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. 

Alaska Connections

Diane and I recently made a twelve day trip to Alaska with a group of birders from North Carolina and Virginia.  On this trip we would revisit places from our expedition of 31 years ago and go to some new ones.  We saw lots of new land- and seascapes, a Canada lynx and a walrus, a Gyrfalcon and Bristle-thighed Curlews.  We also ran into some plants and plant-ish things I have written about recently in this blog.

Last month I wrote about alders growing near my home.  In Alaska, at Summit Lake on the Kenai Peninsula, the alders were in flower.  Alders in North Carolina flowered in early March but in southern Alaska, June is the flowering season.   The alder we saw in at Summit Lake was Alnus viridis ssp sinuata, the Sitka alder.  This alder is a scrubby tree and grows throughout Alaska, across the Bering Strait into East Asia, along the west coast of North American into northern California and down to the northern Rocky Mountains. The Sitka alder’s leaves are bright green with serrated margins.  The female catkins were green and the male catkins were brown, had already released their pollen but were still on the plant.  Sitka alder is an early colonizer of new land, beginning primary succession.  With global climate change, glaciers are receding at an increased rate.  When the retreating glaciers leave exposed ground, Sitka alders become established.  Their nitrogen-fixing, symbiotic bacteria enrich the soil paving the way for new forest to grow where the glaciers disappeared. 

Sitka alder (Alnus virdis ssp. sinuata)
with catkins of male flowers.

Sitka alder (Alnus viridis ssp. sinuata)
with female catkins

Haircap moss (Polytrichum strictum) gametophytes

The moist forests on the south side of the Alaska Range support a wide variety of mosses.  I wrote about North Carolina mosses  in April.  In Denali State Park we found thick and beautiful stands of Polytrichum strictum, the haircap moss.  This moss has a circumpolar distribution and extends into the lower 48 US states.  Clusters of gametophyte plants produce a green, star-pattern.  The sporophytes, the result of moss sex, have a little hairy cap at their tops, covering the capsule where the spores are waiting to be released. 

Haircap moss (Polytrichum stgrictum) gametophyes
with sporophytes

Kamchatka rhododendron (Rhododendron camtschaticum)
flowering on the tundra

Back in January I posted about lichens in Florida and North Carolina.  Out on the tundra of Denali National Park, where willows are inches tall and tiny rhododendrons (Rhododendron camtschaticum) produce large flowers, we found several species of lichens including the famous reindeer moss.  Reindeer moss is, of course, not a moss but a lichen, that symbiotic organism made of a fungus and an alga.  The lichens pictured here are Cladonia rangiferina (gray reindeer moss) and Cladonia fimbriata (trumpet lichen).  Lichens form much of the diet of caribou, Rangifer tarandus who endlessly graze as they walk the tundra.  Caribou are the same species as the old-world reindeer but have never been domesticated.  These large herbivores can find lichens even in winter.  Caribou use their sharp hooves to expose the lichens below the snow.  Unfortunately we did not see any caribou grazing the lichens of the tundra.   

Reindeer moss, the lichen
Cladonia rangiferina

 

Trumpet lichen Cladonia fimbrata

The differences between the Southeastern US and Alaska are striking.  There is a transition from subtropical to arctic with different habitats, climates, plants and animals. These areas are separated by a distance of more than 3000 miles and 30 degrees of latitude.  But the similarities between the Southeast and Alaska are profound.  Linked by biogeography and the evolutionary history of the inhabitants, the similarities were as striking as the differences.