Extraordinary Eyes

What if you could see in the dark? Or focus one eye on your teacher while the other reads a book? For some animals, tricks like these are part of everyday life.

Animals use sight to hunt prey, avoid predators, and communicate. Their eyes work in the same basic way as human eyes do. Special cells in the eye collect light from the environment (see How the Human Eye Sees). These cells send signals to the brain, which creates the images we see.

The structure of an animal’s eyes affects how it views the world. Read on to meet four animals with unique adaptations for vision. Their eyes let them see things no human ever could.

What if you could see in the dark? Or use one eye to look at your teacher while the other reads a book? Tricks like these are part of everyday life for some animals.

Animals use sight to hunt. They use it to avoid being eaten. And they use it to interact with one another. Their eyes work in the same basic way as human eyes do. Special cellsin the eye collect light from the world around them (see How the Human Eye Sees). These cells send signals to the brain. It creates the images we see.

The structure of an animal’s eyes affects how it views the world. Read on to meet four animals with special vision adaptations. Their eyes let them see things no human ever could.

Human eyes are built to see in daytime. It’s not easy to make out our surroundings after dark. Owls, which hunt at night, don’t have this problem. Their eyes are adapted to soak up as much light as possible. This gives them vision clear enough to spot prey even in the dim light of the moon and stars.

How do owl eyes absorb so much light? One reason has to do with the size of their pupils. Owls’ eyes are enormous—much larger relative to their body size than those of many other animals. When it’s dark out, owls’ pupils expand to cover nearly the entire front of their eyes. Those extra-large openings let in a lot of light. Where a human sees a dark forest, an owl sees a scene that’s nearly three times as bright!

Human eyes are built to see in daytime. It’s not easy to make out things around us after dark. Owls don’t have this problem. They hunt at night. Their eyes are made to soak up as much light as possible. That gives them great eyesight. They can even spot prey in the dim light of the moon and stars.

How do owl eyes take in so much light? One reason is that their eyes are huge. They’re much larger for their body size than those of many other animals. Because their eyes are large, their pupils are too. Owls’ pupils expand when it’s dark out. They widen to cover nearly the whole front of their eyes. Those huge openings let in a lot of light. A human might see a dark forest. But an owl sees a scene nearly three times as bright!

A chameleon in the rainforest has a lot to keep an eye on. It needs to watch out for snakes while hunting its own prey—insects. To help, it has eyes that rotate in all directions. This allows the reptile to see around its body without moving its head.

Unlike humans, chameleons can move each eyeball independently. A chameleon might point one eye at a branch above it while the other scans the scene off to one side.

But when a chameleon spots an insect, it swivels both eyes forward. That gives it binocular (bye-NAH-kyoo-lahr) vision. Each eye sees a different, but overlapping, view. The brain combines the two images into one 3-D picture, allowing it to judge how far its prey is. In a flash, the chameleon shoots its tongue at the insect. SPLAT! Dinner is served. 

A chameleon in the rainforest has a lot to keep an eye on. It needs to watch out for snakes. It has to hunt insects at the same time. It has eyes that turn in all directions to help. They allow the animal to see all around its body. And it doesn’t even have to moveits head.

Unlike humans, chameleons can move each eyeball separately. A chameleon might point one eye at a branch above it. The other eye might scan the scene off to one side.

But a chameleon swings both eyes forward when it spots an insect. That gives it binocular (bye-NAH-kyoo-lahr) vision. Each eye sees a different, but overlapping, view. The brain puts the two images together into one 3-D picture. It helps a chameleon judge how far its prey is. The chameleon shoots its tongue at the insect in a flash. SPLAT! Dinner is served.

You may not notice dragonflies when you’re by a lake or pond. But the flying insects definitely notice you. Their giant eyes wrap all the way around their heads, giving them a nearly complete view of their surroundings.

Dragonflies have the largest compound eyes of any insect, with almost 30,000 individual light-sensing parts. Some of the parts even face backward. “A dragonfly can see you when it’s coming,” says Robert Olberg, a dragonfly expert at Union College in Schenectady, New York. “And it can still see you when it’s flying away.”

Olberg has found that dragonflies’ huge eyes make them extremely efficient hunters. When a dragonfly takes off after a mosquito or other prey, it catches it 97 percent of the time!

You may not notice dragonflies when you’re by a pond or lake. But the flying insects definitely notice you. Their big eyes wrap all the way around their heads. That gives them a nearly total view of things around them.

Dragonflies have the largest compound eyes of any insect. Each eye has almost 30,000 light-sensing parts. Some of the parts even face backward. “A dragonfly can see when it’s coming,” says Robert Olberg. “And it can see you when it’s flying away." Olberg is a dragonfly expert. He works at Union College in Schenectady, New York.  

Olberg has found that dragonflies’ huge eyes make them great hunters. Dragonflies hunt mosquito or other insects. And they catch them 97 percent of the time!

With bright-blue heads and multicolored bodies, peacock mantis shrimp are a sight to behold. And they have a talent to match their appearance: Their eyes see colors that human eyes can’t detect!

Human eyes have three kinds of color-sensing cells: one for red light, one for blue, and one for green. Our brains combine these colors into many different shades. Mantis shrimp eyes are different. Instead of three cell types for sensing color, they have 12! That allows them to see colors that humans can’t perceive, says Ilse Daly. She studies mantis shrimp at the University of Bristol in England. 

Scientists don’t know why mantis shrimp can detect so many colors, or how exactly the world appears to them. “It’s very different from how we see it, that’s for sure,” says Daly.

Peacock mantis shrimp have brightly colored bodies. They’re a sight to behold. And they have a talent to match their looks. Their eyes see colors that human eyes can’t!

Human eyes have three kinds of color-sensing cells. One type is for red light. One type is for blue. And one type is for green. Our brains mix these colors into many different shades. Mantis shrimp eyes are different. They have 12 cell types for sensing color, instead of three! That allows them to see colors humans can’t sense, says Ilse Daly. She studies mantis shrimp. She works at the University of Bristol in England.

Scientists don’t know why mantis shrimp can see so many colors. And they don’t knowhow exactly the world looks to them. “It’s very different from how we see it, that’s for sure,” says Daly.