How do cuttlefish change colour so quickly?

The secret lies in the chromatophore organ. Each chromatophore consists of a small, elastic sac filled with pigment granules, surrounded by a ring of tiny radial muscles, like the spokes of a wheel. Each muscle is connected to nerve fibres that run directly from the brain. When the nerves fire, the muscles contract and pull outward on the sac, stretching it into a flat disc that spreads the pigment over a larger area of skin. When the nerves stop firing, the muscles relax, and the elastic sac shrinks back to a tiny dot.

Because the system is driven by muscles under direct nervous control, it is extremely fast. A cuttlefish can change from pale to dark, or from one pattern to another, in a fraction of a second. According to standard references, an expanded chromatophore can cover about five times the area it occupies when retracted, and there can be up to around 200 of them in each square millimetre of skin. Together, millions of chromatophores act like the pixels of a living display screen.

Where do the signals come from?

The commands for colour change come from the brain, specifically from regions called the chromatophore lobes, which contain the motor neurons that control the chromatophore muscles. These neurons receive input from higher brain centres that process vision and decide on behaviour. Each motor neuron may control a group of chromatophores, so that patterns are built from many small units switched on and off together.

This direct wiring is unusual in the animal world. In fish, amphibians and reptiles, colour cells called melanophores are mostly controlled by hormones or by slower nervous signals that move pigment inside the cells, which takes seconds to minutes. Chameleons change colour mainly by adjusting the spacing of tiny crystals in their skin cells, which alters the colours they reflect. Cephalopods, by contrast, use muscles, giving them speed and precision that no other animals match.

What are the different layers of colour cells?

Cuttlefish skin is layered. Near the surface lie the chromatophores, in three colours: yellow to orange at the top, red in the middle and brown to black deepest down. Below them are iridophores, cells containing stacks of thin plates that reflect light to produce iridescent blues, greens and pinks. Deepest are leucophores, which scatter white light. In some places, the layers are arranged so that a white leucophore patch sits directly under a group of chromatophores.

Only the chromatophores are directly controlled by muscles. The reflective cells beneath them are mostly passive, though some iridophores can change slowly under chemical control. By opening and closing the chromatophores above these reflectors, the cuttlefish can reveal or hide them, filter their colours, or mix pigment and reflected light. That is how a small set of pigments produces such a variety of colours and effects.

How do cuttlefish change their skin texture?

Colour is only part of the camouflage. Cuttlefish also change the texture of their skin using structures called papillae. These are areas of skin that can be raised into bumps, ridges or tall, branching spikes by muscles in the skin, and flattened again when the muscles relax. Like chromatophores, papillae are under fast nervous control, and a cuttlefish can raise or lower them within a second or two.

Studies by Justine Allen, Roger Hanlon and colleagues have described how the muscles of papillae are arranged and how the animal can hold them raised for long periods without much effort. Papillae allow a cuttlefish to match the three-dimensional texture of weed, coral, rock or algae, breaking up the smooth outline that would otherwise give it away. Combined with postures, such as raised arms that resemble fronds, texture change makes cuttlefish camouflage effective even at close range.

How does a cuttlefish decide which pattern to show?

Mainly by looking. Experiments led by Roger Hanlon, Chuan-Chin Chiao and others placed cuttlefish on artificial backgrounds, such as checkerboards with squares of different sizes and contrasts, and recorded the patterns they chose. The cuttlefish responded to specific visual features: the size of light objects relative to their own white square, the contrast between light and dark areas, the presence of edges, and whether the background was flat or three-dimensional.

From these cues, the cuttlefish selects among three broad camouflage classes, uniform, mottle and disruptive, and adjusts the details. The process does not seem to require the animal to see itself; instead, it uses the information about the background to produce a pattern that a predator’s eye would read as part of the scene. Because cuttlefish appear to be colour-blind, this matching is thought to rely mostly on brightness, contrast and texture rather than on colour itself.

Does the skin help sense light?

Possibly. In 2010, Lydia Mäthger, Steven Roberts and Roger Hanlon reported in Biology Letters that cuttlefish skin contains opsins and other proteins normally found in the eye’s light-sensing cells. Similar findings in octopus skin suggest that cephalopod skin may be able to detect light directly, at least crudely.

What this means for colour change is not yet clear. The skin is unlikely to form images, but it could help the animal sense the overall brightness of light falling on different parts of the body, perhaps fine-tuning colour change locally. The eyes remain the main source of information, and experiments show that cuttlefish deprived of a view of the background cannot camouflage accurately.

What have scientists learned by filming chromatophores?

Recent studies have taken colour-change research to a new level of detail. In 2018, a team led by Sam Reiter and Gilles Laurent at the Max Planck Institute for Brain Research in Frankfurt published a study in Nature in which they filmed cuttlefish skin at high resolution and tracked tens of thousands of individual chromatophores over time. They found that chromatophores work in coordinated groups, and that the patterns could be used to infer the activity of the motor neurons that control them.

