It’s Easy Being Green: Most Amphibians Are Biofluorescent, Study Finds

An alpine newt glows green after being exposed to blue light.
An alpine newt glows green after being exposed to blue light.
Jennifer Y. Lamb and Matthew P. Davis

If you walk through a forest at night, you see only darkness and shadows, and perhaps the smudgy outline of trees against the sky. But if you were a salamander snuggled in the leaf litter, under the right light conditions, you might see something completely different: foliage glimmering in shades of red, and your fellow amphibians glowing in brilliant greens.

Biofluorescence—in which animals emit a fluorescent glow after absorbing high-energy wavelengths of light—is likely widespread among most, if not all, amphibians, according to a new study published in the journal Scientific Reports. Previously, only one species of salamander and three frog species were known to biofluoresce.

Alpine newt under white light
The same view of an alpine newt under white light
Jennifer Y. Lamb and Matthew P. Davis

“I do field work, so I’m out there capturing species of amphibians, and I think, ‘huh, I wonder if this fluoresces,’” says Jennifer Y. Lamb, an assistant professor of biology at St. Cloud State University in Minnesota. She and co-author Matthew P. Davis, an assistant professor at the university, collected representatives from eight of the 10 salamander families, five families of frogs, and one family of caecelians, a type of limbless amphibian. They exposed each critter to high-energy blue light and then viewed them through a yellow filter to see if and how they glowed.

“One of the first salamanders we tested was the Eastern tiger salamander. We saw that it fluoresced really brightly, and that kind of got us hooked,” Lamb tells Mental Floss. “We started [to look] across salamander diversity, [and asked ourselves], ‘OK, how many species do we see within salamanders that biofluoresce?’ When we started to notice, ‘hey, it’s actually a lot of them!’, the question became, ‘can frogs do it?’ Then we looked at a relative of frogs, the caecelians—‘do they do it?’ And it seemed like biofluorescence in some form or fashion is present in all of these lineages.”

Biofluorescent salamander
A biofluorescent Eastern tiger salamander
Jennifer Y. Lamb and Matthew P. Davis

The various amphibians fluoresced in unique patterns depending on their skin’s coloration and markings as seen under normal white light. Some gleamed in blotches, others in stripes. A few animals' bones glowed. Lamb was surprised to see that salamanders’ bellies, which were usually red or orange under white light, glowed brighter than their backs after exposure to blue light.

“A lot of these newts have evolved what we call aposematic coloration, or warning colors. When they’re threatened by a predator, they’ll basically contort their bodies to show off their bellies as a warning,” Lamb says. “So it begs the question, if these bellies are also biofluorescent, then maybe some of their predators can visualize biofluorescence.”

The researchers intend their study to be a roadmap for further study into the fascinating ability. “Now that we know that this phenomenon exists across amphibians, there’s all kinds of interesting applications that future researchers may head towards,” Davis tells Mental Floss. For example, no one yet knows what kind of mechanisms allow amphibians to biofluoresce: In some groups it might be a color-based molecule or compound; in others, maybe something in their mucus.

Biofluorescent frog
A Cranwell's frog glows under blue light.
Jennifer Y. Lamb and Matthew P. Davis

Scientists also don’t know exactly how different amphibians might visualize their own biofluorescence. Salamanders, frogs, and caecelians have rod cells in their eyes that are sensitive to green light, suggesting that they may have evolved green biofluorescence and the ability to see it at the same time, though further research is needed on that front.

“We have to be careful about not falling into the trap of only perceiving the world through our own eyes,” Lamb says. “Human vision is set to a particular set of wavelengths, and that’s not the case across all animal diversity. And that may not be the case in terms of these amphibians.”

Biofluorescent salamander
A biofluorescent three-lined salamander
Jennifer Y. Lamb and Matthew P. Davis

Finally, researchers are debating what purpose biofluorescence serves. In other animals, scientists have suggested it could play a role in communication, camouflage, or choosing a mate. Amphibians might use biofluorescence to locate each other in dense leaf litter.

“We’re hoping this study stimulates researchers to start looking at biofluorescence more broadly across the various different kinds of amphibian lineages that they may work on, so we can fill in the gaps in knowledge,” Davis says.

“There’s still a lot to learn about animal groups that we think we know,” he adds. “There’s still lots of interesting things out there to find that can help us rethink their life history and biology, and that may point us in new exploratory directions.”

Beyond Tiger King: 10 Fascinating Animal Documentaries You Can Stream Right Now

A scene from Catwalk: Tales from the Cat Show Circuit (2018).
A scene from Catwalk: Tales from the Cat Show Circuit (2018).
Markham Street Films

By now, you've probably already binged Netflix's bewilderingly bonkers docuseries Tiger King (2020). If you're ready to dive deeper into the animal kingdom, there are plenty more documentaries out there. From wildcats to whales, these 10 films will take you on a cinematic adventure around the world, introducing you to captivating creatures and the people who love them.

1. The Tigers of Scotland (2017)

The Tigers of Scotland (2017) brings viewers as up close and personal as possible with a small but mighty feline: the Scottish wildcat. The film delves into the efforts to conserve the disappearing Highland tiger, as well as the history and mythology surrounding the UK’s only “big cat.”

