Can Mantis Shrimp See More Colors Than Humans? Myth Checked

Where the “more colors” claim comes from

The claim starts with a real and remarkable fact. Humans have three types of cone cells for color vision, sensitive to blue, green and red light, plus rods for seeing in dim light. Mantis shrimp such as the peacock mantis shrimp have 12 types of photoreceptors for color, and several more for polarized light, up to about 16 types in total.

From this, viral posts and comics concluded that mantis shrimp must see thousands or millions more colors than we do, a world of colors we cannot imagine. It seemed logical: if three receptor types give us millions of shades, surely 12 would give far more.

Scientists were not sure, because more receptor types only produce finer color vision if the brain compares their signals in the right way. In 2014, they put it to the test.

How mantis shrimp eyes are built

Each mantis shrimp eye sits on a mobile stalk and moves independently, so one eye can look forward while the other looks to the side. The eyes can tilt and rotate widely and track moving objects with quick, jerky movements.

Each eye is a compound eye made of tens of thousands of small units called ommatidia, divided into three parts: an upper half, a lower half and a narrow middle band. In the peacock mantis shrimp and its close relatives, the middle band has six rows of specialized units.

• Rows 1 to 4 handle color. They contain 12 types of photoreceptors, several of them tuned to ultraviolet light, and built-in colored filters that sharpen what each receptor responds to.
• Rows 5 and 6 handle polarized light, the direction in which light waves vibrate.
• The upper and lower halves handle shape and movement, like the eyes of many other crustaceans.

Because the three regions of one eye can look at the same object, a mantis shrimp can judge distance with a single eye. The middle band only covers a thin strip of the view at any moment, so the animal sweeps it across a scene, scanning like a barcode reader.

What the 2014 color test found

In a study published in the journal Science in 2014, Hanne Thoen, Justin Marshall and colleagues at the University of Queensland trained mantis shrimp to pick a particular color to get a food reward. They then offered choices between the trained color and others that were closer and closer in wavelength, to find out how small a difference the animals could detect.

The result surprised many people. The mantis shrimp could only reliably tell colors apart when they differed by about 12–25 nanometers in wavelength. Humans, by comparison, can distinguish differences of about 1–4 nanometers in parts of the spectrum. In other words, the shrimp were much worse at fine color discrimination than we are.

The researchers suggested that mantis shrimp use a different system. Instead of comparing the signals of different receptors in the brain to work out subtle shades, as we do, they may recognize colors directly by which receptors fire, almost like reading a barcode. That would let a mantis shrimp identify a color very quickly with little brain processing, which matters for an animal that hunts and fights at high speed. A later study in 2022 found that at least one species can still distinguish strong colors from pale ones, so the brain likely does some comparing too, and the full picture is still being worked out.

Ultraviolet: colors we cannot see

Where mantis shrimp truly beat us is range. Their eyes respond from deep ultraviolet light, around 300 nanometers, to far red, around 720 nanometers. Human eyes see roughly 400 to 700 nanometers, and the lens of our eye blocks most ultraviolet light.

So mantis shrimp can see patterns that are invisible to us. Many reef animals have ultraviolet markings, and some prey that is nearly transparent to us may stand out in ultraviolet. Mantis shrimp also have fluorescent and colored body markings, which they display to each other during courtship and contests.

Polarized light: a secret channel

Light travels as waves, and in polarized light those waves vibrate in one main direction or rotate in a fixed pattern. Sunlight reflected from water, and light scattered by the sky, is partly polarized. Many insects, octopuses and cuttlefish can detect linear polarization, but mantis shrimp go further.

Mantis shrimp are the only animals known to see circularly polarized light, in which the light wave rotates like a corkscrew. Some species have body parts that reflect polarized light, which may act as private signals that predators cannot see. The tiny structures in their eyes that convert circular to linear polarization work so well across the spectrum that engineers have studied them as models for new optical devices and cameras.

Humans can barely sense polarization at all. Some people can see a faint yellowish shape called Haidinger’s brush when looking at a polarized blue sky, but our eyes do not use it.

So, do mantis shrimp see more colors?

The fairest answer is: they see differently, not simply more. Mantis shrimp see a wider range of light than we do, including ultraviolet and polarized light, so they can detect patterns and signals completely hidden from us. But within the range we share, humans tell similar shades apart much better.

Their eyes are best understood as fast recognition tools, built for an animal that needs to identify prey, rivals and mates in an instant, and then strike at extraordinary speed, as described in How hard does a mantis shrimp punch?. For another small animal with remarkable vision, see How well can jumping spiders see?.