Every now and again, when reading about nature, you come across a fact that you would never, ever believe if you were to read it in fiction. A science fiction novel that featured a creature which used its eyes to eat – literally to push food down its throat – would be ridiculous. But that's what frogs do every day.
For some time, people noticed that when frogs are swallowing insects, they closed their eyes. In fact, they more than closed their eyes. Their eyes seemed to shrink back into their head. Researchers thought the eyes perhaps played a part in the swallowing process. A group of scientists took a closer look and proved that, while eating, frogs retract their eyes into their head, and use their eyeballs to push the crickets down their throats. Oh my god.
According to the paper, published in The Journal of Experimental biology, frogs need their eyes to push down crickets as small as a centimeter and a half:
"During swallowing, cineradiography shows that the eyes and associated musculature retract well into the oropharynx and appear to make contact with the prey item. This contact appears to help push the prey toward the esophagus, and it may also serve to anchor the prey for tongue-based transport. . . . Our results indicate that, in Rana pipiens feeding on medium-sized crickets, eye retraction is an accessory swallowing mechanism that assists the primary tongue-based swallowing mechanism."
It appears that frogs only have teeth along their upper jaw. That makes a lot of sense. Any frog with teeth along its lower jaw, might, in a clumsy moment, bite its own eyeball. And the only thing more horrific than eating with one's eyeballs? Is eating one's eyeballs.
Images: Esteban Alzate