The Glass Frog Diverts Its Blood Flow to Activate Invisibility

If you've ever seen a frog with skin so see-through you can spot its organs, you’ve stumbled into the world of the glass frog. Found mostly in Central and South America, these wild little amphibians belong to the family Centrolenidae. The glass frog's transparent skin makes it a marvel of evolution, not one of your average tree frogs.

Like other frogs, glass frogs go through an aquatic larval stage, but their adults perch high in shrubs hanging over forest streams, often blending in perfectly with the green leaf they're resting on.

The backs of most glass frogs are typically primarily lime green, while the undersides are translucent, offering a living window into their internal organs. This makes them excellent models for studying frog's internal processes, including how their red blood cells behave.

Here's Why Glass Frogs Are Clear

underside of glass frog — These frogs can concentrate their red blood cells in the liver while resting, reducing the red coloration that might make them easier to see. Robert Pickett / Getty Images

The biology glass frogs exhibit is as remarkable as their looks. Through a combo of edge diffusion and a flattened body posture, the frog's edge appears softer and helps it camouflage better. That soft blur makes it harder for predators like birds to spot them against darker or lighter foliage.

Glass frogs are currently the only known animals to demonstrate this translucency-based camouflage mechanism, making it a unique adaptation.

Even cooler? These frogs can concentrate their red blood cells in the liver while resting, reducing the red coloration that might make them easier to see. It’s transparency with a purpose—evolution’s version of an invisibility cloak.

The glass frog’s body evolved over time to support this transparency, and scientists are actively studying this unique trait to understand its underlying biological mechanisms.

Over 160 Species of Glass Frogs

There are many species of glass frogs — around 160 in total — including the reticulated glass frog and several species found in Colombia, all of which belong to the same family (Centrolenidae) of opaque and translucent frogs.

Scientists determine species limits using mitochondrial and nuclear genes, helping clarify how these different species are related.

Glass frogs likely originated in South America and spread to Central America, with regions like Costa Rica being hotspots for species richness. These leaf-sitting neotropical frogs often cling to the undersides of leaves.

Unlike other tree frogs in the family Hylidae (whose eyes face sideways), glass frogs have eyes that face forward.

Reproductive Roles and Glass Frog Behaviors

Glass frog reproduction involves unique roles: Glass frog females lay egg clutches on leaves above water, and glass frog males stay behind to guard them.

This parental investment by male glass frogs includes defending against predators, fly species and parasitic maggots that target the eggs. The glass frog females brood the eggs only during laying, leaving the rest of the duty to the males.

Eggs clutches deposited during mating season eventually hatch, and once the tadpoles fall into streams, they continue their aquatic development. These strategies help protect the next generation of these smaller frogs from common threats like invasive species, predators and habitat loss.

Conservation and Public Awareness

As beautiful as they are, glass frogs face real challenges. Many are considered endangered species due to shrinking habitats and climate change. Their delicate nature also makes them sensitive to environmental changes that can disturb frogs health.

Conservation programs at places like the Henry Vilas Zoo aim to educate the public and support research on preserving these frogs and their natural history.

Photographs showing glass frogs with visible internal organs — even during mating — highlight the frogs’ unique anatomy and remarkable transparency, offering insight into their evolution. Even aspects like how maggots feed on unattended eggs help illustrate the fragile balance these amphibians maintain.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.