Platypuses glow a vibrant bluish-green under ultraviolet light.

In a study published in the journal Mammalia in October 2020, researchers from Northland College in Wisconsin discovered that platypuses are biofluorescent. Led by biologist Paula Spaeth Anich, the team examined preserved specimens from the Field Museum of Natural History in Chicago and the University of Nebraska State Museum. Under ultraviolet light, the seemingly dull brown fur of both male and female platypuses emitted a distinct blue-green glow.Biofluorescence occurs when a substance absorbs high-energy light, such as UV radiation, and re-emits it at a lower energy level as visible color. This is different from bioluminescence, where an organism produces its own light through chemical reactions. The researchers found that the platypus fur absorbs UV wavelengths between 200 and 400 nanometers and re-emits visible light between 500 and 600 nanometers. This makes the platypus one of the few known mammals to exhibit this trait, alongside opossums and flying squirrels.Scientists believe this adaptation is linked to the platypus's crepuscular and nocturnal lifestyle. Since they are active at dawn, dusk, and during the night, biofluorescence may help them navigate low-light environments or interact with other platypuses. It might also serve as a form of camouflage called disruptive coloration to avoid predators that can see UV light. This discovery suggests that biofluorescence in mammals may be more common and evolutionarily ancient than previously thought.