Octopuses have attracted fascination for millennia. Aristotle (384–322 BC) was one of the earliest fans we know about. Among his other accomplishments, Aristotle was a talented biologist and named over five hundred species of birds, mammals, fish, and invertebrates in his History of Animals, written in 350 BC. Most of his invertebrate observations came from his time on Lesbos in the Greek islands on underwater swims in the Pyrrha lagoon (now called the Gulf of Kalloni). It is mind‑bending to read of his fascinations with octopuses and his observations of their denning behavior and how they change their color and form. He must have spent a lot of time watching them 2,500 years ago to observe what they eat, how they hunt, and how they age, as described in History of Animals:

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The octopus…will approach a man’s hand if it be lowered in the water; but it is neat and thrifty in its habits: that is, it lays up stores in its nest, and, after eating up all that is eatable, it ejects the shells and sheaths of crabs and shell‑fish, and the skeletons of little fishes. It seeks its prey by so changing its colour as to render it like the colour of the stones adjacent to it; it does so also when alarmed. By some the sepia [aka cuttlefish] is said to perform the same trick; that is, they say it can change its colour so as to make it resemble the colour of its habitat. The only fish that can do this is the angelfish, that is, it can change its colour like the octopus. As a proof that they do not live into a second year there is the fact that, after the birth of the little octopuses in the late summer or beginning of autumn, it is seldom that a large‑sized octopus is visible.

The biology behind the skin shifts of octopuses has baffled scientists for the thousands of years since Aristotle. It wasn’t until the early 1800s that scientists investigated actual mechanisms behind this astounding ability. At first, scientists hypothesized that octopuses and other cephalopods changed their color through release of liquid pigment; however, it was soon observed that the various colors are housed in small spots in the skin, which change their size and form, but not location. In 1819, Giosuè Sangiovanni was the first to recognize these color‑filled dots as specialized mini‑organs embedded in the skin and responsible for cephalopod skin color change.

As far as humans are concerned, the ability of the octopus to change the color, pattern, and texture of its skin in an instant is otherworldly.

The next question was how chromatophores so rapidly produce different colors and patterns. Early researchers disagreed about the potential role of nerves and muscle fibers in the contraction and expansion of chromatophores. In 1882, French naturalist Raphaël Blanchard suggested that cephalopod chromatophores, while controlled by the nervous system, are made up of connective tissue rather than muscle fibers. He thought that cephalopod chromatophores had the same general structure as those in other animals including fish, frogs, and chameleons. However, other researchers of the time believed the fibers surrounding chromatophores were muscles and controlled by nerves. In 1892, Césaire Phisalix developed the theory of chromatophores being controlled by muscular fibers.

Finally, in 1901, Eugen Steinach proved Phisalix right with experiments showing that the chromatophore organs are controlled by the radial muscle fibers. Eventually, in 1932, Enrico Sereni and John Young showed that the chromatophores were also directly controlled by the brain. In the late 1960s, Ernst Florey and coworkers from the Department of Zoology at the University of Washington established a more complete working model of the chromatophores in squid as an organ with unusual brain connections and comprising five different cell types. Because Florey and Richard Cloney worked with chromatophores of squid at our own Friday Harbor Laboratories, I feel honored to be able to show their diagram of the structure of the cells in a squid chromatophore. The dark area in the center is the ink sac, surrounded by neurons to fire the radial muscles that enlarge the sac and make the skin appear darker.

A squid chromatophore with inner pigment sac and radiating muscle fibers. Redrawn from E. Florey. AM. Zoologist (1969), 9:429–42.

Investigation of the other cell types involved in color change, the leucophores and iridophores, didn’t occur until the mid‑twentieth century and was aided by improved microscopy. These also appear under neural control and can be adjusted and tuned for the desired reflective effect. Remember that iridophores are also the cells that sparkle in the skin of giant clams and change the wavelength of light that reaches the photosynthetic algae cells. In squid, iridophores can be tuned to change the wavelength of light they reflect and change their color. Similarly, some squid have adaptable leucophores that can change from transparent to reflective.

One reason I’ve delved deeply into the mechanisms of skin control in octopuses is that engineers and scientists are applying what we’ve learned about octopus skin to the design of high‑tech smart materials. The smart skin of an octopus is a superpower that has dazzling capabilities. As far as humans are concerned, the ability of the octopus to change the color, pattern, and texture of its skin in an instant is otherworldly. We know a lot about how the shift is worked in the skin itself, but the way it is initiated by the brain and how the central brain interacts with the other eight brains in the arms remains unclear. Knowing how it’s done doesn’t actually demystify the wonder, because there is still more mystery than known science about how the magic is worked, especially from the perspective of a human who cannot do any of this.

A tricky part of reinventing the camouflage of an octopus for human application is its biological complexity. Both skin texture and color change are under electrical control by the nervous system, making them inspiration for smart materials. Smart materials are a big thing these days; they are those whose properties can be changed by external controls like temperature or humidity or electrical charges. Imagine a soldier’s camouflage jacket that can change to match its background at the flip of a switch. Researchers from the University of Bristol have designed an artificial material that mimics just the color change by octopus chromatophores. An artificial skin made from stretchable material can effectively and instantly mimic the shade and color changes of chromatophores because it’s under electrical control. At the flip of a switch that sends a charge of electricity, this material can change color and shade, and bands of color waves pass across the material, like the “passing cloud” display of an octopus.

