Platypuses are already one of nature’s strangest mammals: they lay eggs, have duck-like bills, webbed feet, venomous spurs, and hunt by sensing tiny electrical signals in the water. But researchers have found another surprising trait to add to the list: under ultraviolet light, platypus fur glows blue-green.

This phenomenon is called biofluorescence. It happens when a surface absorbs light at one wavelength and re-emits it at another, often making colors appear to glow in the dark under UV illumination. In ordinary daylight, a platypus looks brown. Under UV light, however, parts of its coat can shine with a cool teal or blue-green glow.

Scientists reported this after examining preserved platypus specimens in museum collections. When the animals were exposed to ultraviolet light, their fur fluoresced. The discovery was unexpected, though not entirely alone in the mammal world. Some other mammals, including flying squirrels, certain marsupials, and even some monotremes’ relatives, have also shown fluorescent qualities.

Why platypuses glow is still uncertain. It may not have a clear purpose at all; sometimes fluorescence is simply a byproduct of chemicals in fur, skin, or other tissues. Another possibility is that it plays a subtle role in camouflage or communication. Because platypuses are mostly nocturnal or crepuscular, active around dusk and night, UV-related effects might matter more in low-light environments than we realize.

The find is a reminder that even familiar animals can hold hidden features, especially when viewed with different tools. Ultraviolet light reveals details our eyes normally miss, turning a muddy-brown river mammal into something that looks almost magical.

For the platypus, glowing blue-green under UV light is not its only oddity, but it perfectly fits its reputation: a creature that seems assembled from surprises. It also shows how much remains to discover, even in animals scientists have studied for generations.