Light exists across a vast electromagnetic spectrum, yet human eyes perceive only a small fraction, known as visible light. This narrow band includes colors from red to violet. Beyond violet lies ultraviolet (UV) light, which possesses shorter wavelengths and higher energy than what we can see. While invisible to us, many animals possess the ability to detect and utilize UV light, revealing a world of colors and patterns unseen by humans.
Perceiving the Invisible Spectrum
Ultraviolet light spans wavelengths ranging from 10 to 400 nanometers. Our inability to see this portion of the spectrum is due to the human eye’s lens, which effectively filters out most UV light, protecting delicate photoreceptor cells.
Animals capable of UV vision often have specialized adaptations. Many possess photoreceptors, or cone cells, sensitive to UV wavelengths. Unlike humans, some animals also have lenses that do not filter UV light, allowing these wavelengths to reach their retinas. This enables them to perceive a broader spectrum, revealing details and patterns unseen by humans.
A World of UV Viewers
Many animals across various taxa are known to perceive ultraviolet light.
Insects like bees and butterflies are prominent examples, using UV vision for navigation and resource location. Ants, flies, spiders, and some dragonflies also possess this ability.
Many bird species, especially diurnal ones, see UV light, including songbirds, parrots, gulls, and raptors like American kestrels and rough-legged hawks.
Fish such as goldfish, carp, Japanese dace, trout, and salmon show UV sensitivity. Some, like damselfish, use UV patterns to distinguish individuals.
Many reptiles exhibit UV vision, including lizards like green iguanas, common wall lizards, and chameleons. Certain snakes also possess this ability.
Some mammals, though less common, perceive UV light. This group includes rodents (mice, rats, gerbils, voles), bats, hedgehogs, dogs, cats, ferrets, and reindeer.
The Advantages of UV Perception
UV perception offers significant ecological and behavioral advantages.
Foraging animals often rely on UV cues to locate food. Many flowers display intricate UV patterns (nectar guides) that direct pollinators like bees to pollen and nectar. Birds use UV vision to differentiate ripe fruits and berries, which appear more distinct than foliage. Some birds use UV to detect camouflaged insect prey; reindeer find lichen, a primary food source, which reflects UV.
UV vision plays a crucial role in mating and communication. Birds use UV patterns on their plumage for mate selection and species identification; some species appear distinctly different under UV light to avian eyes. Fish and reptiles employ UV-reflective scales or skin patterns, like iguanid lizard dewlaps, to signal mates or rivals.
UV vision also aids in navigation. Insects like bees and ants detect patterns in polarized UV light, using it as a “sun compass” for orientation during flights and migrations, even on overcast days. This helps them maintain a consistent direction.
UV vision also impacts predator and prey interactions. Prey camouflaged in visible light may stand out in UV, making them easier for predators to detect. Raptors like kestrels spot UV-reflective urine trails of small mammals like voles, tracking prey efficiently. Reindeer use UV vision to locate polar bears, which, despite blending into snowy landscapes in visible light, appear more discernible in UV.