopus with her eggs. Photo: Ruggero Caravita, CC BY-SA 3.0
An eye up closePhoto: Federico Stefanelli, CC BY-SA 4.0
Medes Islands marine reserve, Costa Brava, SpainPhoto: Jouni Kuisma, DiveCodex, CC BY-SA 4.0
Moneglia, Liguria, ItalyPhoto: Holger Krisp, CC BY 4.0
Blue Lagoon, Akamas Peninsula, CyprusPhoto: Ansgar Gruber, CC BY-SA 2.0
Cathedral Cave, Gozo, MaltaPhoto: Diego Delso, CC BY-SA 4.0
Arrábida, Atlantic coast of PortugalPhoto: Diego Delso, CC BY-SA 4.0
Teno-Rasca, Tenerife, Canary IslandsPhoto: Diego Delso, CC BY-SA 4.0

Common octopus by the numbers

Measured by scientists and fishery experts, mostly from the FAO’s species catalogue.

Mantle length: up to 40 cm; commonly about 25 cm⁠[4]
Total length: ≈1.8 m max; the arms are 4–5½ times as long as the mantle⁠[4]
Weight: over 20 kg; the largest known; most are much smaller⁠[4]
Suckers: 220–320 per arm; in two rows, in larger animals; Roughly 2,000 suckers in all⁠[4]
Nerve cells: ≈500 million; about 300 million of them in the arms; 3 out of every 5 are in the arms⁠[5]
Hearts: 3; 1 main heart and 2 gill hearts, pumping blue blood⁠[4]
Resting heartbeat: 40–50 per min; a 500 g octopus at 22 °C⁠[11]
Eggs per brood: 100,000–500,000; each about 2 mm long⁠[4]
Lifespan: 1–2 years; females breed once⁠[4]
Depth: 0–250 m; usually shallower than 100 m⁠[4]

Common octopus: myth or fact?

Octopuses attract tall tales. Here is what the evidence says.

0 of 8 answered

“An octopus has eight tentacles.”
“Octopuses have three hearts and blue blood.”
“An octopus has nine brains.”
“Octopuses see the colours they copy.”
“The common octopus carries coconut shells to hide in.”
“The common octopus disguises itself as a sea snake or a lionfish.”
“An octopus can open a jar to get the crab inside.”
“The common octopus lives in oceans all over the world.”

Common octopus records

Big numbers and record holders, each checked against its source.

World’s biggest one-species octopus fishery
≈58,000 t
Common octopus off northwest Africa
Africa’s octopus catch in 2010, almost all of it this species; Morocco landed about 32,000 t⁠[4]
Biggest egg brood
up to 500,000
Common octopus mother
eggs in strings on the roof of her den⁠[4]
Longest guard duty
up to 4–5 months
Common octopus mother
guarding her eggs without feeding, in cool water⁠[4]
Nerve cells outside the brain
≈300 million
Common octopus arms
3 in every 5 of its nerve cells are in the arms⁠[5]
Biggest on record
over 20 kg
Common octopus
with a total length of up to about 1.8 m⁠[4]
Sucker count
≈2,000
Common octopus
220–320 suckers on each arm of a large octopus⁠[4]

A common octopus’s life

From a 2 mm egg to a seabed hunter and parent in just one or two years.

Day 0
An egg on a string
The mother hangs her eggs, each about 2 mm long, in strings from the roof of her den.⁠[4]
Weeks to months
Guarded
She cleans the eggs and blows fresh water over them. They hatch faster in warm water and can take 4–5 months in cool water.⁠[4]
Hatching
A tiny drifter
Hatchlings are 1–2 mm long and see-through, with short arms and few suckers. They swim straight up into open water as plankton.⁠[4]
Weeks to months
Night swimmer
The young (paralarvae) jet about, rise towards the surface at night, stay deeper by day and eat young crustaceans.⁠[4]
Settling
Down to the seabed
They settle, change into a small adult shape with many suckers and patterned skin, and start a hidden life on the seabed.⁠[4]
Growing up
Den and dinner
Young octopuses find dens and hunt crabs and shellfish by touch and taste, mostly at night.⁠[4, 14]
About 1 year
Grown up
Adults mate with several partners, and there are no couples. A female keeps the male’s sperm packets until she is ready to lay her eggs.⁠[4]
1–2 years
A short life
A mother stops eating while she guards her eggs and dies around the time they hatch. Common octopuses live about 1–2 years.⁠[4]

How the common octopus hides

Colour-blind eyes, yet some of the best camouflage in the sea. These are the parts that make it work.

3
kinds of colour organs
Chromatophores hold yellow, orange, red, brown or black pigment. Iridophores add shine, and leucophores reflect white light.⁠[4]
Nerves
not hormones
Each chromatophore is opened by tiny muscles wired to the brain, so patterns can change very fast and very finely.⁠[10]
4
big bumps on the back
Four large papillae in a diamond on the back, plus one or two over each eye, can be raised to copy rough rock and weed.⁠[4]
1
type of light-sensing cell in the eye
In tests, octopuses tell shades apart by brightness, not colour. Their camouflage seems to match brightness and pattern rather than exact colours.⁠[4, 2, 3, 1]
Skin
that senses light
Skin of the California two-spot octopus reacts to light by itself, and a light-sensing gene is active in common octopus suckers and skin. How much this helps camouflage is not yet known.⁠[26, 27]

One idea, from a computer model, is that the octopus’s slit pupil could let it pick up colour from tiny differences in blur. It has not been shown in living octopuses.

Common octopus vs squid vs cuttlefish

All three are cephalopods with ink and big brains, but their bodies are built differently.

