Pictured here is Glendy, a male Arizona Black Rattlesnake, at his darkest and lightest.
Like many snakes, Arizona Black Rattlesnakes (Crotalus cerberus) undergo morphological color change as they age. What is illustrated here is rarer in snakes; physiological color change is probably most well-known in chameleons, but Arizona Black Rattlesnakes can do this too!
What’s the difference? Morphological color change is a gradual process where the number or quality of cells that produce color (chromatophores) changes; it can take years. Physiological color change is a rapid shift due to the movement of pigment within chromatophores — dramatic changes in color can happen in minutes or even seconds! Arizona Black Rattlesnakes can change from their darkest to lightest color in minutes. Not quite as rapid as chameleons, but still impressive.
Watch carefully and see Boyett, another male Arizona Black Rattlesnake, change color in this timelapse video:
We presented a poster on this phenomena for the Snake Ecology Group in 2009 that you can see here.