Yes, some snakes exhibit a visible glow when exposed to a black light, a phenomenon known as biofluorescence. A black light emits long-wave ultraviolet light, specifically in the UV-A range, which is mostly invisible to the human eye. This UV-A radiation interacts with specific compounds in the snake’s body. The resulting emission of visible light, often blue or green, is a chemical reaction to the external energy source, not light produced by the snake itself. This biological trait is more widespread across reptiles than scientists initially understood.
The Phenomenon of Biofluorescence in Snakes
Biofluorescence has been documented across diverse snake families, suggesting it is a common trait. Pitvipers, such as certain species of rattlesnakes and Trimeresurus hageni, show fluorescence, often concentrated on their tails or rattles. The glow is not limited to terrestrial species; the marine snake Laticauda laticaudata has also been observed to fluoresce.
The glow often originates from the keratin layer of the scales, the same protein that forms human hair and nails. In some pythons, including the Reticulated python and the Ball python, the lighter patches of skin fluoresce brightly. The colors observed under UV light usually fall into the blue, bluish-green, or greenish-yellow spectrum.
In some cases, the fluorescence is not primarily in the skin but in the underlying skeletal structure. Studies on deceased specimens show that the bones of many snake families emit a bright blue or green light under UV exposure. It remains uncertain if this skeletal glow is visible through the living snake’s skin and scales, but this highlights the diverse biological sources of light emission.
How Black Light Causes Snakes to Glow
The mechanism behind this visual effect is the process of fluorescence, which involves the absorption and re-emission of light energy. When a black light emits invisible UV-A photons, these high-energy packets of light strike specific molecules in the snake’s tissues called fluorophores. These fluorophores, which can be pigments or structural proteins like keratin, absorb the energy from the UV light.
Absorbing the UV photon temporarily excites the electrons within the fluorophore molecules, pushing them to a higher energy state. This excited state is unstable, and the electrons immediately drop back down to their original, lower-energy state. As they return, they release the absorbed energy, but a small amount is lost as heat.
Because some energy is lost, the light that is re-emitted has a longer wavelength and lower energy than the absorbed UV light. This shift converts the invisible UV-A radiation into visible light, which is what the human eye perceives as a glow. This process is distinct from bioluminescence, where an organism generates light through a chemical reaction, and phosphorescence, where the glow persists for a long time after the light source is removed.
Biological Function and Evolutionary Significance
The purpose of biofluorescence in snakes is not fully understood, and it may be a simple byproduct in many species. The fluorescent compounds are often incidental to other biological processes, such as pigment metabolism or keratin structure. This suggests the glow is an accidental result of their chemical makeup rather than an evolved trait for communication.
For pitvipers, the fluorescence observed on the tail tip has led to a compelling hypothesis linked to their hunting behavior. Many pitvipers employ “caudal luring,” wiggling their tail to mimic a small insect or worm to attract prey like frogs or lizards. The blue or white fluorescence of the tail may enhance this lure, making it more visible to prey species that can see UV light, possibly mimicking naturally occurring UV-fluorescent insects.
Other possibilities include using the glow for species recognition or mating signals, though this is less likely for many nocturnal species with limited visual acuity. Since the phenomenon relies on an external UV light source, its function in the natural environment depends entirely on the presence of UV light, such as during twilight or in specific shaded habitats. The function remains a subject of ongoing research.