Why do Green Tree Frogs Change Color?

Have you stopped by the Nature Center and met our green tree frog ambassadors Harvey and Hopper? You may have noticed that some days they are bright green and others they are a dark grayish brown and wondered, why? What changed? 

A frog’s skin has two layers: the epidermis and dermis. The dermis layer contains color producing cells like chromatophores, iridophores and melanophores. The chromatophores have yellow and red pigments, the iridophores have crystal platelets and the melanophores have brown and black pigments. The frog's cells will absorb most light colors, but the platelets in the iridophore scatter and reflect blue light back through the yellow pigments in the chromatophores and produce green. 

Likewise, when the frog gets cold, chemical signals from the pituitary gland cause the iridophore platelets to contract, making it difficult for light to get through the platelets to be reflected. The contracting platelets create room for the black pigments to disperse throughout the melanophore. Since the blue light is not being reflected through the contracted platelets, the yellow and black pigments come together to make gray/brown. 

A lot of different things can cause the frog to change color besides just temperature in the example above. Tree frogs can decide to change color to blend in more with their surroundings as a means of protection from predators and to give themselves an advantage to catch prey. They might also choose to change color in response to available sunlight and humidity. On a hot, dry afternoon it will choose a greener color to reflect sunlight and stay cool while on a colder and damp morning it will choose a darker tone to help warm up. 

Turns out, green tree frogs are just nature’s mood rings. So the next time you spot a green tree frog changing its tone, just remember, it’s not magic, it’s biology with a splash of style.