Mimicking texture change in artificial materials is even more complex than color change. Engineers have studied how octopus skin can shift from smooth to bumpy in a split second. Recall that the papillae in octopus skin can change shape with muscle contractions under neural control. James Pikul, an engineer first at Cornell University and then at the University of Pennsylvania, studied the shape changes in the papillae of Octopus rubescens, a small California octopus. It has numerous skin papillae for camouflage and can extend a conical papilla 4 millimeters high in 220 milliseconds after activation, literally in the time it takes to blink an eye (200 milliseconds). He and his students produced a synthetic mimic of these texture changes.

Pikul and his team combined a stretchy silicone layer with an inflexible fiber mesh in predetermined shapes that could be inflated like a balloon to a 3D form. This work was initially funded by the US Army, which, not surprisingly, is interested in better ways to camouflage soldiers and tanks. The work is a leading venture in the science of smart materials and is now funded by prestigious basic research agencies. Their work with smart materials and surface texture also intergrades into programmable stiffness that can be controlled electrically. The key attribute of octopus smart skin is that it is under neural control, which is essentially electrical control, and triggers change in the blink of an eye. The skin of sea stars is also of interest in designing smart materials because of its strange properties under neural control, so I’ll continue the discussion of engineering applications of programmable smart materials in chapter 8. These are both fantastic examples of the value of bio-inspired design and the transformative advances in useful applications derived from the otherworldly innovations of invertebrates.

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All cephalopods, from octopuses to squid to cuttlefish, seem alien for their slippery shape‑shifting, smart skin, and uncanny intelligence. Adding to the strangeness of their alien ways, many of the cephalopods are creatures of the night sea, and so it was on night dives that we went to find them. I was enticed into night dives in Hawaii and Indonesia between 2010 and 2016 with videographer David O. Brown to find and film living matches to Blaschka glass models of invertebrates. In the next chapter, I describe how the Blaschkas chose some of the most enchanting animals in the sea as subjects, from the ethereal jellyfish to bright‑spotted nudibranchs to shape‑shifting cephalopods. While the Blaschka glass collection includes multiple species of octopuses, squid, and cuttlefish, the array of octopus species is dazzling in showing more shapes, sizes, and capabilities than I have ever seen in life, from tiny to large.

Now when I see an octopus or cuttlefish, I don’t see just the animal but also their quest for a good life.

The most memorable night dive with David was to a small coral reef near shore on the Big Island of Hawaii. When we first met, David’s expertise was filming huge fantastic things like beluga and humpback whales with the Philippe Cousteau crew. But he has an eye for any kind of natural wonder and has long loved all kinds of cephalopods, from squid to cuttlefish to octopuses, so he had more skills than I in finding them on night dives. I didn’t quite believe his calm certainty that if we did night dives in Hawaii we would see octopuses out patrolling. I was busy teaching a field course to Cornell students and was a bit grudging about freeing up my schedule from nighttime lecture writing to go on dives, but I was willing to give it a try. We went with Denise Vidosh and Dave Rafalovich, owners of my favorite dive company, Blue Wilderness Dive Adventures.

The four of us plus a boat captain headed out in the dark and soon reached a nearby site where Dave had seen octopuses. We dropped into the water with our lights and started poking slowly around the edge of the night reef. I was busy watching a bright pink flatworm crawl into a crevice when I heard the demanding, rapid tank clang. We can’t yell to our partners underwater on a dive, so when we want to get everyone’s attention, we bang on our tanks with dive knives, and the sound carries well underwater. This was an urgent, “come quickly” clang, either a cool find or a dangerous threat. I held my breath to listen and localize the sound and then swam fast go see. Dave and Denise had corralled a gorgeous spotted octopus (Callistoctopus ornatus), and David gestured for me to go close while he filmed it. I slowly moved in, amazed by the find.

This was different from the wily, muscular day octopus I was to struggle with on a reef a few days later. This was a quiet, calm, serene creature. I moved in and easily picked it up. It perched calmly in my hand, and we eyed each other. Its eyes were large and luminous and met my own. It felt like being eye to eye with a human, except eerily different, because the shape of an octopus iris is more rectangular than round. I was completely lost in its gaze.

When I held that octopus and it sat calmly in my hands, a bond grew. I fell in love. I truly loved this animal and its epic quest to survive in our oceans. In that moment of love and empathy, I imagined I understood all it took to be an octopus: the challenge of creeping through the night reef to find prey like small crabs, the dangers of predators and the need to be on constant watch, the patience and obsession of caring for the eventual brood of eggs and tiny octopus hatchlings.

Now when I see an octopus or cuttlefish, I don’t see just the animal but also their quest for a good life, and I want that for them in the same way most people want a good life for their children. They are real beings to me. It was a reminder that in addition to a global ecologist dealing with climate change and human impacts to once pristine oceans, I am also an invertebrate naturalist. These animals themselves are the source of my passion for sustaining our oceans. My bond with creatures in the ocean reverted to being heart‑driven from being data‑driven.

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From The Ocean’s Menagerie: How Earth’s Strangest Creatures Reshape the Rules of Life by Drew Harvell. Published by Viking, an imprint of Penguin Publishing Group, a division of Penguin Random House LLC. Copyright © 2025 by Drew Harvell.