Tiny bioluminescent animals called copepods recently lit up the snow near a remote field station, in the first documented sighting of its kind.

High in the Russian Arctic, at a remote field station on the shores of the White Sea, biologist Vera Emelianenko set out for a walk on a frigid December night. With her were Mikhail Neretin, the son of the station’s molecular biologist, and a couple dogs: a giant schnauzer and soft-coated Wheaten terrier.

Trudging along the icy embankments of the tidal zone in fierce Arctic winds, Neretin spotted a blue illumination in a snowbank. Had Emelianenko dropped her phone?

As they walked over to investigate, their footsteps created streaks of ethereal blue. “They were like blue Christmas lights in the snow,” Emelianenko says.

She bent down to scoop up a handful. With a gentle squeeze, the snowball glowed brighter. The dogs left a glowing trail as they raced ahead, as though the Northern Lights had seeped from sky to snow.

After a flurry of phone calls and texted photographs, the station’s biologists and a group of marine scientists across Russia were buzzing over the find. Emelianenko and Neretin took the station photographer, Alexander Semenov, out to document the lights. “We stomped the ground all together for maybe two hours” to get the spots to shine, Semenov says.

The next day, Emelianenko slipped a glowing snowball under a stereo microscope to try to identify the bioluminescent culprit. As she waited for the ice to melt away, she prodded miniscule detritus with a needle to no avail. But then Emelianenko spotted some copepods, tiny aquatic crustaceans, in the slushy petri dish. When she poked them, they shone a faint blue.

This may be the first documented explanation for glowing snow in the Arctic, which has been observed occasionally by researchers over the years but not been rigorously tested.

 Copepods are miniscule crustaceans just a few millimeters long, about the size of several grains of sand in a row. “They’re the bugs of the sea,” explains Steven Haddock, a marine biologist studying deep-sea zooplankton at the Monterey Bay Aquarium Research Institute. “They’re small and numerous, they’re eaten by a lot of things.”

While they don’t exactly get a lot of press or cultural representation (with the notable exception of Plankton, a copepod in SpongeBob SquarePants), copepods make up the plurality of biomass in the ocean, according to some estimates. They’re passive swimmers, meaning they can’t resist the currents. This particular species of copepod—Metridia longa—is tossed around the oceans from Canada’s Hudson Strait to the waters of Maine and all across the Arctic.

Even so, Metridia have no business on the shores of the White Sea, says Ksenia Kosobokova, an expert on Arctic marine zooplankton at Russia’s Academy of Science in Moscow. They’re usually found farther out in the ocean, migrating to depths of 80 to 300 feet during the day and ascending to a few feet from the surface during the darkness of night (which, in the winter, is most of the time), Kosobokova explains.

What must have occurred, Kosobokova says, is that the copepods were caught in a powerful current. Twice a day when the White Sea’s rising tide sweeps ashore, the frigid water and everything in it is sluiced through cracks in the ice and snow. For weak swimmers like copepods, there’s no escape.

It could be that tides were particularly strong on the day of the first sighting, December 1—the moon was almost new and three days away from 2021’s closest perigee, the time when the moon is nearest to the earth. Both conditions make for stronger tides. But a second round of sightings on December 16 suggest that it may not take a once-in-a-year lunar cycle to create conditions for the glowing snow.

 Most bioluminescence is produced when a small energy-storing molecule called luciferin is oxidized. On its own, luciferin produces a very faint, steady glow. But combined with the enzyme luciferase, the reaction is sped up, and that glow becomes a dramatic burst.

“So we have these two molecules inside of them, a light emitter and an accelerator,” Haddock explains. For some copepods, the luciferin and luciferase react internally, but Metridia longa has glands on its head and body to secrete its incandescence into the world. “They’ll shoot out those two molecules at the same time and form a little puff of light in the water.” (Learn more: How bioluminescence works in nature.)

Scientists believe Metridia and other copepods use bioluminescence as a defense. “One idea is that the light could startle predators and cause them to spit out the copepod” or distract them long enough for the copepod to escape, says Todd Oakley, a professor of evolutionary ecology and marine biology at the University of California Santa Barbara.

Kosobokova figures the copepods nestled in the snow were fading but alive—after all, Arctic plankton are no strangers to freezing temperatures. But bioluminescence experts say they may well have been dead—making their blue glow somewhat ghostly. 

As many ham-handed children are sad to learn, fireflies still glow if you accidentally squish them.

“It happens for us with our scientific specimens,” Haddock adds. “You collect an organism and you put it in the freezer for later study. And then when you pull it out, it will slowly start to glow—the chemicals that are inside of their bodies are still perfectly capable of reacting.”

Emily Lau, a graduate student at UCSB, studies the biochemistry of bioluminescence in fishes and the copepod’s crustacean cousin the ostracod. They look like sesame seeds with eyeballs. “People can dry them, and then you can still crush them in the water after they’re dead and they will produce bioluminescence,” she explains.

“As long as that small molecule luciferin is present, then the bioluminescence is going to occur,” Lau says.

Jørgen Berge, a professor at the Arctic University of Norway who studies polar night and arctic marine ecosystems, says it may be too early to give copepods credit for the light show. Berge has observed similar deposits in the snow on the shores of the Norwegian archipelago Svalbard, which he believes are better explained by clumps of dinoflagellates, single-celled algae that also bioluminesce (although he hasn’t tested the spots to identify their composition.)

Dinoflagellates are behind many spectacular marine displays of bioluminescence—like the “phosphorescent bays” of Puerto Rico, where bathers can splash each other with light, or the dolphins that leave ethereal glowing trails off the coast of California. (Related: This deep-sea shark is one of the world’s largest glowing animals.)

“It’s very easy to direct your attention to the larger organisms [in a sample],” Berge explains. But identifying a creature capable of bioluminescence in the sample doesn’t mean another, less obvious creature isn’t responsible. However, Berge agrees that the lights are particularly bright, even for dinoflagellates.

Perhaps what’s most surprising is that glowing snow had not been seen before at a biological station that’s been active for over 80 years—only to be spotted by Emelianenko, 24, and Neretin, 18. That could be because most folks don’t go for leisurely December strolls in the Arctic night, Kosobokova says. It’s not very hospitable. “We also get bears and wolves up here,” Semenov adds.

But the young biologists’ keen eyes and tolerance for cold was rewarded. “There’s so many mysteries out there if you’re willing to have a childlike curiosity,” Haddock says.

Semenov agrees. “You never expect that there will be beauty right under your nose that you haven’t realized can exist.”

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