What The Oatmeal Might Have Gotten Wrong About Mantis Shrimp

OdontodactylusScyllarusMantis shrimp are amazing little creatures. I was delighted to write about their superfast punch in a story last year. And that punch was one of the highlights in a fabulous online comic published by The Oatmeal yesterday, titled “Why the mantis shrimp is my new favorite animal.” But before getting to the punch, the comic discusses the critter’s vision. Here’s a sampling of what it says (minus the illustrations):

Our eyes contain millions of light sensitive cells, called rods and cones. Rods enable us to see light and motion. Cones enable us to see color….

When it comes to color vision, butterflies are almost the top of the food chain. There is one animal that has better vision than the butterfly: the mantis shrimp.

…this marvelous creature has not two, not three, not five, but sixteen color-receptive cones. The rainbow we [humans] see stems from just three colors, so try to imagine a mantis’ rainbow created from sixteen colors. Where we see a rainbow, the mantis shrimp sees a thermonuclear bomb of light and beauty.

This makes for a very pretty comic, but it may not be quite true, as demonstrated by a color test that was given to one mantis shrimp species, Haptosquilla trispinosa. The test, which was described in Science News last year, was carried out by Hanne Thoen, of the University of Queensland in Brisbane, Australia, who presented her results at a scientific meeting in Maryland:

Thoen tested the color vision of mantis shrimp by training them to scoot out of their burrows toward a pair of optical fibers and punch at the one glowing a particular color. As she narrowed the color gap between the two fibers, she could tell when the animals no longer discerned a difference.

People can distinguish some colors that are only a nanometer or two different. But mantis shrimp “flunked” this color test when the colors were 15 nanometers apart. So on a test like this, human vision might actually be better than that of mantis shrimp.

Researchers are still working out the reasons why the mantis shrimp might not be as discerning as we are when it comes to color, but brainpower might explain it. From Science News:

People and other animals studied so far distinguish colors through brainpower by interpreting competing activity in different kinds of light-receptor cells. Instead of doing such fancy brainwork, mantis shrimp may just rely on what a particular specialized cell responds to strongly. Wavelengths that tickle the purple-sensitive cells may be just plain purple regardless of whether they’re more toward the blue or the ultraviolet.

This was only one simple test of one species, and scientists are still figuring things out, so we can’t say for certain that mantis shrimp don’t have amazing vision. But humans also beat the shrimp in another area of sight, because the invertebrates aren’t great at seeing light in the red range. Those are the first wavelengths absorbed by water, so there’s not much need for cells to detect a color that doesn’t exist in their world. The wavelengths they can detect can vary, however. Scientists have found that mantis shrimp can tune their vision to the environment they grow up in, so those that live in shallow water will see different colors than those from the deep.

One place that the shrimp definitely have us bested in terms of vision, though, is ultraviolet — at those wavelengths, they can see things we never will. Whether that means the mantis shrimp can see a “thermonuclear bomb of light and beauty,” well, it’s hard to tell. But they certainly are beautiful, awesome creatures nonetheless.

Image of a mantis shrimp (Odontodactylus scyllarus) courtesy of Silke Baron, via wikimedia commons