Glass FrogsBy Gerry Bishop
These little creatures are clearly unusual!
It’s nighttime, and you’re walking through a tropical rainforest. Suddenly you hear a tiny cheeep! You shine your headlamp toward the sound and strain your eyes. See anything? Probably not. The creature that made the sound is almost invisible.
What you heard is the call of a glass frog. Why “glass”? Because some kinds of these tiny animals have see-through skin. On the underside of one, you can see its beating heart, blood vessels, bones, and more. Check out the photo at right. If glass frogs like this one went to a doctor, they would never need an X-ray!
On the top side of some glass frogs, see-through skin can create a soft, ghost-like look (below left). The green colors beneath the skin blend with the leaves the frogs often sit on. That hides them from snakes, birds, and other predators looking for a meal. (And from people looking for them with headlamps!)
More than 150 species of glass frogs live in the rainforests of Central and South America. During most of the year, they hop among the tree branches, looking for insects, spiders, and other tiny creatures to eat. They hunt at night, using their big eyes to see in the dark. Unlike most other frogs, glass frogs have eyes that face forward—all the better for seeing prey right in front of them.
At the start of the mating season, usually on rainy nights, male glass frogs head toward the closest stream. They settle on branches that hang over the water. And then the songs begin.
Peeeep, chirrrrp, tweeeet—the frogs’ high-pitched calls drift through the forest. Each frog has blown up the skin on its throat like a balloon. Air in the sac makes the frog’s sounds louder—perfect for calling for mates and warning other males to keep away.
Most other kinds of frogs mate and lay their eggs in a pond or stream. There the eggs hatch into tadpoles, which then turn into baby frogs. But for glass frogs, mating and egg-laying happen above a stream.
As a female lays her eggs on the underside of a leaf, the male fertilizes them. Then the female leaves, and maybe the male does, too.
But for some species of glass frogs, the male sticks around. His job is to care for the eggs as best he can. The eggs need to stay moist, and steady rains usually take care of that. But during dry spells, Father Frog may have to cover them with his moist body. And if that’s not good enough, he may even pee on them!
Ninja Frog on Guard
The male also guards the eggs from attack. If a hungry wasp comes for a snack, for example, he’ll kick like a ninja fighter to fend it off.
But sometimes a predator is too much for even a ninja frog to handle. A bird, larger frog, or even a big spider may kill and carry off the brave defender. Or a snake may come by and gulp down the frog and his eggs. But up and down along the stream, other glass frogs are winning their battles. They, and their precious eggs, will survive.
It’s Raining Tadpoles!
At hatching time, tiny tadpoles wriggle from their eggs. Then the jelly covering them starts to turn to liquid. One by one, two by two, the tadpoles drip off the leaf and plop down into the stream below.
There the tadpoles dive down among the stones and muck on the stream bottom. For nearly a year, they hide there, growing legs and lungs and eventually losing their tails. Finally the little frogs crawl out of the water and up into the treetops. There, nearly invisible, they go about their little glass-frog lives.
“Glass Frogs” originally appeared in the August 2015 issue of Ranger Rick magazine.
(Click on each image above for a closer view of the story.)