Do Platypuses Glow Under UV Light?

The platypus (Ornithorhynchus anatinus) is one of the strangest animals on Earth. A monotreme—an egg-laying mammal—it possesses traits rarely found together: a flattened bill used for sensing prey underwater, webbed limbs adapted for swimming, and venomous spurs in males, used for defense. Females are born with small vestigial spurs that disappear before they are a year old. In 2020 scientists discovered something even stranger: the platypus glows under ultraviolet (UV) light.

Researchers from Northland College in Ashland, Wisconsin, and Colorado State University in Fort Collins found that, when three preserved platypus specimens from Tasmania and New South Wales, Australia, were exposed to UV light, their fur emitted a blue-green fluorescent glow. This glow, called biofluorescence, occurs when an organism absorbs higher-energy (shorter-wavelength) light—such as UV light—and then emits lower-energy (longer-wavelength) light that is visible to human eyes. It is different from bioluminescence, which occurs when light is generated by a chemical reaction inside an organism, such as fireflies or certain jellyfish. Biofluorescence is not unique to platypuses. The phenomenon had been observed in such mammals as opossums and flying squirrels, and it has since been documented in spring hares, wombats, and other species.

So, why does a platypus glow? No one knows for sure. One idea is that the absorption of ultraviolet light that precedes the glow may help with camouflage, by making the platypus less visible to predators that can see UV light. Another possibility is that fluorescence helps platypuses recognize one another at night. But it may just be a chemical property of the animal’s fur, with no special purpose at all. It is worth noting that the first glowing platypuses scientists studied were museum specimens, not living animals. That means the chemicals in their fur might have changed slightly over time. However, examination of fresh remains has suggested that living platypuses glow, too.