Why Do Mantis Shrimp Have the World's Best Eyes?
Mantis shrimp see the world in a way no other animal can match, with up to sixteen types of photoreceptors to our three. Here's what scientists know about how — and why — that vision evolved.
Human eyes work with three types of color receptors. Dogs get by on two. Even birds, often praised for their sharp color vision, top out at four. Mantis shrimp blow past all of them, packing as many as sixteen different types of photoreceptors into a pair of eyes that move independently and can each judge depth entirely on their own.
An Eye Built Like Nothing Else
Mantis shrimp have compound eyes made up of tens of thousands of tiny visual units called ommatidia, arranged in horizontal bands, according to The Conversation. The middle rows of that arrangement form a specialized strip that scans across a scene, giving each eye the ability to perceive depth entirely on its own, without needing input from the other eye the way human depth perception does.
That specialized band of ommatidia is where the real complexity lives. The first several rows detect both visible and ultraviolet light, with each row tuned to a slightly different part of the UV spectrum, giving mantis shrimp unusually fine-grained UV vision, according to Phys.org. The remaining rows are lined with microscopic, precisely angled hairs that let the animal detect polarized light, including the circularly polarized kind that virtually nothing else on Earth can see.
So Why Sixteen Photoreceptors?
Here’s the twist: despite having far more color receptors than humans, mantis shrimp are actually worse than we are at telling similar colors apart, according to reporting in Discover Magazine. Rather than blending signals from a handful of receptors the way our brains do, researchers believe mantis shrimp process color information more directly within the eye itself, which may let them recognize colors rapidly without needing to compare wavelengths the way our visual system does.
That fast, direct recognition could be a real advantage for an animal that has to react in a fraction of a second — mantis shrimp are also known for a punch that accelerates as fast as a fired bullet, and reacting quickly to prey, rivals, or predators may matter more to them than fine color discrimination.
What Is All That Vision Actually For?
Scientists have a few working theories, but no single confirmed answer. Some parts of a mantis shrimp’s own body reflect circularly polarized light, and researchers suspect this could be used for private communication or mating signals that predators simply can’t detect, since so few other animals can see that kind of light at all, according to Discover Magazine. Other researchers have proposed that the polarization vision helps mantis shrimp navigate cloudy water or spot camouflaged prey that would otherwise blend into the reef.
Male and female mantis shrimp of some species even produce these polarized reflections from different parts of their bodies, hinting that the signals may play a role in courtship, according to National Geographic.
A Visual System Still Not Fully Understood
Despite years of study, researchers still don’t fully know how a mantis shrimp’s relatively small brain manages to process such an enormous stream of visual information. Some evidence suggests that a walnut-shaped cluster of nerve cells inside each eye stalk, called a reniform body, plays a key role in filtering and interpreting the signal before it ever reaches the brain, according to ScienceAlert.
Engineers have taken notice, too. The same qualities that make mantis shrimp vision so unusual — rapid pattern recognition, sensitivity to polarized light — have inspired research into new types of cameras and sensors designed to detect cancerous tissue or improve underwater visibility.
Frequently Asked Questions
Can mantis shrimp see more colors than humans? Not exactly. They have far more types of photoreceptors, but studies suggest they’re actually less able to distinguish between similar shades than humans are. Their advantage seems to be speed and range, not fine color discrimination.
Why is mantis shrimp vision considered the most complex in the animal kingdom? It combines an unusually high number of photoreceptor types, sensitivity to ultraviolet and polarized light, independently moving eyes, and the ability to judge depth with a single eye — a combination not found together in any other known animal.
Mantis shrimp remain one of the animal kingdom’s stranger puzzles: a creature seeing the world through more visual channels than almost anything else alive, in ways scientists are still working to fully decode.
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