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Do platypuses glow under UV light?
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Platypus (Ornithorhynchus anatinus)
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Platypus (Ornithorhynchus anatinus)
Platypus (Ornithorhynchus anatinus) Under ultraviolet light the fur of this semiaquatic, egg-laying Australian mammal emits a bluish green fluorescent glow.

Do platypuses glow under UV light?

Written by
Manjishtha Bhattacharyya
Manjishtha Bhattacharyya is an editor at Encyclopaedia Britannica. She holds a PhD in zoology from Vidyasagar University, West Bengal, and has more than seven years of experience in science communication...
Manjishtha Bhattacharyya
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Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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They do, and they are not the only mammals that show this trait. Biofluorescence—in which an animal absorbs light of one wavelength and then emits it at a longer wavelength, glowing in the process—was already known to occur in opossums, which are marsupials, and flying squirrels, which are placental mammals. Platypuses, however, were the first egg-laying mammals (monotremes) known to show this trait when their fur was found to glow under ultraviolet (UV) light.

In a study published in 2020, American researchers reported that the fur of platypus specimens kept in museums glowed bluish green when exposed to UV light. The specimens absorbed UV light with wavelengths between 200 and 400 nm (invisible to the human eye) and emitted light at wavelengths between 500 and 600 nm; the emitted light was visible as a bluish green glow against a dark background. About the same time, an independent study from Australia reported the phenomenon in a platypus that had died in a vehicle collision, providing evidence that the biofluorescence was not simply a feature of long-dead museum specimens. Both male and female museum specimens showed the trait, suggesting that it was not related to sex or reproduction.

Biofluorescence vs. bioluminescence

Although both processes involve light emission by organisms, they differ in their nature and mechanism of light production. Biofluorescence is not a chemical process. A biofluorescent animal absorbs light of a shorter wavelength, such as UV light, and emits it at a longer wavelength that is visible to the human eye under UV light (black light). Bioluminescence, on the other hand, involves a chemical reaction between the light-emitting molecule luciferin and the enzyme luciferase, which produces light. The glow of a firefly is caused by bioluminescence, whereas the light emitted by some corals, crystal jellies, and platypuses is the result of biofluorescence.

Biofluorescence has since been reported in more mammals, including the monotreme echidna and the marsupial wombat. Its occurrence across several mammalian species has led experts to suspect that it may be an ancestral trait in mammals.

But what purpose does biofluorescence serve in platypuses? Researchers do not have a clear answer yet. They suspect that it may help these animals, which are active during twilight and at night, avoid detection by predators. By absorbing some of the UV radiation, platypuses and other biofluorescent mammals may be able to camouflage themselves from predators that can sense UV light. Biofluorescence may also help individual platypuses find and communicate with one another, although this has not yet been conclusively proved.

Manjishtha Bhattacharyya