The idea of a purple snake is captivating, but a snake of solid, true purple pigment does not exist in nature. However, a violet or deep blue-violet hue can be observed in certain species. This surprising coloration is not due to purple pigments in the skin but is an optical illusion caused by the way light interacts with their unique scales. The rarity of this color naturally raises questions about whether these striking reptiles are venomous or poisonous.
The Science Behind Snake Coloration
Snake coloration is determined by specialized cells called chromatophores found in the skin’s dermis layer. These cells contain pigments that absorb and reflect different wavelengths of light to produce color. Melanophores contain the dark pigment melanin, producing black and brown hues, while xanthophores and erythrophores hold pigments that create yellow and red colors, respectively.
The visual effect of purple or blue is primarily the result of a process known as structural color, not pigment. This color is generated by iridophores, which are cells containing microscopic, light-reflecting crystal platelets. When light hits these highly organized structures, it is scattered and refracted, creating wavelengths that appear blue or, when combined with underlying pigments, can look violet or purple.
This structural mechanism, known as iridescence, causes the color to shift and shimmer as the snake moves or the angle of light changes. The dark base color provided by melanophores beneath the iridophores enhances this effect. Since the natural pigments needed to create a pure purple are absent in snakes, the color is typically a short-lived optical effect rather than a fixed hue.
Specific Snakes That Appear Purple
The most famous example of a snake exhibiting a purple or rainbow sheen is the non-venomous Sunbeam Snake (Xenopeltis unicolor), native to Southeast Asia. This snake typically has a dark, uniform body, but its smooth, highly polished scales are responsible for the dramatic optical display. Each scale acts like a tiny prism, scattering light into a spectrum of colors that includes blues, greens, and a noticeable violet-purple.
This effect is so pronounced that the snake is often called the iridescent snake in its native range. The Sunbeam Snake is a burrowing species, spending much of its time underground in loose soil and leaf litter. Its fossorial lifestyle suggests that the iridescence is not primarily for camouflage but may be an incidental result of the scale structure that aids movement through the soil.
Other species can also exhibit a purple tint, though less dramatically than the Sunbeam Snake. Certain color morphs of the non-venomous Aurora House Snake (Lamprophis aurora) can show shifting hues bordering on violet. The Brazilian Rainbow Boa (Epicrates cenchria) also displays iridescence, which can momentarily flash purple within its spectrum. In all these cases, the purple appearance is an illusion of light refraction, not a true purple pigment.
Venomous Status of Purple-Hued Species
The most commonly cited “purple” snake, the Sunbeam Snake (Xenopeltis unicolor), is non-venomous. It subdues its prey, which includes small mammals and other reptiles, through constriction. When threatened, the Sunbeam Snake may bite defensively, but it poses no medical threat to humans beyond a minor wound.
The other iridescent species that may appear purple, such as the Brazilian Rainbow Boa and the Aurora House Snake, are also non-venomous constrictors. While some venomous species, like the Blue Malaysian Coral Snake, possess striking coloration, their colors are generally more fixed and less dependent on the structural iridescence that creates the purple illusion. The snakes most frequently associated with a purple sheen are harmless to humans.
These iridescent species confirm that a striking appearance does not indicate danger. Their defensive behaviors usually involve trying to escape, vibrating their tail, or releasing a foul-smelling musk. The primary concern with a snake bite is not from a purple-hued species, but from the many other venomous snakes that do not display this structural color effect.
Clarifying Venom Versus Poison
The terms “venomous” and “poisonous” are often used interchangeably, but they describe two distinct mechanisms of toxin delivery. Venom is a toxin that is actively injected into a victim, typically through a bite or a sting, as seen with fangs in snakes or a stinger in scorpions. The toxin must enter the bloodstream or tissue to cause harm.
Poison, in contrast, is a toxin that is passively delivered, usually through ingestion, inhalation, or absorption via skin contact. Snakes are overwhelmingly venomous, using their toxins offensively to immobilize or kill prey.
Only a few rare snake species are considered truly poisonous, acquiring the toxins from their diet. For example, certain garter snakes can retain toxins from consuming poisonous newts. The correct biological term for a toxic snake is venomous, as their danger is delivered through specialized fangs.