The platypus is one of the planet’s strangest creatures on several counts. Though mammals, these Australian natives lay eggs and sport venomous spines on their rear legs. They also have beaver-like tails and duck-like bills, the latter of which they use to sense prey while hunting at night with their eyes closed.
Now, scientists have found yet another odd trait to add to the list: Fluorescent fur.
In a recent study published in the journal Mammalia, scientists found that when illuminated by ultraviolet (UV) light—a spectrum of light not visible to human eyes—the pelts of platypuses give off a blue-green glow.
“I was a little flabbergasted to [see] the platypus is biofluorescent,” says study lead author Paula Anich—especially since it’s already “such a unique animal.”
The finding expands science’s knowledge of biofluorescence, which researchers are finding to be more widespread throughout the animal kingdom than previously thought.
“This adds another observation that many animals are biofluorescent, and it opens up questions about what it might mean, if anything, for the species,” says David Gruber, a National Geographic explorer and researcher who studies fluorescence in marine creatures and who wasn’t involved in the paper.
From flying squirrels to platypus
Biofluorescence is the phenomenon whereby a substance, such as fur, absorbs light at one wavelength and emits it at a different wavelength. Common biofluorescent hues include green, red, orange, and blue.
In just the past few years, scientists have discovered that several types of sea turtle shells, fungi, and flying squirrels are biofluorescent. Though the reasons are unknown, hypotheses include camouflage or communication between individuals of the same species.
In 2019, Anich—a mammalogist at Northland College in Ashland, Wisconsin—and her colleagues found that flying squirrels fluoresce under UV light, emitting a pink glow from fur on their bellies. (Learn more about fluorescent flying squirrels.)
These studies led the team to Chicago’s Field Museum, where the researchers illuminated preserved squirrel pelts with UV lights. Out of curiosity, they did the same to a platypus specimen stored there—and saw the glow.
Shortly before Anich’s study was published, another research paper reported the finding that a freshly killed platypus on a road in Australia glowed under a black light, a lamp that radiates UV light.
That validates Anich’s finding and shows that living platypuses, not just long-dead ones, are almost certainly fluorescent, says Gilad Bino, a platypus expert at the University of New South Wales in Sydney, Australia.
“The platypus never ceases to amaze me,” says Bino of the new paper, with which he wasn’t involved.
To what end?
It’s still unclear why platypuses glow.
Since the animals are nocturnal and keep their eyes closed when swimming, it seems unlikely to serve an important role in communication with other platypuses, Anich says.
It may help them avoid certain predators that can see UV light; absorbing UV and emitting blue-green light could serve as a form of camouflage, Anich says.
Bino agrees that’s plausible. Many animals, including most birds, can see in UV. The platypus’s native predators include big fish such as Murray cod, birds of prey and dingos.
It’s also possible the trait has no real function—that it’s merely an ancestral trait that the platypus has retained in addition to its other primitive characteristics, such as egg-laying.
Both Anich and Bino say they hope to study a living platypus to confirm the biofluorescence discovery and perhaps learn more about the trait’s function.
“Given these findings,” Bino says, “you can be sure I’m getting a UV spotlight when I’m next in the field.”