Who's lookin' at you???? - facts about the eyes of different animals

Ranger Rick, August, 1997 by Ellen Lambeth

Eyes are an animal's windows to the outside world. But all eyes are not the same. Bet you recognize the eye in photo 1. Now try to spy the eyes of a frog, fish, bird, sheep, insect, snake, cuttlefish, two lizards, and two shellfish on these next pages. Then check your guesses on pages 8 and 9.

Here's Who's Lookin' at You

1 Human Your eye has lots of protection. A lid blinks over it. Lashes keep stuff out of it. And tears keep it moist and clean. The colored part, called the iris, can open and close to make the black hole in the middle--the pupil--bigger or smaller. The wider the pupil is, the more light enters the eye. Light is what makes vision possible.

2&3 Shellfish That's not a three-eyed monster in photo 2. In fact, this thorny oyster has dozens of eyes, but they don't see all that well. They mostly make out the difference between light and dark. So a shadow passing across the eyes can mean a predator moving in for the kill. That's when the shell shuts and the oyster scoots off. The queen conch (3) stays in its shell while sticking out its two long eye stalks. What a great "eye-dea"--periscope eyes!The animal can wave them around underwater to see what's going on. If danger appears, the conch can pull the eyes safely into its shell along with the rest of its body. If the coast is clear, it can come back out.

4 Lizard The Tokay gecko is active at night. The pupil of the gecko's eye is a slit that opens wide to let in as much night light as possible. When there's too much light, the pupil can close up to the size of four tiny pinholes. This blocks out more light than any other kind of eye can while still letting the eye focus.

5 Frog Like most frogs, the horned frog has round, bulging eyeballs. They help it see almost all the way around itself without moving its head. This frog gets its name from the flap of flesh sticking up above the eye. This "horn" may help protect the eye like an eyebrow. Or it may help make the frog look too big to eat. (No one knows for sure.) See the dark lines on either side of the pupil? They blend into the skin pattern next to the eye to form a mask. This mask helps disguise the eyes from enemies.

6 Sheep Most hooved mammals, such as this bighorn sheep, have large eyes and good vision. The sheep uses different parts of its eye to focus on things that are close up and things that are far away.

7 Insect Each of our eyes has a single lens. This lens focuses light to form a picture of what we see. But each huge eye of a horsefly (and many other insects) is made up of hundreds of lenses. Each little lens picks up a slightly different view. And all the views together form one big picture. This type of eye is called a compound eye. It helps the fly see in all directions at once. And that's great for seeing anything move anywhere nearby.

8 Bird You can tell this one's a bird because of the feathers around the eye. Birds, such as this great horned owl, have some of the biggest eyes for their body size. And see that clear shade pulled across the eye? That's a third eyelid. All birds have it to help clean and protect the eye. The owl can use it to avoid injury as it flies through the forest after prey.

9 Snake Scaly skin is a good clue that this eye belongs to a reptile. But "no eyelid" is the clue that clinches it as belonging to a snake. This one is an emerald tree boa. Snakes don't need lids because they never have to close their eyes. Each eye is covered by a clear scale, which protects it. When the snake sheds, the outer layer of these scales pops off right along with the rest of the skin. This snake's vertical (up-and-down) pupil is great for opening up extra wide at night to let in as much light as possible.

10 Lizard This eye is ringed by scaly skin too . . . and also by an upper and lower eyelid. So it's pretty clear that the eye belongs to a reptile, but not to a snake. It's actually the eye of a large lizard called a common iguana.

11 Fish You won't see any blinking here. This eye belongs to a parrotfish, and fish can't close their eyes, even when they're sleeping. The watercolor look of the fish's body is in its eye too. That helps make the eye--and head--of the fish a little less noticeable to predators.

12 Cuttlefish Like its octopus and squid relatives, the cuttlefish has excellent eyesight. When the cuttlefish is in deep, dark water, the horizontal pupil in its eye usually opens wide to let in more light. But when the animal is in shallow, bright water, the eye squeezes into the squinty, ripply slit shown here.

By the way, here's the creature whose eye stared at you from pages 2-3. It's a crocodilefish, and it blends in like a crusty rock on the ocean floor. The fleshy, seaweed-looking fringes help disguise the eyes.--Ellen Lambeth