Smaug the dragon or frog with an eye to die for?

BENEATH the translucent gold vein-like structure lies what looks like the eye of Smaug. But this is no dragon’s eye. It belongs to something much smaller&colon; a teacup-sized frog having a nap in the trees of a tropical rainforest.

The red-eyed tree frog (Agalychnis callidryas) lives all over Central America and the Caribbean. In the day, when the frog is asleep, a gold membrane creeps over its eyes. It lets in a small amount of light, enough so that if a predator approaches, the non-poisonous frog can wake up, show its bulging red eyes and present its yellow feet in a bid to make the would-be attacker think twice.

Nictitating, or blinking, membranes are found in a variety of animals, from cats and sharks to camels and polar bears. In all the animals that possess them, this extra eyelid moisturises the eye while still letting light through. “A nictitating membrane is found in many mammals, although we humans have lost it,” says zoologist Sue Evans at University College London. “Its main function is to clean and wipe the surface of the eye. In frogs it is basically a modified part of the lower eyelid, and thus modified skin.”