Glass frogs are small tree frogs from Central and South America whose belly skin is so translucent you can see the heart, liver and gut through it. They make up the family Centrolenidae, usually measure 3 to 7.5 cm (about 1.2 to 3 inches), live in trees along forest streams, and are active at night. The female lays eggs on a leaf hanging over the water, and the male guards them.
Here’s what makes them so unusual.
What is a glass frog? #
“Glass frog” is the common name for the whole family Centrolenidae, which contains a dozen genera and many species. According to Wikipedia’s glass frog article, they’re found in the rainforests of Central America and Colombia, with the range extending through the Andes as far south as Bolivia.
Most species are green on top, which blends in with leaves. The see-through part is underneath. Glass frogs count among the five main groups of tree frogs, alongside true tree frogs, shrub frogs, reed frogs and Madagascar’s Boophis frogs. Our tree frog facts cover the rest of that crowd.
Why can you see through a glass frog? #
The skin on a glass frog’s belly lets light pass through. Wikipedia describes it this way: the internal viscera, including the heart, liver and gastrointestinal tract, are visible through the skin. Look at one from below, sitting on a leaf, and you can see its organs, including the heart.
The usual explanation is camouflage. A frog with a translucent underside sitting on a green leaf lets some of the leaf’s color show through, so its outline is harder for a predator to pick out. It doesn’t make the frog invisible, but it softens the shape hunters look for.
Do glass frogs hide their blood? #
Yes, and it’s one of the stranger facts about them. Blood is red and opaque, which would spoil the see-through effect. The glass frog article notes that when resting, glass frogs conceal blood in their livers to enhance camouflage. Pulling the red blood cells out of circulation while they sleep makes them more transparent during the day, when they’re resting on leaves in plain view.
When they wake up at night to hunt, the blood goes back into circulation.
How big are glass frogs? #
Small. Most species run 3 to 7.5 cm (1.2 to 3 inches) long. Fleischmann’s glass frog, one of the best-known species, is even smaller: males measure 19 to 28 mm and females 23 to 32 mm, roughly the length of a thumbnail to the first joint. It ranges from southern Mexico through Central America to Ecuador, including Costa Rica, Panama and Colombia.
Where do glass frogs live? #
In humid forests along streams, from southern Mexico through Central America and down the Andes. They spend their lives in the trees and shrubs over running water, which ties into how they breed. They’re mainly nocturnal and hunt small invertebrates at night.
How do glass frogs raise their young? #
This is where glass frogs stand out among amphibians. The female lays her eggs on a leaf hanging over a stream, and the male guards them. Fleischmann’s glass frog males sit on the clutch, turn it and handle the jelly around the eggs. Wikipedia describes the arrangement as protecting the developing eggs from predators in the water.
When the tadpoles hatch, they drop from the leaf into the stream below, where they grow before returning to the trees as adults. For how long that stage takes in different frogs, see how long it takes a tadpole to become a frog.
Are glass frogs endangered? #
Many species are under pressure. Wikipedia notes that climate change and habitat fragmentation threaten the family, with some researchers arguing for higher threat classifications. All glass frogs are covered by CITES, the international treaty that regulates the wildlife trade, so trading them across borders needs permits.
Because glass frogs depend on shaded, clean streams for breeding, losing the forest along a stretch of river can remove a local population.
Can you keep a glass frog as a pet? #
It’s not a good idea for most people. Glass frogs are tiny, delicate, need high humidity, and are protected under CITES, so any legal trade needs permits. If you want to see one, a zoo or aquarium with an amphibian exhibit is the better route, and many support conservation programs for tropical frogs.
Is there a glass frog in Frog Pond? #
Yes. In Frog Pond, a cozy idle game about building a frog colony, the Glass Frog is the fifth of eight worker tiers. Its in-game description is “See-through. Catches what others can’t.” It arrives at Pond Level 7, costs 130,000 coins and makes 260 coins a second at base, and a rare Crystal Glass Frog variant can hatch from a Mystery Egg to boost the whole tier by 50%. The game also has poison dart frogs, bullfrogs and tree frogs, each loosely based on the real animal.
Frequently asked questions #
Are glass frogs completely see-through? #
No. Their backs are usually green and fairly opaque. The belly is the translucent part, and that’s where you can see the organs.
Can you see a glass frog’s heart? #
Yes. The heart is among the organs visible through the belly skin.
Are glass frogs poisonous? #
Glass frogs aren’t known for toxic skin the way poison dart frogs are. Their main defense is camouflage.
Where can I see a glass frog in the wild? #
In humid forests along streams in Central America and northern South America. Look at night, on leaves over running water, which is where they rest and where the males guard eggs.