Why Frogs are Green

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Pine Barrens tree frog. (Image credit: USFWS)

Kermit the Frog often said being green isn’t easy. He had no idea how complex it really is.

Three types of pigment cells, called chromatophores, work together to make a frog green.

((ImgTag||right|null|null|null|false))On top of these cells sit iridophores.  Although iridophores don’t actually produce pigmentation, they reflect light off of the surface of purine crystals inside the cells. When light hits these cells, they produce a silvery iridescent reflection in frogs, as well as other amphibians, fish and invertebrates. 

In most green frogs, sunlight penetrates through the skin to the little mirrors in the iridophores. The light that reflects back is blue.

The blue light travels up to the top layer of cells called xanthophores, which often contain yellowish pigments. The light that filters through the top cells appears green to the human eye.

Frogs without xanthophores look bright blue.

Many frogs depend upon their skin color for defense against predators.

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The layers of pigment cells can alter the color of a frog’s skin from bright green to dark brown. This talent helps a frog blend in with its environment.

The cells are contortionists. Hormones in the frog can change the cells’ shape, move around the pigment inside the cells, and alter the intensity of light coming from them. 

As a frog leaps from a bright green leaf to a muddy brown pond, the cells in its skin adjust the frog’s hue to match and keep the frog hidden.  

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Corey Binns
Corey Binns lives in Northern California and writes about science, health, parenting, and social change. In addition to writing for Live Science, she's contributed to publications including Popular Science, TODAY.com, Scholastic, and the Stanford Social Innovation Review as well as others. She's also produced stories for NPR’s Science Friday and Sundance Channel. She studied biology at Brown University and earned a Master's degree in science journalism from NYU. The Association of Health Care Journalists named her a Centers for Disease Control and Prevention Health Journalism Fellow in 2009. She has chased tornadoes and lived to tell the tale.