Octopus Facts

An octopus runs on hardware built for a boneless life in cold water. It has three hearts — two pump blood through the gills, one drives it round the body — and its blood is blue because it carries oxygen with a copper-based protein, hemocyanin, which works well in cold, low-oxygen water. With no skeleton, the body is a hydrostatic system of muscle working against fluid, so it can squeeze through any gap wider than its beak. Most striking is the nervous system: of roughly half a billion neurons, about two-thirds lie in the eight arms, which can taste and feel through their suckers and carry out complex movements semi-independently of the central brain.

Octopus vulgaris is a strictly marine, bottom-dwelling species of shallow coastal waters in the eastern Atlantic and the Mediterranean, along the coasts of Europe and Africa. It concentrates on structured ground — rocky reefs, coral, seagrass, and kelp — because it needs a supply of caves, crevices, and debris to build the protective "den" it retreats to. It depends on stable, full-strength seawater and cannot tolerate big swings in water chemistry.

The octopus is a carnivore that hunts mostly at night, living largely on crustaceans (crabs, lobsters, shrimp), bivalves (clams, mussels), and small fish. It combines stealth with touch, often "speculative hunting" — pushing its flexible arms into dark crevices to flush hidden prey — then pouncing and wrapping the victim in the web between its arms. To open armoured prey it uses a hard, parrot-like beak at the centre of its arms and a toothed ribbon called a radula, drilling through shells with the help of acidic saliva, and it injects a paralysing venom to subdue prey quickly.

The octopus's defining skill is instant disguise. Its skin holds millions of pigment cells (chromatophores) over reflective and light-scattering layers, all under nerve control, so it can change colour and pattern in a fraction of a second — and muscular bumps called papillae let it change the skin's texture too, matching rock, coral, or algae. Its intelligence is equally notable: in the lab octopuses solve mazes, remember, and unscrew jars or take apart aquarium fittings. When camouflage fails, it escapes by jet propulsion — firing water through a siphon — behind a cloud of ink that both hides it and dulls a predator's sense of smell. Otherwise it is solitary and territorial, and will cannibalise smaller octopuses.

The octopus breeds only once and then dies (semelparity). A male uses a specialised arm, the hectocotylus, to pass sperm packets into the female, then declines and dies soon after. The female lays tens of thousands of tiny eggs in braided strings on a den ceiling and guards them for weeks to months — fanning them with her siphon to keep them oxygenated and cleaning off fungus — while eating nothing at all. As the young hatch as tiny drifting paralarvae, the starved, exhausted mother dies. The whole life lasts just 1 to 2 years.

The common octopus is Least Concern; its fast growth, huge egg output, and short generations make populations resilient. Its natural predators include moray and conger eels, dolphins, large fish, and sharks, and it is heavily targeted by fisheries across the Mediterranean and coastal Africa using traps, pots, and trawls. Populations are broadly stable, but localised overfishing needs management, and reliance on stable seawater leaves the species exposed over the long term to ocean warming and acidification, which can hit larval survival.

• IUCN Red List of Threatened Species: Octopus vulgaris
• National Geographic: Common Octopus
• Oceana: Common Octopus
• Marine Biological Association: Octopus vulgaris