Glass Frog
Its skin is transparent — you can see its beating heart, liver, and eggs through its stomach
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Superpower
Glass frogs have translucent skin on their underside through which internal organs are directly visible — a beating heart, pulsing liver, developing eggs, and the entire digestive tract. A 2022 study revealed the mechanism: glass frogs achieve transparency while sleeping by hiding up to 89% of their red blood cells in their liver, which has reflective crystals that scatter light. When active, the red blood cells re-enter circulation and the frogs become more opaque. It's the first known example of an active transparency mechanism in a vertebrate.
Overview
There are around 160 species of glass frogs in the family Centrolenidae, found in the rainforests of Central and South America. They live in trees and shrubs along streams, and males guard egg clutches laid on leaves overhanging water — when eggs hatch, tadpoles drop into the stream below. Despite their remarkable transparency, they're well camouflaged from above — their backs are green and match leaves perfectly. The transparent belly faces downward toward whatever surface they're clinging to, making them nearly invisible from below against the bright sky.
Found in
Rainforests of Central and South America, from southern Mexico through Bolivia and Argentina. Most diverse in the cloud forests of the Andes. Live on vegetation along fast-moving streams at elevations from sea level to 3,000m.
Things worth knowing
- 1
The 2022 study on glass frog transparency found they store red blood cells in their liver while sleeping — the liver contains reflective guanine crystals that scatter incoming light, making the stored cells invisible. It's the only known example of an animal actively manipulating its own transparency.
- 2
Male glass frogs are devoted fathers — they guard egg clutches for weeks, keeping them moist by pressing their body against them, and actively defending against wasps and flies that would parasitize the eggs.
- 3
Some glass frog species are so transparent that the heart is visible pulsing in real time through the chest wall — researchers have used living glass frogs as non-invasive models for studying cardiac function.
- 4
Despite the transparent belly, glass frogs are nearly impossible to spot from above — their dorsal coloration matches green leaves so precisely that they're cryptic from both directions simultaneously.
- 5
Glass frogs actively choose leaves that overhang fast-moving water for egg-laying — the sound of the stream masks their calls from predators, and the position ensures tadpoles land in moving water when they hatch.