When little glass frogs enter the night, they can become transparent by hiding nearly 90 percent of their red blood cells.
Different spots are tucked inside the frog’s liver that can hide the cells, according to a Thursday study in the journal Science.
During the day, these little frogs spend hours hanging under tree leaves. At this point, their green-colored forms don’t cast shadows, making them mostly invisible to potential predators.
When little glass frogs enter the night, they can become transparent by hiding nearly 90 percent of their red blood cells. Above: A female glass frog is shown with eggs in transparent ovaries, photographed from below using flash
But when they wake up, the blushing frogs look more tone-brown.
“When it’s clear, it’s for health,” said Junjie Yao, the university’s chief biomedical engineer and co-author of the study. When they are awake, predators can actively flee, but when they are asleep and most vulnerable, they are ‘fit to hide.’
Scientists have used light and ultrasound imaging technologies to unlock a new insight: frogs can “shrink,” or hide, nearly 90 percent of their red blood cells in their livers when they sleep.
That circulating blood gave them in a different way; Yao also points out that frogs can squirm and squish most of their guts together.
The research “nicely explains” how “glass frogs hide blood in their livers to keep it transparent,” Juan Manuel Guayasamin, a frog biologist at the University of San Francisco de Quito, Ecuador, who was not involved in the study, told The Associated Press.

Different spots are tucked inside the frog’s liver that can hide the cells, according to a Thursday study in the journal Science. Above: A glass frog sits on a leaf

Scientists have used light and ultrasound imaging technologies to unlock a new insight: frogs can “shrink,” or hide, nearly 90 percent of their red blood cells in their livers when they sleep. Above: a male glass frog photographed from below
How they are able to accomplish this feat is somewhat of a mystery.
For most animals, with a minimum of oxygen circulating in the blood for several hours, they would be lethal – and blood clotting so closely would result in a fatal coagulation. However, frogs can survive.
The researchers believe that future studies could provide specific information for the development of anti-blood clotting drugs.
“Clearness is rare in nature, and unheard of in land animals, outside of the glass frog,” said Oxford University biologist Richard White, who was not involved in the study.
There are fishes, shrimps, jellies, worms, and insects, none of which move large quantities of red blood through their bodies.
‘This is a really amazing, dynamic form of camouflage,’ White said.

“Clearness is rare in nature, and unheard of in land animals, outside of the glass frog,” said Oxford University biologist Richard White, who was not involved in the study. Above: The front of the glass frog’s habitat is seen

Above: A collection of images from the researchers shows the same frog in sleep, under anesthesia and while active (transmitted in light), showing the difference in red blood cells in the circulatory system.
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