Terrestrial transparent animals are rare, due to the fact that red blood cells in the blood absorb green light and reflect it, making the circulatory system highly visible, especially against green foliage.
However, one terrestrial vertebrate, the glass frog, is able to change its body color and become transparent while sleeping.
A recent study published in the journal Science describes the trick to making glass frogs transparent.
Scientists use an imaging technique called photoacoustic microscopy (PAM) to track the blood circulation of glass frogs as they sleep.
They irradiated the glass frog with a green laser, and the red blood cells in its body absorbed the light energy and emitted ultrasound waves that were picked up and tracked by acoustic sensors.
The study found that the glass frog was able to filter close to 90 percent of its red blood cells out of its blood vessels and store them in its liver.
When the glass frog returns to an active state from sleep, the red blood cells flow out of the liver and re-enter the circulation.
Scientists plan to study how glass frogs avoid clotting during that process next.
