Their delicate, greenish transparent forms don’t cast shadows, rendering them almost invisible to birds and other predators passing overhead or underneath.
But when northern glass frogs wake up and hop around in search of insects and mates, they take on an opaque reddish-brown color.
“When they’re transparent, it’s for their safety,” said Junjie Yao, a Duke University biomedical engineer and study co-author.
A male glass frog photographed from below using a flash, showing its transparency.
“Transparency is super rare in nature, and in land animals, it’s essentially unheard of outside of the glass frog,” White said.