What Is the Purpose of Squid Ink?

Squid use ink to protect themselves and their eggs from predators. All squid--more than 300 separate species--and most of their relatives, the octopods and cuttlefishes, have the ability to make and use ink. Squid protect themselves with ink in several different ways, depending on the type of predator threatening them.

  1. The Smokescreen

    • The smokescreen is the squid's most well-known way of using ink. Squid spend most of their time swimming in open water, vulnerable to predators. The squid has two organs, a siphon and an ink sac, that open into the mantle, the outer covering of the squid's body. When a predator, such as a fast-moving fish, approaches a squid, the ink sac fills the squid's mantle with ink. The squid shoots the ink at the predator and uses the siphon to suck water into its body, then shoots the water out in a powerful jet. The ink forms a cloud that hangs in the water and obscures the predator's vision. The jet of water spreads the ink around, making the cloud bigger, and quickly propels the squid to another location.

    Chemical Weapon

    • Some predators find squid to prey upon by using chemical sensing organs, rather than eyesight. To evade these predators, a smokescreen is not effective. To escape them, the squid uses special chemicals in the ink that desensitize the predators' chemo-receptors.

    Pseudomorphs

    • To escape larger predators that swallow squid whole, the squid makes bait that shoot out with the ink. These lures are called pseudomorphs. They are colored globs of mucus that float toward the predator. The squid uses the ink to make the pseudomorphs a normal squid color, and then lightens its own body using its natural camouflage. The predator snaps up the squid-colored, squid-shaped bait, and the squid escapes. Young predators who have been tricked into eating pseudomorphs are also less likely to attack the species of squid that made them in the future.

    Protecting Eggs

    • Squid can use ink to protect their eggs. They shoot the ink at tiny, egg-eating predators, such as crabs and snails. Sometimes the ink drives these crawling creatures away, either by annoying and frightening them, or by blocking their sensory organs. Some species also use ink to camouflage their eggs' shells.

    Ink Ingredients

    • The main ingredient of squid ink is melanin, the same pigment that colors mammal hair and skin. Like hair and skin, ink comes in a range of colors from tan to blue-black. Squid ink also contains mucus, which makes the ink thicker and forms pseudomorphs. The chemicals that jam predators' chemoreceptors are neurotransmitters, and include dopamine and several amino acids.