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Hanging out in the trees of Central and South America are some frogs with pretty unusual coloration. Which is to say, parts of them have no color at all. Their bellies are completely see-through!

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Hanging out in the trees of  Central and South America are some frogs with pretty unusual coloration. Which is to say, parts of  them have no color at all.

Their bellies are completely  see-through thanks to a combination of thin skin and a total lack  of pigment-bearing cells. You can see everything! From their  guts, to their beating hearts.

These frogs are known as glass frogs. And even though their bare-all bellies  look like the perfect buffet preview for predators, their translucency may actually  be an interesting form of camouflage.   There are about 150 species of glass  frogs in the family Centrolenidae. All of them lack pigment on their bellies, and about a quarter of them  are properly see-through.

Their backs are a more familiar hue -- green. That green color helps them  blend into their leafy background so they’re less easily spotted by  hungry birds or other predators. The green in some species  even reflects infrared light which might mess with the senses  of some birds and snakes.

But there also seems to be  a purpose to the clear bits. That’s according to a 2020 paper  published in the journal PNAS. Researchers took photos of the  frogs on leaves or white backgrounds and then analyzed their color  based on what they’d look like in the eyes of birds, snakes, mammals or humans.

They saw that the perceived brightness  of a frog’s green back changes depending on how much light bounces  off the leaf the frog is sitting on. The leaf color essentially shines  through the frog’s translucent underside helping them blend in. And because some of the translucent  parts are visible from above, it literally blends their  edges into the background making it tricky for a predator to  see a nice, clear, froggy outline.

It’s like the frogs are using the  blend and blur tools in Photoshop. The researchers dubbed this  camouflage technique edge diffusion. And in their study, the froggy  camouflage seemed to fool both people and wild animals.

The researchers created a Where’s  Waldo-style experiment where they randomly hid images of frogs with different  patterns and degrees of see-throughness on a leafy background. And it took people longer to find frogs  that looked most like the real life ones, with translucent legs and opaque  bodies, than fully opaque frogs. Then, because you can’t ask animals to  look at a picture book, the scientists also made frogs out of gelatin that  were either opaque or see-through.

And they plonked them on leaves  in the frogs’ natural habitat to see which ones would be picked  off by predators the quickest. And the opaque frogs became gummy snacks quicker and more often than the clear ones. Scientists have thought for a while that  these bare bellies might help the frogs camouflage themselves, but this is the  first study to actually show how it works.

And this blending strategy actually seems  to be pretty different than other forms of camouflage, like changing color  or being totally see-through. So it just shows you how many  ways life has learned to use color and light to its advantage, even when  it means putting everything on display! Thank you for watching this episode  of SciShow, which in the interests of transparency we have to tell you  was supported by our patrons.

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