Watch it: Netflix, Amazon, iTunes

2. Ghost of The Mountains (2017)

This 2017 Disneynature documentary will transport you to the world’s highest plateau in search of a family of snow leopards. These cats are famously tough to find, so Ghost of the Mountains offers viewers behind-the-scenes footage of what it’s like to track the elusive beasts.

Watch it: Netflix, Google Play, Youtube

3. Catwalk: Tales from the Cat Show Circuit (2018)

This delightful documentary takes you deep into the competitive cat show circuit. Both charming and at times cutthroat, the film brings viewers on a journey to see which of the many cool cats and kittens will be crowned Canada's top cat.

Watch it: Netflix

4. Kingdom of the White Wolf (2019)

Follow along as a National Geographic explorer and photographer embeds with a white wolf pack in the high Arctic. These wild wolves aren't used to seeing people, giving the filmmakers—and audience—an intimate window into the pack's daily lives and familial bonds. In addition to showcasing captivating footage of the animals, the three-part docuseries also features sweeping views of the starkly beautiful Ellesmere Island.

Watch it: Disney+, YouTube TV

5. Dogs (2018)

This docuseries, which highlights various dogs and their humans from around the world, celebrates the bond between people and their pups. But it’s more than just a montage of feel-good moments about humankind’s best friend: Each episode tells a broader tale about the human condition, crafting an emotional narrative that pulls at the heartstrings like a puppy tugging on a toy.

Watch it: Netflix

6. Dancing with the Birds (2019)

These birds will put your dad moves to shame. Watch the male avian performers shimmy, shake, and flash their feathers while attempting to woo their female mates. The documentary, narrated by Stephen Fry, offers a colorful look at the wonderfully wacky world of bird mating rituals.

Watch it: Netflix

7. Honeyland (2019)

This documentary follows Hatidze Muratova, one of the last wild beekeepers in a remote village in North Macedonia. She lives with her ailing mother, nurturing a traditional way of beekeeping passed down through the generations and striking a balance between making a living and maintaining ecological balance. But everything changes when a nomadic family settles nearby, threatening Muratova’s way of life. The resulting story is both sweet and stinging.

Watch it: Hulu, Amazon Prime, YouTube, Google Play

8. Virunga (2014)

This 2014 documentary highlights the park rangers fighting to protect the Congo’s Virunga National Park, home to the critically endangered mountain gorilla. As poaching and oil exploration threaten the park, the rangers and conservationists risk their lives to guard the rare creatures that inhabit it.

Watch it: Netflix

9. Harry & Snowman (2016)

In the 1950s, Harry deLayer bought Snowman, a run-down plow horse destined for slaughter, for just $80 at an auction. Within months, the two were taking the show jumping circuit by storm, launching both horse and rider to new heights. This documentary tells the story of the friendship the two developed, and chronicles their lives both in and out of the competitive spotlight.

Watch it: Amazon Prime

10. The Whale and the Raven (2019)

The waters around Canada’s Great Bear Rainforest are a haven for whales, who feed and find refuge in the quiet channels. With stunning visuals, this documentary highlights the tension of a community’s push to protect its wild places against the pressures of the ever-encroaching natural gas industry.

Watch it: Amazon Prime

Why Cats Like to Shove Their Butts in Your Face, According to an Animal Behavior Expert

This cat might be happier showing off its butt.
This cat might be happier showing off its butt.
Okssi68/iStock via Getty Images

Cats are full of eccentric behaviors. They hate getting wet. Their tongues sometimes get stuck midway out of their mouths, known as a “blep.” And they’re really happy hanging out in bodegas.

Some of these traits can be explained while others are more mysterious. Case in point: when they stick their rear end in your face for no apparent reason.

Are cats doing this just to humiliate their hapless caregivers? What would possess a cat to greet a person with its butt? Why subject the person who gives you food and shelter to such degradation?

To find out, Inverse spoke with Mikel Delgado, a postdoctoral fellow at the School of Veterinary Medicine at UC Davis. According to Delgado, cats don’t necessarily perceive their rectal flaunting as anything aggressive or domineering. In fact, it might be a cat’s way of saying hello.

“For cats, it’s normal for them to sniff each other’s butts as a way to say hello or confirm another cat’s identity,” Delgado said. “It’s hard for us to relate to, but for them, smell is much more important to cats and how they recognize each other than vision is. So cats may be ‘inviting’ us to check them out, or just giving us a friendly hello.”

For a cat, presenting or inspecting a butt is a kind of fingerprint scan. It’s a biological measure of security.

Other experts agree with this assessment, explaining that cats use their rear end to express friendliness or affection. Raising their tail so you can take a whiff is a sign of trust. If they keep their tail down, it’s possible they might be feeling a little shy.

If you think this situation is eased by the fact you rarely hear cats fart, we have bad news. They do. Because they don’t often gulp air while eating, they just don’t have enough air in their digestive tract to make an audible noise. Rest assured that, statistically speaking, there will be times a cat giving you a friendly greeting is also stealthily farting in your face.

[h/t Inverse]

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