How do squids camouflage themselves?

How do squids change color?

Many species of octopus are distinguished by their special intelligence: The animals can open screw-top jars, use tools and even count. They may also have clairvoyant skills - at least when it comes to soccer games. But one of its most amazing properties is the ability to make yourself almost invisible in a flash. The perfect optical adaptation of the cephalopods to their environment is based on the unique structure of their skin. This consists of three different layers, whereby individual skin cells are directly connected to muscles and nerves.

The upper layer of the skin of the squid contains cells with an elastic outer shell and different colored pigments. These so-called chromatophores are in direct contact with muscle fibers, which can relax and contract. When the muscles are relaxed, the cells can expand and the color becomes visible on the outside. If the muscles are tense, they are compressed and the color can no longer be seen from the outside.

Under the chromatophores there are two further cell layers that have an influence on the coloring: First there are cells that act like special filters. They amplify or swallow a portion of the light that is reflected by the colored chromatophores - depending on the angle from which you look at them. At the very bottom, the octopuses have a layer of white skin cells, which, like a canvas, provides a high-contrast background.

But how do the squids even know what the subsurface looks like, the look of which they are imitating? The animals not only use their eyes for this, but also their skin, which reacts to differences in brightness. This is because it contains rhodopsins, the same type of light-sensitive proteins found in the eyes. On the other hand, the animals can only perceive shapes or contrasts with their eyes, and they can do so with astonishing precision: If they are at the transition between two different-looking surfaces, they can adapt one side of the body to one and the other side of the body to the other. Even artificial patterns that cannot be found in nature do not cause them any problems.

In addition to the color appearance, the animals also imitate the surface structure. To do this, they change their skin surface, which can appear either smooth or wart-like. To make its camouflage perfect, the so-called mimic octopus also imitates the shape of other animals, such as those of a sea snake, a flounder or a lionfish.

Squids use their changeability not only for camouflage, but also as a means of communication. Usually they are loners. However, as soon as they meet a conspecific, they send different signals through color changes. In turf wars, they take on the darkest possible color - usually the one who wins the duel is who is almost black. If a male feels directly inferior, it can also happen that it simply disguises itself as a female by taking on an inconspicuous spotted coloration. But even when a male meets a female, a lively color change can be observed, and in around ten percent of cases this animal flirtation ends with a mating attempt.