How glass frogs use sleep to become nearly invisible to predators
In short: Most see-through animals live underwater, but certain jungle frogs have mastered a terrestrial disappearing act. By siphoning their red blood cells into the liver while they sleep, these amphibians can become two to three times more transparent, effectively vanishing into the foliage to avoid being eaten.
The glass frogs of the family Centrolenidae, native to the forests of Central and South America, possess translucent skin and muscles that allow them to blend seamlessly into their environment. While many aquatic species like jellyfish or icefish are transparent because they lack hemoglobin, these land-dwelling amphibians face a significant hurdle: red blood cells absorb a great deal of light, making the animal opaque. This makes their appearance quite striking when they are active. During their nocturnal hours, their veins form a bright red, visible maze.
A recent study published in the journal Science has revealed how these nocturnal creatures solve this problem during their daytime rest. When a glass frog, such as Hyalinobatrachium fleischmanni, enters sleep, it siphons 89 percent of its red blood cells away from its circulatory system and into its liver. To accommodate this sudden influx of cells, the liver actually grows in size by approximately 40 percent.
This biological redirection is aided by a specialized mechanism: the liver is encased in a mirrored sac. These crystal-lined sacs reflect incoming light, further enhancing the frog's camouflage. This process makes the frogs significantly more transparent, a survival strategy researchers believe helps them evade predators while they are inactive. To observe this phenomenon, scientists had to move beyond traditional methods, using photoacoustic microscopy—a technique that uses lasers to detect red blood cells via sound waves—to study the frogs while they were peacefully asleep. This method was essential because studying these animals in a lab is notoriously difficult. Researchers found that they must be happily asleep to observe the transparency.
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Sources
- Summary by Intellect · source: These Frogs Hide Thanks to Transparent Skin
- Also: These Frogs Turn Nearly Invisible While Sleeping
- Also: What makes glass frogs transparent? The secret is in their blood.
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