Common Octopus — facts, diet, habitat & conservation

The common octopus is the animal that most challenges our idea of what a mind looks like. It is a mollusc — more closely related to a garden snail than to a fish — yet it solves problems, uses tools, and appears to be curious about the world, all with a body that is almost entirely soft and a life that lasts barely two years.

Overview

Octopus vulgaris is found in warm and temperate coastal seas around the world, on reefs, rocky bottoms, seagrass beds, and sandy flats from the tide line down to about 200 m. It is a solitary ambush predator that spends the day in a den — a crevice, a shell, a discarded bottle — surrounded by a tell-tale pile of empty crab and clam shells called a midden.

An alien body plan

Everything about the octopus is a different solution to being an animal:

Eight arms, each lined with up to 240 suckers that grip, taste, and manipulate. There is no central “the octopus decides”; roughly two-thirds of its 500 million neurons sit in the arms, which explore and react on their own.
Three hearts. Two pump deoxygenated blood through the gills; the third sends the oxygenated blood around the body. That third heart stops when the octopus swims, which is part of why it prefers to crawl.
Blue blood. Oxygen is carried by haemocyanin, a copper-based molecule that works better than iron-based haemoglobin in cold, low-oxygen water.
No bones. The only hard part is a parrot-like beak. An octopus the size of a football can pour itself through a hole the width of a coin.

Camouflage and defence

The octopus is the ocean’s fastest quick-change artist. Its skin holds millions of chromatophores — pigment sacs it opens and closes with muscles under nerve control — over layers of reflective cells, letting it match colour, pattern, brightness, and even skin texture to its background in a fraction of a second. Strangely, octopuses are colour-blind; how they colour-match so well is still debated.

When camouflage fails it releases a cloud of ink, jets away by forcing water through a muscular funnel, and can drop an arm as a writhing decoy — the arm grows back.

Hunting and intelligence

The octopus hunts crabs, clams, snails, and fish. It pounces and enfolds prey in its arm web, then either bites through the shell with its beak, drills a neat hole and injects a paralysing, digestive saliva, or simply pulls a bivalve apart. It caches food and returns to it.

In captivity octopuses open child-proof jars, complete mazes, distinguish and remember individual keepers, and have been filmed carrying halved coconut shells to reassemble later as armour — one of the clearest cases of tool use in an invertebrate. Give one an unfamiliar object and it will handle and probe it, apparently for its own sake.

Reproduction and the short life

The common octopus lives fast. A female lays up to 200,000 eggs in strings hung from the roof of her den. She then stops hunting, spending weeks or months cleaning the eggs and blowing fresh water over them. By the time they hatch she is starving and dies soon after; the male has usually died months earlier. The tiny hatchlings drift as plankton before settling to the seafloor, and only a handful from each clutch survive to adulthood.

This single-shot life cycle — controlled by hormones from a gland behind the eyes — means populations turn over completely every year or two and can rebound quickly, but also crash quickly if conditions turn.

People and octopuses

The common octopus is one of the most heavily fished cephalopods in the world, especially around the Mediterranean, West Africa, and Japan. It is listed as Least Concern because it is widespread and fast-breeding, but individual fisheries can be overexploited, and warming, acidifying seas are already shifting where the species can live. Its intelligence has also put it at the centre of an ethical debate over proposals to farm octopuses commercially.

Common Octopus: common questions

How does an octopus change colour so fast?

Its skin contains millions of pigment sacs called chromatophores, each ringed by tiny muscles. The octopus expands or contracts them under direct nerve control to shift colour and pattern in well under a second. Layers of reflecting cells beneath add shimmer and iridescence, and it can also change the texture of its skin to match rock or coral.

Is an octopus intelligent?

Remarkably so, for an invertebrate. Octopuses learn by trial and error, remember solutions, open jars, navigate mazes, use coconut shells and rocks as portable shelter and tools, and recognise individual people. Much of that processing happens in the arms, each of which has its own bundle of nerve cells and can taste, touch, and react semi-independently.

Why do octopuses die so young?

They are "semelparous" — they breed once, then die. After mating, the male declines within months. The female stops eating to guard and aerate her eggs, and by the time they hatch she has starved. A gland behind the eyes controls this self-destruct cycle; removing it in experiments lets the female live longer.

How does an octopus escape predators?

It has a full toolkit — camouflage to avoid being seen at all, a cloud of dark ink to blind a pursuer and dull its sense of smell, jet propulsion by firing water through a funnel, the ability to squeeze its boneless body through any gap wider than its beak, and, as a last resort, detaching an arm that keeps wriggling as a decoy. The arm regrows.