It turns out that glowing under UV light is surprisingly common for mammals – in fact, a new study shows that it’s weird not to glow under ultraviolet light.
There have been reports over the past few years about mammals like squirrels and platypuses fluorescing under UV – and if you’ve ever been in a room with a UV light like a disco, you’ll know that human teeth and nails fluoresce too.
“We knew about maybe less than 50 species,” says Dr Kenny Travouillon, curator of mammalogy at the Western Australian Museum, and lead author on a paper published in Royal Society Open Science.
“We’ve more than doubled that as a result of this study.”
Travouillon and colleagues have identified 125 different species of mammal that fluoresce under UV.
“Our aim was to try and basically cover the mammal family tree as much as possible to see if it was common or not,” he says.
“We managed to get every order of mammal, so that’s 27 orders, and 79 families, which is the vast majority of families – but not all of them.”
The researchers used preserved specimens at the Western Australian Museum collection to figure out which ones fluoresced – that is, they absorb ultraviolet light, and reflect it back as visible light.
“After five minutes of shining light on things, we were like ‘oh, that’s glowing, that’s glowing, that’s glowing,” says Travouillon.
After some initial discoveries with a torch, they teamed up with Curtin University researchers to test samples with a spectrophotometer to precisely measure the exact wavelengths of light absorbed and reflected.
“We found that actually, it was everywhere in the family tree, but it will be different parts of the animal that fluorescence. The most common was the fur – it was white to light fur that was fluorescent.
“In some of them, it was the skin that was fluorescent, like in bilby ears. And sometimes it was the nails or just the teeth.”
Animals with more pigment tended to glow less, but they all glowed.
“The one that had the least amounts that we got was the dwarf spinner dolphin, because the skin is really, really pigmented so it’s really dark,” says Travouillon.
“So that part didn’t fluoresce at all, but its teeth did.”
So why does all this glowing happen?
“We can only speculate – I think it will be case-by-case,” says Travouillon.
But for hair and fur, the researchers think UV fluorescence might be the default.
“It’s been shown in many studies that human hair, when it turns white and loses all the pigmentation, it glows under UV lights,” says Travouillon.
“It’s the pigmentation that masks the fluorescence – so the darker it is, the less fluorescent it will be. It’s the same thing with nails. If you have nails that are very white, they will be fluorescent. But a lot of species have black nails.”
They also found that the way a specimen had been preserved affected how much it glowed. The first platypus in the museum collection glowed differently to the ones reported by US researchers.
“We decided we would test that properly by doing it on a frozen platypus that’s freshly dead, as well as the same animal after it’s been prepared with borax, and also compare that to the specimens that were older in our collection that were prepared with arsenic,” says Travouillon.
“We found a difference between all three. The platypus that had not been preserved was the least fluorescent – it still had fluorescence, but it was very mild – and then after preparing it with borax, that fluorescence was intensified, and arsenic had the most. So we think here preservation does impact the fluorescence, but it’s only the intensity, not the ability to fluoresce.
“When we looked at the Tasmanian devil or the koala, it’s the opposite. The frozen ones were very, very bright. After they’d been preserved, the intensity actually lowered,” says Travouillon.
Do you have a UV torch lying around (maybe off a rapid antigen test?) Travouilllon says it’s fine for people to see if their cat or dog glows too – with one condition.
“They need to make sure that they don’t shine the light in the eyes of their pets, because UV lights can be damaging to the eyes,” he says.
“But if they put a bit of light on their fur, or their nails, just to have a bit of fun, it’s totally fine. It will be a bit of fun to do with families.”