Glassfrogs Hide Their Blood to Turn Transparent and Stay Safe from Predators

Glassfrogs got their name because their bellies are as see-through as Cinderella’s slipper. From below, you can even see their internal organs and bones. This may not sound like the best strategy to stay safe, but it turns out that in order to camouflage, the frogs can pull most of their blood out of their veins. This means they don’t cast any shadows when clinging to the underside of leaves (obligatory cute sleepy frog photo below) when they sleep during the day. The glassfrogs manage to move 89% of their blood into their liver before nodding off. Then they redistribute it throughout their body when they wake up, without any ill effects. Understanding the process could lead to advances in how we treat blood clots in humans.

Glassfrogs clinging to the underside of a leaf
Jesse Delia

The frogs are generally nocturnal and need a way to hide from predators when they sleep during the day. They’re green on top to blend in. But in the lab, they cling to a petri dish instead of a leaf. The scientific study, which we saw in Smithsonian Magazine, uses lasers and sound waves to see inside the glassfrogs in a noninvasive way. The team included researchers at multiple universities and the American Museum of Natural History.

Side by side comparison of the blood cells inside a frog that is sleeping versus under anesthesia
Junjie Yao, Duke University

As shown in the image above (right), blood is distributed throughout the body when the frog is under anesthesia. But if the frog goes to sleep naturally, as shown on the left, the blood is mostly in the liver. The map of its blood vessels is much more faint because there’s only a small fraction of blood left in the rest of its body. The peer-reviewed journal Science published the results.

The underside of a glassfrog, with its internal organs showing through translucent skin
Jesse Delia

For more frog science, check out the pumpkin toadlets that aren’t very good at jumping. Or learn more about the mutual benefits of frog and tarantula friendships.

Melissa is Nerdist’s science & technology staff writer. She also moderates “science of” panels at conventions and co-hosts Star Warsologies, a podcast about science and Star Wars. Follow her on Twitter @melissatruth.

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