Quick Take
- Flying squirrels glow a vivid, unexpected color under UV light, a phenomenon that scientists still can't agree on why it occurs. See the 2019 study →
- Biofluorescence and bioluminescence sound alike but work completely differently, with only one of them requiring you to bring your own light. Explore the science difference →
- These squirrels are nocturnal gliders with a secret social life that makes their UV glow even more puzzling. Discover their secret social life →
- More animals fluoresce under UV light than you'd ever expect, and some of the species on the list will genuinely surprise you. Watch glowing animals →
Some animals can produce a pretty dramatic glow under ultraviolet light, but the phenomenon is a little different from simply “glowing in the dark.” Biofluorescence happens when an animal absorbs shorter-wavelength light, such as ultraviolet light, and re-emits some of that energy as visible light. Scientists have now documented the effect in a surprisingly wide range of animals, including budgerigars, flying squirrels, springhares, and wombats. Even parts of Atlantic puffin bills and the feathers of some owls can fluoresce under UV light. Take a look at what happens when these animals are viewed under a black light.
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How Do Animals Glow in the Dark?
Animals may glow in the dark to find a mate or for communication.
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Biofluorescence requires an outside light source. Molecules in an animal’s feathers, fur, skin, shell, or other tissues absorb higher-energy wavelengths and release some of that energy at longer wavelengths that humans can see. Depending on the species and the compounds involved, the result may appear green, blue, pink, red, or another color. That is different from bioluminescence, in which an organism produces light through a chemical reaction of its own. Researchers have identified fluorescent pigments and compounds in some animals, including porphyrins, but there is no single mechanism responsible for every fluorescent species.
What the fluorescence actually does is another question. In some species it may play a role in signaling, while researchers have proposed camouflage or other functions for certain animals. In plenty of cases, scientists simply do not know whether it provides an evolutionary advantage at all. A 2019 study documented vivid pink fluorescence in all three living species of New World flying squirrel: Glaucomys oregonensis, Glaucomys sabrinus, and Glaucomys volans. Researchers found the effect in males and females, museum specimens, and living animals, but its ecological purpose remains unclear.
Where Do New World Flying Squirrels Normally Live?
So, where could you actually encounter a fluorescent flying squirrel? One of the three species in the study was Glaucomys volans, better known as the southern flying squirrel. Its range covers much of eastern North America, reaching west toward the prairie tree line and south to the Gulf Coast. Populations also occur in Mexico and Central America as far south as Honduras, while its Canadian range includes parts of Ontario, Quebec, and Nova Scotia.
Southern flying squirrels are forest animals, and good habitat usually includes mature trees that provide both food and nesting cavities. Hardwood forests with mast-producing trees are particularly useful because nuts and seeds make up part of their diet. The squirrels do not normally excavate their own tree cavities. Instead, they often use natural hollows or existing holes, including cavities originally made by woodpeckers. Despite the name, flying squirrels do not truly fly. A membrane of skin between their limbs allows them to glide from tree to tree.
How Do Flying Squirrels Normally Behave?
Southern flying squirrels are nocturnal, which means most of their activity happens after sunset. They spend much of that time moving through trees, gliding between trunks, and searching for food. Their ability to operate in darkness is one reason researchers have been interested in the fluorescence discovery. The original study noted that all three Glaucomys species are nocturnal or active around twilight, but scientists have not established that fluorescence helps them see one another or serves any other particular nighttime function.
They are also more social than their nighttime lifestyle might suggest. Southern flying squirrels can share nest cavities, with communal nesting particularly useful during cold weather because several animals can conserve heat together. Researchers have also recorded both southern and northern flying squirrels producing high-frequency and ultrasonic vocalizations. Those calls appear capable of carrying information between squirrels, but scientists are still working out exactly what the different sounds mean. So while the pink UV glow is impressive, there is still quite a bit about these little nighttime gliders that we do not fully understand.
