An octopus can change the color of its skin to blend in with its surroundings. The skin cells behind the trick are called chromatophores. They are special pigment cells that let an octopus change color. Tiny muscles around each color sac squeeze it open or let it close, so the color shows more or less. All of this can happen very fast, because octopuses can change color faster than almost any other animal.

People have been watching this trick for a long time. About 2,400 years ago, the Greek philosopher Aristotle wrote detailed notes on how octopuses camouflage themselves. Much later, fishermen in Indonesia first detected the mimic octopus in 1998. The mimic octopus can copy the look and moves of several different animals. Some of what we know about octopus disguises is very old, and some of it is quite new.

The skin does more than change color. Iridophores are skin cells that make shiny, rainbow-like colors, and an octopus can also change the texture of its skin by raising bumps called papillae. Some colors are meant to be seen. A blue-ringed octopus is a small octopus with bright blue rings. It flashes the blue rings as a warning, and people should never touch one.

Still, not every octopus fits this picture. Not every octopus species can change color, and the way they do it can differ. Glass octopuses have lost all their chromatophores and are almost completely see-through. For a glass octopus, the cells that let most octopuses change color are gone. The famous color trick belongs to many octopuses, but not to all of them.

Words to know

• chromatophores: color cells
• camouflage: hide by blending
• iridophores: shiny cells
• papillae: skin bumps
• mimic: copycat