Did you know that tuna have a third eye? Or that shrimp can see colours we can’t even imagine? We humans rely so much on our eyesight that it’s hard to imagine there are things it can’t do. At least your eyes can help you read a few strange facts about vision in the animal kingdom.
Though it’s hard to see, many fish, reptiles and amphibians have a third eye called the parietal eye. It’s smaller than the other two and often covered by a layer of skin. It usually appears as a small, grey oval between their other eyes. The parietal eye can’t see the same way other eyes do, but it has a small lens and retina that allows it to detect light and dark. It helps animals keep track of the time of day and regulate their body temperature.
That Creepy Glow
Everyone’s seen that creepy Halloween image of a black cat in the middle of the night, invisible except for its shining green eyes. Why do cats have that unsettling trait and we don’t? Actually, it’s not just cats. Lots of animals can do this, particularly ones that are active at night (nocturnal). This includes horses, cows, dogs and hyenas. These animals have a layer at the back of their eye called the tapetum lucidum. When light shines at them from a bright source, they reflect it back like a mirror. This helps them see in the darkness.
Infrared vision – the ability to see heat – is something we think of superheroes having. Well, snakes have it, too! Pitvipers, as well as some boas and pythons, can all see heat. This actually has nothing to do with their eyes, but it’s still a sort of vision. It takes place in a “pit organ” between the eyes and the mouth, which functions differently in different kinds of snakes. Since many snakes have poor vision, this helps them to find warm-blooded prey. It’s so powerful that it even allows a blind rattlesnake to strike at the vital organs of its prey. Scientists have recently discovered that this pit organ is not just for hunting, it’s also a survival tool. The snakes that have it are better at finding a place to warm themselves up than other snakes who don’t.
Expanding the Rainbow
We have something in our eyes called cones that allow us to see colours. Our eyes have three cones: red, green and blue. By combining them, we see all the colours that we think of in a rainbow. But we’re missing out. Some other animals have far more cones than we do. The mantis shrimp takes the prize, with sixteen cones in their eyes! This means they see colours that we can’t even dream of. Scientists have also speculated that some women have a fourth yellow cone that allows them to see more variations in colour than the rest of us. So maybe you or your sister is privileged with seeing a wider rainbow than the rest of us.
It’s easy to think of us humans as being the most evolved species on the planet. Sometimes we forget that even a cow sees things in a way that we can’t!