A Blue Green Snake

Rough green snakes, Opheodrys aestivus, are common in the southeast.  These small snakes are bright green on their backs and sides with a yellowish-white belly.  They are among the most arboreal of the snakes in this region, climbing through the branches of trees and shrubs where they hunt insects and other invertebrates.  The largest rough green snake might be two feet in length.  They are called rough because their scales have a ridge running down the middle (the keel) that gives them a rough feel when handled.  These snakes are good-natured and don’t bite if you pick them up to see how rough they are. 

Rough green snake (Opheodrys aestivus) showing its bright green color

Diane and I regularly see rough green snakes while walking the local greenway.  They are hard to see when they climb in the vegetation because their green color is the perfect camouflage.  These snakes often cross the paved greenway trail and that is where we can get good looks.  Recently we found a dead rough green snake, killed by a car, on the side of the road at greenway’s end.  The funny thing was, this green snake was partially blue in color.  It turns out that rough green snakes turn blue when they die.  The reason they turn blue after expiring gets into the mystery of color.

Vertebrates have a hard time making themselves green.  Unlike plants that make the green chlorophyll pigment to run photosynthesis, green snakes, lizards and birds must use two different means to turn green.  Their green color is usually a combination of yellow from a carotenoid pigment and blue produced from the structural elements of their skin or feathers.  This combination of pigment color and structural color works for green snakes, green lizards and green birds. 

Pigments molecules absorb certain wavelengths of light and that gives them their color.  Chlorophyll can be extracted from plants and still retain the green color.  Structural color is different.  It depends on the physical arrangement of small particles that refract certain wavelengths of light to produce color.  In many cases with structural color in animals, you need to view the subject from a certain angle for the color to be revealed. Eastern Bluebirds appear blue because tiny granules in their feathers refract blue light to the viewer.  In some light conditions bluebirds will appear black because the refraction does not occur.  Ruby-throated Hummingbird throats may appear dull from one angle, but as the bird turns a brilliant flash of red will shine out.  You cannot extract blue pigments from the feathers of bluebirds and you cannot extract red pigments from the throat feathers of hummingbirds.  Both these are examples of structural color.  

Rough green snakes have cells in their skin that contain a crystalline arrays of guanine, one of the components of nucleic acids.  The arrangement of the guanine crystals in these cells refract blue light.  Also in the skin of rough green snakes are cells that have yellow pigments that reflect yellow light.  Just like in an elementary school art class, yellow plus blue gives green. 

 

Dead rough green snake (Opheodrys aestivus)  with green regions and blue regions.

When a rough green snake dies, the yellow pigment begins to break down. The blue refracting crystals are more stable so the dead green snake gradually turns blue as the yellow pigment is degraded.  This was the state of the dead snake we found.  In some parts of its body the yellow pigment remained so it looked green in others the yellow pigment was lost and only the blue shone through.