These are the weird and wonderful reasons octopuses change shape and color

Almost all cephalopods—the class of ocean dwellers that includes octopuses, cuttlefish, and squids—have an incredible ability not just to change the color and patterns on their skin, but also to transform their body’s shape and texture.

Thanks to these tricks, cephalopods can radically change their appearance faster than the blink of an eye, the swiftest known change in the animal kingdom.

“They're the best at it of anything that we know,” says Michael Vecchione, the curator of Cephalopoda at the Smithsonian National Museum of Natural History. This is especially surprising since most cephalopods are color-blind, so we have yet to understand how they can fully perceive what to copy in the first place.

“It has to have been evolutionarily important for them to evolve [the ability to change color and texture] and to evolve so many different versions of it,” says Vecchione. Indeed, studies suggest that each cephalopod species has evolved up to 30 different ranges of patterns to hide in plain sight.

This group of soft-bodied mollusks have skin covered in millions of pixel-like cells called chromatophores: pigment-filled sacs each surrounded by their own small muscle fiber. These muscles can stretch the chromatophore to flood with color or contract and shrink to a dot, creating varied, complex patterns. Octopuses and cuttlefish are also covered in small bumps, flaps, branches, and ridges called papillae, which can be ruffled upwards or smoothed out to create different skin textures too.

(Stream Secrets of the Octopuses now on Disney+ and Hulu)

The common day octopus (Octopus cyanea) can become almost see-through beige and white on flat sandy surfaces; dark, mottled, and rugged on bumpy rocks; and flashes orange, red, and brown spikes along corals. Cuttlefish sometimes clump up, shrivel, and hide their arms to look like a tuft of algae, and baby giant cuttlefish (Sepia apama) hiding among seaweeds have been recorded sending waves of shaded dark brownish-green pigments across their body to copy the motion of swaying seaweed.

While these shapeshifting skills certainly come in handy for inconspicuous disguises, there are many other reasons octopuses and other cephalopods change their skin—and they may surprise you.

To intimidate predators

Sometimes cephalopods need to do the opposite of blending in to escape a predator.

If they’ve been caught while in camouflage, many octopus species can turn their bodies dark and cloudy, darken their eyes, stretch out their body and arms to look bigger and stand taller. Cuttlefish even create eye-like shapes on their mantle — their sack-shaped body — back to stare down their predator.

Predators learn to associate the highly venomous blue-ringed octopuses with the gaudy rings of indigo they flash across their yellow skin to alert predators they’re not to be messed with.

(8 fascinating facts about octopuses—from their supersmarts to their favorite foods.)

Meanwhile, the less-dangerous mimic octopuses (Thaumoctopus mimicus) impersonate all sorts of animals that are more threatening or venomous than they are. Among many other disguises, they can spread out their arms and display white and brown stripes to look like the sharp-spined, highly venomous lionfish.

To trick and hypnotize their prey

Mimicking other animals also helps cephalopods to appear less threatening and get close to their prey. Pharaoh cuttlefish (Sepia pharaonis) have been seen using their color, texture, and movement to appear as docile hermit crabs to their prey, the tropical damselfish. Caribbean reef squid (Sepioteuthis sepioide) swim in reverse and wave their arms like fins to look like herbivorous parrotfish, also to get close to their prey.

Cephalopods can also send stripes, circles, and patterns of color across their body as if to bamboozle their prey before striking. Martin How, an ecology of vision researcher at the University of Bristol, studies how Broadclub cuttlefish (Sepia latimanus) ripple dramatic dark rings of color from their head to their arms as they get closer to their prey. “It’s almost like a magician trying to mesmerize, or hypnotize their audience,” he says, theorizing this helps the cuttlefish is disguise its approach, looking farther than it is, to catch the prey off guard.

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The tropical octopus (Octopus laqueus) has also been spotted pulsing dark patterns to make an inverse illusion—appearing to be moving forward while it remains still, tricking the prey into moving out of a hiding spot, according to How. This has been reported in other species of octopuses too.

“For decades we've been studying camouflage as a static thing,” says How. “But actually, once you actually can make a moving pattern on your body, you can do all kinds of really interesting things.”

To communicate between themselves 

Social Humbolt squids (Dosidicus gigas) found a way to communicate by appearance even in the depths of the ocean where there’s little sunlight. They make their own light with cells called photophores to create a luminous backdrop against which to display their color changes—like an e-reader. They likely use these signals to help organize swimming in schools during their daily vertical migration between deeper and shallower waters, according to Vecchione.

(These creatures of the 'twilight zone' are vital to our oceans.)

These male jumbo squids also use skin signals to fend off other males, demonstrating dominance by flashing dark darts of colors across their bodies. Similarly, when cuttlefish males encounter other males they splash zebra patterns of black and white stripes while flapping their fins.

“Some of the most amazing signaling they do [is] between each other,” How says of the cuttlefish.

To snatch the perfect mate

When communicating within their species, who could be more important than a potential mate? To impress ladies, male day octopuses (Octopus Cyanea) will turn pale and flash black stripes down their bodies, while male Caribbean reef squids (Sepioteuthis sepioidea) turn a rich, dark red.

Since small male Australian giant cuttlefish don’t stand a chance in competing for a female when a larger male is around, they need to sneak around. They change their color and posture to impersonate females, get close to other females, then mate with them right under the larger male’s nose. Some species of cuttlefish can literally split their mantle in half and show both patterns at once: a courtship pattern for the female, and a deceptive pattern for their rival.

Can cephalopods show their thoughts on their skin?

Though scientists have observed many interesting examples of color, shape, and texture changing seemingly to achieve a goal, research cannot yet point to any intentionality behind these signals—like whether octopuses are consciously mimicking more threatening sea creatures.

(An octopus invited this writer into her tank—and her secret world.)

“It doesn't mean that the octopus itself is aware of what it's doing,” says Tessa Montague, a cephalopod neuroscientist at Columbia University. She says it’s probably a case of natural selection: one of these animals might have started behaving this way, and they didn't get eaten.

Montague’s approach to studying cephalopods is using the color and pattern changes in their skin to parse what’s going on in their minds. For instance, when cephalopods display their threat patterns as they run away from predators, those are probably involuntary reactions to their brain activity, she says. Their skins are likely reflecting their fear, stress, aggression, or desire to mate.

That’s why footage of an octopus flickering different colors during its sleep has been used to study whether cephalopods dream during their slumber.

“We argue that perhaps that is actually a physical manifestation of an internal state,” says Montague. “They have this incredible electric skin that is basically showing you what they're thinking.”