Glass Frog: The Frog You Can See Through
Glass frogs are small tree frogs from Central and South America with skin so clear that, from below, you can see the heart, liver and gut. In 2022, scientists discovered their best trick: while the frog sleeps, it hides most of its red blood cells inside its liver and becomes up to three times more transparent.
Quick Facts
- Species shown: Northern glass frog, Hyalinobatrachium fleischmanni
- Where: Rainforest streams of Central and South America
- Size: About an inch long
- Active: At night; sleeps on leaves by day
- Famous for: Hiding about 89 percent of its red blood cells in its liver while asleep
Why Is the Glass Frog See-Through?
The skin and muscle on a glass frog's belly let light through. Look from underneath and you can see its organs, including the heart beating. From above, the frog looks green and blends into the leaf it sleeps on.
The Blood-Hiding Trick
Blood is red and absorbs light, which should give a see-through animal away. A 2022 study in Science found the solution. While northern glass frogs sleep, they pull about 89 percent of their circulating red blood cells out of the bloodstream and pack them into the liver, which has a mirror-like covering.
That makes the frog two to three times more transparent. When it wakes at night and starts moving, the red cells flow back out and it becomes easier to see. Scientists are studying how it does this without forming blood clots.
Glass Frog Dads
In many glass frog species, the father guards the eggs, which are laid on leaves hanging over a stream. When the tadpoles hatch, they drop into the water below.
Frequently Asked Questions
Can you really see a glass frog's heart?
Yes. From below, its translucent belly shows its organs, including the beating heart.
How do glass frogs become more transparent?
While asleep, they store about 89 percent of their red blood cells in the liver, which makes them two to three times more transparent.
Where do glass frogs live?
In rainforests of Central and South America, near streams.
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Sources
- Taboada et al., Science 2022: red blood cell storage and transparency
- American Museum of Natural History: how glass frogs hide
- Duke University: the study and its photographs
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Cover photo: Carlos Funes via Wikimedia Commons, CC BY 4.0.