Snakes exhibit remarkable coloration, leading many to wonder if vibrant shades, like purple, exist in their natural palette. The question of whether a truly purple snake roams our planet is complex, involving the intricate science behind how these reptiles get their diverse appearances.
How Snakes Get Their Color
Snake coloration is primarily determined by two distinct biological mechanisms: pigmentary colors and structural colors. Pigmentary colors arise from specialized cells called chromatophores, which produce and store different types of pigments. Melanophores, for instance, contain melanin, a pigment responsible for black, brown, and sometimes grey hues, and their density influences the lightness or darkness of the skin. Xanthophores produce yellow to orange colors through pteridine pigments, while erythrophores contain carotenoid pigments that contribute to red and orange tones. The presence, absence, or combination of these pigments in varying concentrations creates a wide range of colors seen in many snake species.
Structural colors, on the other hand, are not due to pigments but rather the way light interacts with the microscopic structures of the snake’s scales. These structures, often found within specialized cells called iridophores, contain guanine crystals arranged in precise layers. When light strikes these layers, it is refracted and reflected, causing certain wavelengths to be amplified while others are canceled out, a phenomenon known as thin-film interference. This process can create shimmering, iridescent effects, as well as colors like blue and green, which are rarely produced by pigments alone in snakes. The angle at which light hits the snake, or the viewing angle, can cause these structural colors to shift and appear different.
The Elusive Purple: Appearance vs. Reality
While true pigment-based purple is exceptionally rare or absent in snakes, some species can appear purple due to the interplay of structural coloration and underlying pigments. The Brazilian Rainbow Boa (Epicrates cenchria) is a prime example, displaying an iridescent sheen that shimmers with various colors, including purplish tones, under specific lighting conditions. This effect results from light bending and scattering through microscopic ridges and layers within their scales, creating a shifting, reflective quality. The appearance of purple in these snakes is an optical illusion, where blue structural colors combine with other reflected light to give a purplish impression.
Genuine purple pigment is not typically found in snakes. However, rare genetic variations can lead to a purplish hue in some individuals. Genetic mutations that reduce or alter the production of yellow and red pigments, or modify the arrangement of reflective cells, can result in a purplish tint when combined with existing blues or greys. The “Lavender” morph of the corn snake (Pantherophis guttatus), for example, exhibits grey blotches on a pinkish background due to a gene mutation affecting pigment and crystal storage, which can sometimes give a subtle purplish cast. These instances are typically not a vibrant, pure purple but rather a muted or pastel purplish shade.
Beyond Purple: Other Striking Snake Colors
Beyond purple, the world of snakes showcases an impressive spectrum of other vivid and unusual colors. Bright blues are seen in species like the Blue Insular Pit Viper (Trimeresurus insularis), where structural coloration creates the azure hue without blue pigments. Intense reds and oranges are common in various species, often produced by carotenoid and pteridine pigments, as exemplified by many corn snake morphs. These diverse colors serve various purposes in snakes, including camouflage, warning signals, or communication within their species.
The genetic variations that lead to these striking colors often involve modifications in the production, distribution, or interaction of pigments and structural components. For instance, specific genetic mutations can lead to the absence of certain pigments, such as the lack of melanin in albino snakes, resulting in white, yellow, or red coloration. This diversity underscores the specialized conditions required for any particular color, including the elusive purple, to manifest in nature.