Top 7 Things You Didn't Know About Octopuses

An octopus has no rigid internal skeleton, so much of its body can deform to fit through narrow spaces. That makes it an extraordinary escape artist: a gap that looks far too small for the animal may be perfectly passable. There is, however, one important limitation. Its beak—the hard, parrot-like structure used to bite and break up food—is a key constraint. If the beak cannot pass through the opening, the rest of the body cannot follow. The size of the gap an octopus can manage depends on the species and the animal’s size, so there is no single measurement that applies to every octopus. This flexible anatomy is useful when navigating reefs and rocky habitats, but it also explains why keeping an octopus securely in an aquarium can be surprisingly difficult.

An octopus does not rely on its mouth to investigate food. Its suckers contain specialised sensory cells that respond to both touch and certain chemicals, giving the arms a form of contact-based chemical sensing often described as taste by touch. Research published in Cell in 2020 identified receptors that help octopus suckers detect naturally occurring substances, including compounds that do not dissolve readily in water. This means an arm can explore a surface and gather information about it as it moves, rather than simply acting as a limb that carries information back to the head. Octopuses also have a highly distributed nervous system, with substantial neural processing in their arms. That does not mean each arm is an entirely independent mind, but it does help explain how an animal with eight flexible arms can investigate its surroundings in such a coordinated, exploratory way.

Octopuses have demonstrated learning and problem-solving in controlled experiments. In one study, researchers tested common octopuses with a container that had to be manipulated to obtain food. In another, seven octopuses learned to retrieve an L-shaped container through a tight opening, then adapted as the task became more difficult. All seven eventually met the study’s success criteria. These experiments do not mean octopuses think exactly like humans, and researchers continue to investigate how they learn and which strategies they use. But they do show that their behaviour can be flexible rather than simply a fixed response to a stimulus. Tool use provides another striking example: coconut-carrying octopuses have been observed transporting shell halves and assembling them later as shelter. Carrying an awkward object that offers no immediate protection is a particularly intriguing behaviour, because its usefulness depends on what the animal does with it later.

When threatened, many octopuses release a cloud of dark ink and use the confusion to escape. It is often described as an underwater smoke screen, but that explanation can be incomplete. Depending on the circumstances, the released material may obscure the predator’s view or form a concentrated decoy that draws attention away from the fleeing animal. Scientists have also investigated whether chemical components of cephalopod ink can interfere with predators’ senses. Those possible chemical effects are not equally well established for every species or predator, so they should not be treated as a universal superpower. The basic defensive function, however, is clear: the ink can buy an octopus time to change direction and get away. It is one part of a broader escape strategy that can also involve camouflage, rapid movement and squeezing into a crevice. The octopus is not just hiding; it is creating an opportunity to escape.

An octopus has three hearts. Two branchial hearts pump blood through the gills, where it picks up oxygen; a third, systemic heart circulates oxygenated blood around the body. Its blood is blue because it uses a copper-containing oxygen-carrying protein called haemocyanin, rather than the iron-containing haemoglobin found in human blood. The most surprising detail is what happens during swimming: the systemic heart temporarily stops beating. This is associated with the considerable energetic cost of swimming and helps explain why octopuses often move by crawling along the seabed instead. The detail needs careful wording: the heart does not stop permanently, and the animal does not simply cease functioning when it swims. It is a distinctive feature of its circulatory system that makes a seemingly ordinary action—moving through water—more demanding than you might expect. Three hearts, blue blood and an energetically expensive swimming style make for a very unusual package.

For many octopus species, reproduction involves an extraordinary final commitment. After laying her eggs, a female may guard them for an extended period, keeping them clean and circulating water over them to help supply oxygen. During this brooding period, she may stop eating or reduce her food intake dramatically, leaving little energy for her own survival. In some species, the mother dies around the time her eggs hatch. Research on octopuses has linked this reproductive decline to changes involving the optic glands, which influence feeding and other behaviours after spawning. This is not a rule that should be applied without qualification to every species, and the details of egg care and lifespan vary. But the broader pattern is remarkable: in many octopuses, reproduction is closely tied to the end of the adult’s life. The next generation can emerge into the world as the mother’s life reaches its conclusion.