Slurp!

Here’s a challenge: Stick out your tongue and try to lick your nose. Could you do it? If so, congratulations. You’re one of the 10 percent of humans who can. Now stretch your tongue farther and try to lick your eyeball. Could you do that? Surely not.

Unless you are a gecko.

Geckos are small lizards found in warm climates around the world. And most species of geckos lick their eyes many times a day. This is not because their eyeballs taste delicious. (Though maybe they do—who’s to say?) It’s because these geckos lack something that humans and many other animals have: eyelids.

Your eyelids—the thin pieces of movable skin above and below your eyes—are there to protect your eyes. If a light is too bright or if something comes too close to your delicate eyeballs, your trusty eyelids snap shut. They close to keep your eyes safe.

Another way your eyelids protect your eyes is by cleaning them. Each time you blink, your eyelids wipe away sweat, dust, and other tiny bits of muck. Eyelids also spread moisturizing tears across your eyeballs. These tears contain a special substance. That substance is called lysozyme. Lysozyme helps prevent infection. 

Instead of eyelids, most geckos have transparent coverings called spectacles over their eyes to protect them. These spectacles are like windows—windows that don’t open or close.

Without an eyelid to clean it, a gecko’s spectacle collects grime from the surrounding environment. When the spectacle accumulates too much grime, the gecko’s long, sticky tongue comes to the rescue. It flicks out of the gecko’s mouth and, with a little squelch, coats the gecko’s eye with saliva and slurps the grime away.

Now, you might be thinking that geckos have a weird way of cleaning their eyeballs. But perhaps geckos are thinking the same thing about us!

This article was originally published in the September 2020 issue.