They also observed how the skin grows. New chromatophores appear between existing ones as the animal grows, and each starts out yellow and darkens over weeks, becoming orange, red and finally brown or black. This explains how cuttlefish maintain a mix of colours as their skin expands. A follow-up study by the same group, published in 2023, found that when cuttlefish change camouflage, the skin does not follow a single direct path from one pattern to the next. Instead it moves through a series of intermediate patterns, pausing and adjusting, as if the animal were using feedback to refine the match.

Is colour change automatic or voluntary?

It is under active control, but much of it is not deliberate in the way a human decides to raise an arm. Camouflage patterns seem to be produced semi-automatically in response to visual input, much as our pupils respond to light or our posture adjusts when we stand on a moving bus. Signalling patterns, such as courtship displays and threats, appear to be more context-dependent, chosen according to the situation and the receiver.

Learning plays a role, too. Young cuttlefish improve their camouflage with experience, and laboratory studies suggest that the environment in which cuttlefish are raised can influence how well they camouflage later. Colour change also continues during sleep: studies of cuttlefish sleep have recorded active phases with rapid eye movements, arm twitches and flickering colour patterns, which some researchers have compared to REM sleep in mammals and birds.

How long can a cuttlefish hold a pattern?

For a long time. A cuttlefish resting on the bottom can hold a camouflage pattern for hours, with only minor adjustments. Holding the chromatophores open requires the radial muscles to stay contracted, but the energy cost appears to be modest, possibly because the muscles have properties that allow them to maintain tension efficiently. In fact, many cuttlefish patterns involve keeping some chromatophores closed and others open in a stable arrangement.

Some displays, by contrast, are designed to change constantly. The passing cloud display, in which dark bands sweep across the body, requires chromatophores to expand and contract in waves. Courtship and fighting displays can also involve rapid flickering. The ability to switch between stable and dynamic patterns is part of what makes cuttlefish so versatile.

Can dead cuttlefish change colour?

Briefly, yes. For a short time after death, the nerve and muscle tissue in the skin can still respond to stimulation. Fishermen and cooks sometimes see chromatophores flickering on freshly killed cuttlefish or squid, and pouring salty sauce over very fresh squid can make the skin pulse with colour, because sodium in the salt stimulates the nerves and muscles.

These effects are not deliberate colour changes, and they stop once the tissue dies. They do, however, demonstrate that the chromatophore system is driven by nerves and muscles: the same system that produces camouflage in the living animal can be triggered artificially. Scientists studying chromatophores in isolated skin use electrical and chemical stimulation for the same reason.

How does cuttlefish colour change compare with octopus and squid?

Octopuses and squid use the same basic system of nerve-controlled chromatophores, reflective cells and, in octopuses, papillae. Octopuses are especially good at changing texture, and some species, such as the mimic octopus, combine colour and posture to impersonate other animals. Squid often have particularly fast and dynamic colour changes, with flashing signals used in communication within schools.

Cuttlefish stand out for the precision of their camouflage on the sea floor and for the variety of their displays, which researchers have studied in more detail than those of any other cephalopod. The common cuttlefish is one of the best-understood colour-changing animals in the world, and much of what we know about cephalopod colour change comes from it.

Are there limits to what a cuttlefish can do?

Yes. The pigments in the chromatophores come only in yellow-orange, red and brown-black, so a cuttlefish cannot produce a true blue or green pigment; those colours come from reflective cells and cannot be switched as quickly. The size of each chromatophore also sets a limit on resolution: a cuttlefish can make fine speckles, but it cannot reproduce detail smaller than the spacing of its colour cells, just as a screen cannot show detail finer than its pixels.

Other limits come from the animal itself. Camouflage depends on vision, so it fails in darkness or when the eyes are damaged, and senescent cuttlefish with failing eyes often camouflage poorly. Injuries can destroy patches of chromatophores, leaving pale scars. And because the system is muscular, it needs a working nervous system and energy: sick, cold or exhausted animals change colour less readily.

How do cuttlefish use colour change when hunting and courting?

Colour change is not only for hiding. When stalking prey, a cuttlefish may hold a camouflage pattern until the last moment, or use moving displays such as the passing cloud. During courtship, males flash intense patterns and iridescent colours at females and rival males, then switch back to camouflage once the encounter ends. The ability to shift from invisible to conspicuous and back again in seconds is what makes the system so valuable.

Why are scientists and engineers interested?

Because colour change offers a window into the brain. The chromatophores are controlled by motor neurons, so the patterns on the skin are effectively a direct readout of brain activity, visible from outside without any electrodes. That makes cuttlefish a valuable model for studying how brains generate complex behaviour and how they process visual information.

Engineers are interested too. Cuttlefish skin has inspired research into adaptive camouflage materials, flexible displays and soft robots that can change colour and texture. Some researchers have built artificial chromatophores using elastic membranes and electrically activated muscles. None yet comes close to the real thing, which combines speed, resolution and texture in a living, growing skin.