We've all heard about octopi that can change color to mimic their environment. But how do they do it? I discovered the answer when writing The Big Green Book of the Big Blue Sea for Kids Can Press.
The book is designed to present information to kids ages 8-12, but also to engage them with cool hands-on (or do we call that "experiential" now?) activities. Most people learn best by doing, and doing stuff that involves splashing water is pretty well a can't-fail learning opportunity.
Coming up with ideas is pretty easy for me. But coming up with ideas that any klutz, I mean kid, can do (And I am the klutz in question; if I can't do it successfully, it won't go in the book) wasn't a piece of cake. Luckily, cake was not required. Waxed paper and food coloring, however, were.
3. Staying away from the edges of the waxed paper, carefully place 10–20 drops of food coloring on the waxed paper about 1 cm (½ in.) apart. Can you still see the gray newspaper between the colored dots?
4. Hold the second sheet of waxed paper above the first sheet. Gently place it on top of the first sheet. See how the spots seem to spread out? Gently press on them with your thumb to spread them out even more. Can you still see the gray newspaper? Or does your octopus skin look yellow?
5. Lift the top sheet of waxed paper off the bottom sheet. Do the dots return to their original size?
What’s Going On?
An octopus can change color to hide from prey or predators by blending into its surroundings. Many scientists think octopus also use color to communicate and express emotions, such as fear or dominance.
But how do our wriggly friends achieve this tint-o-riffic trick? Octopus skin contains microscopic pigment-filled structures called chromatophores, represented here by the dots of food coloring. Real chromatophores are so small, you can’t usually see them.
When an octopus wants to change its hue, it changes the size and shape of its chromatophores. Your thumb, forcing the dots to expand, acts like the small muscles in the octopus’s skin. They pull on the chromatophores to widen them. Now the skin they’re in is filled with color!
When the octopus relaxes, the chromatophores shrink back to their normal size. The octopus’s skin returns to its original color.*
*Excerpted from The Big Green Book of the Big Blue Sea, Copyright 2011 by Helaine Becker, Kids Can Press, Publisher. All rights reserved.