Common octopus vs squid vs cuttlefish
	Common octopus	Squid	Cuttlefish
Arms and tentacles⁠[4, 19]	8 arms	8 arms + 2 long feeding tentacles	8 arms + 2 long feeding tentacles
Shell inside⁠[4, 19]	None, or 2 tiny rods (stylets)	Usually a thin pen (gladius)	A chambered shell (cuttlebone)
Suckers⁠[4, 19]	Sit right on the arm	On stalks, with horny rings	On stalks, with horny rings
Pupil shape⁠[1]	Horizontal slit	U-shaped (shallow-water squids)	U-shaped
Eggs⁠[4]	Mother guards and cleans them	Wrapped in jelly	Wrapped in jelly
Ink⁠[9]	Yes	Yes	Yes

The squid and cuttlefish columns describe each group in general; individual species vary.

Is the common octopus endangered?

No. It is widespread and common, but it is also one of the most heavily fished octopuses in the world.

IUCN Red List

Least Concern (LC)

Trend unknown

Common in the Mediterranean and eastern Atlantic. Numbers can rise and fall a lot from year to year.⁠[28, 29, 4]

IUCN Red List (via Wikidata and GBIF)

Threats

Heavy fishing≈58,000 t
It is caught by everyone from hobby fishers to big fleets. Off northwest Africa it supports the world’s largest single-species octopus fishery, where falling catches have been reported.⁠[4]
Boom-and-bust years
Babies drift as plankton for weeks or months, so currents and sea conditions strongly affect how many young octopuses arrive each year.⁠[4]

What’s helping

Counted as sentient2022
The UK’s Animal Welfare (Sentience) Act 2022 includes all cephalopods, such as octopuses, in its definition of animals.⁠[30]
The farming debate2024
Because the common octopus is so valuable, researchers and companies, especially in Spain, have worked on farming it, although raising the tiny hatchlings has proved hard. Some scientists argue against octopus farming, because octopuses eat other animals and are behaviourally complex. In 2024, Washington State in the USA banned octopus farming.⁠[4, 31, 32, 33]

Common octopus quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

How many hearts does a common octopus have?

Common octopus field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

Octopuses are clever predators, feasting on crabs, clams, and small fish in the ocean.

Primary Foods

crabs
lobsters
clams
snails
small fish
Foraging Method: Foraging

Ecological connections

Tiger SharkEaten by
Sharks are among the predators of octopuses.
Bottlenose DolphinEaten by
Dolphins hunt octopuses.
Mediterranean MorayEaten by
Moray eels are skilled octopus hunters.

Safety

Danger 2/5 · Low

Always observe octopuses from a safe distance and never touch them in the wild.

Traits

Collections

Invertebrates

Classification

Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Octopoda
Family: Octopodidae
Genus: Octopus

Also known as

Pulpo (Spanish) · Polpo (Italian) · Polvo (Portuguese) · Pieuvre (French) · Gemeiner Krake (German) · Chtapodi (Greek) · European Octopus

Sources for these common octopus facts

35 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Common octopus?

Look for fins, arms, tentacles, shells and body symmetry. Underwater light shifts colors, so structure and markings usually matter more than shade. Sea Creature Identifier: upload a photo and compare the visible details.

How big is Common octopus?

30 cm

How much does Common octopus weigh?

5 kg

How long does Common octopus live?

1 years

What does Common octopus eat?

Octopuses are clever predators, feasting on crabs, clams, and small fish in the ocean.

Where is Common octopus usually found?

Marine

How many arms does Common octopus have?

How many hearts does an octopus have?

Three. Two gill hearts pump blood through the gills, and one main heart pumps it round the body. At rest, the main heart of a 500 g common octopus beats about 40–50 times a minute.

How smart is the common octopus?

Very good at solving practical problems. In lab tests, common octopuses learned to pull the plug out of a glass jar to reach a crab and got faster with practice. A famous 1992 study found that octopuses that watched a trained octopus then picked the same ball (red or white), but it was a single study, and scientists still discuss how much octopuses learn by watching. Using coconut shells as shelters was seen in a different species, the veined octopus.

How many suckers does a common octopus have?

A large common octopus has about 220–320 suckers in two rows on each arm, roughly 2,000 in all. The suckers grip wet, rough rock and can taste what they touch.

Can octopuses see colour?

Probably not. Their eyes have only one type of light-sensing cell, and in tests common octopuses told shades apart by brightness, not colour. Scientists are still working out how they match their surroundings so well; their skin may sense light too.

How long does a common octopus live?

About 1–2 years. Females breed only once: a mother guards her eggs for weeks or months, stops eating, and dies around the time they hatch.

Is the common octopus dangerous to humans?

No. Like other octopuses it has venomous saliva for subduing crabs and fish, but it is not dangerous to people. Bites are rare and usually happen when someone handles a freshly caught octopus. A bite can hurt and, rarely, get infected, so tell an adult and see a doctor. Never touch octopuses in the wild: blue-ringed octopuses carry a toxin that has killed people.

Where does the common octopus live?

Octopus vulgaris lives in the Mediterranean Sea and the eastern Atlantic, from the south coast of England to West Africa, the Azores, the Canary Islands and Cape Verde. It lives on rocky, sandy or muddy seabeds from the shore to about 250 m deep. Similar octopuses elsewhere are now treated as separate species.

How does a common octopus hunt?

Mostly at night. It probes cracks and the spaces under rocks with its arms, or wraps a rock in its arms and web and flushes out prey with its arm tips. It catches crabs, lobsters, fish and shellfish, and can drill or prise shells open.