SCULLY: The National Weather Service last night reported atmospheric conditions in this area that were possibly conducive to lightning.

MULDER: Possibly.

SCULLY: It is feasible that the truck was struck by lightning, creating the electrical failure.

MULDER: It’s feasible.

SCULLY: And you know, there’s a marsh over there. The lights the driver saw may have been swamp gas.

MULDER: Swamp gas?

Back in the day, swamp gas was one of the go-to explanations for UFO sightings. As a youngster watching X-Files, I had no idea that swamp gas might be liable for another sighting of the night, one that dominates the zeitgeist for a certain portion of the year.

As it turns out, swamp gas might be responsible for this:

An image of a jack-o-lantern, a pumpkin carved with a toothy grin and eyes, glowing from candlelight
A jack-o'-lantern - photo by Toby Ord

To explain the link, we need to back up to the days of ancient humanity.

In the time before electricity, nights were a completely different beast. When the sun sank below the horizon, humans relied on candlelight or lanterns. Indoors, this method of illumination was poor enough, but outside it was a nightmare. As it might be easy to imagine, most people refrained from traveling into the abyss of nighttime. The obverse of this coin is a significant reduction in light pollution. When one stepped outside at night, if something emitted photons, one could see it with a clarity we can only fantasize about today.

In olden days, a phenomenon often tormented the traveler of the night. When moving through swamps, bogs, or marshes, humans might be confronted by an “atmospheric ghost light.” To the people at the time, they were ghosts, fairies, or spirits of some sort. These entities floated around, emitting brightness despite the lack of sunlight.

They called these geists will-o’-the-wisp.

The Will o' the Wisp and the Snake by Hermann Hendrich

Unsurprisingly, in Britain and Ireland, where they have a lot of bogs, the will-o’-the-wisp acquired a number of folktales to explain the phenomenon.

One version sees a sinful blacksmith named Will die, after which he goes to the pearly gates. There, St. Peter offers him a second chance at life to atone for his wrongdoings. Instead, he continues his wicked life and is sentenced to wander the earth as punishment. The Devil shows up to give him a single burning coal to warm himself. Will employs the ember to draw mortals into the marshes at night.

In an Irish rendition, the protagonist’s name is changed to Jack. His evil ways lead to the Devil coming to take his soul. Jack asks the Devil to turn himself into a coin, so he can buy one last drink before going to the underworld. The Devil agrees, but Jack puts the coin in his wallet, which conveniently has a crucifix inside it. Proximity to the cross disables the Devil’s ability to return to normal form, trapping him in the wallet. The Devil offers Jack a decade of life if he will allow him to escape. After 10 years, the Devil returns, ready to take Jack to Hell. In another ruse, Jack asks the Devil if he could have one apple to tide over his hunger for the journey below. The Devil climbs a tree to pick the fruit, but Jack carves a crucifix in the trunk, which traps the Devil. To find freedom this time, the demon must consent never to take Jack to Hell. Seems a great bargain for Jack. However, he’s a bad person, so he can never go to Heaven. When he died, he was rejected at the Gates of Heaven. Jack travels to Hell, looking for a place to reside for eternity. The Devil, honoring his deal, sends Jack back to Earth to roam as a ghost. To lighten his load, he grants him a burning ember, which Jack places in a hollow turnip to use as a lantern.

An 1862 oil painting of a will-o'-the-wisp by Arnold Böcklin

The term will-o’-the-wisp comes from this tale about Will. A “wisp” was a bundle of sticks sometimes used as a torch in the night. Hence, Will was Will of the Torch. The ghostly light one might encounter in the night was the ghost of Will.

As you might have gathered already, a jack-o’-lantern was a will-o’-the-wisp! Jack of the Lantern. What we today call carved pumpkins were originally hollowed turnips with candles inside that represented the spirit of Jack roaming the realm between Heaven and Hell.

Other fantastic names for the light phenomenon included “friar’s lantern,” “hinkypunk,” “spook-lights,” “corpse candles,” and “fairy fire.” A Latin phrase – ignis fatuus – combines the words for “fire” and “foolish.” These lights were said to lure the foolish to their swampy doom through the fiery lights. Still, will-o’-the-wisp was the most common sobriquet in the British Isles.

People inhabiting all continents seemed to encounter the will-o’-the-wisp, though the naming conventions varied.

Instead of dismissing the sightings as fairy tales, scientists over the centuries have taken for granted that people witness lights in marshes.

But what causes the phenomenon?  Various theories exist. 

One obvious cause might be fireflies. The bioluminescent insects certainly light up the night sky. However, most people are familiar with fireflies and would be unlikely to mistake them for ghosts. Other bioluminescent and chemiluminescent entities like to inhabit bogs, however. Certain fungi glow, creating a reaction sometimes called foxfire. Some commentators have suggested that fireflies or glowing fungi might not necessarily be the moving wisps, but they could produce the light that is reflected off of nocturnal avians, such as white barn owls.

Panelluses stipticus producing foxfire - photo by Ylem

Another idea is the cold flame. Despite the light, a will-o’-the-wisp is said to be cool. A cold flame is a bluish halo that transpires in some compounds when they reach temperatures just below their ignition point, which produces little heat. These reactions happen frequently in hydrocarbons, which just happen to occur abundantly in decayed organic material in swamps.

This notion leads us back to the most common explanation: swamp gas.

Cue Dr. Scully: “It’s a natural phenomenon in which phosphine and methane rising from decaying organic matter ignite, creating globes of blue flame.” In the show, Mulder responds, “Happens to me when I eat Dodger Dogs.”

The swamp gas theory hinges on the cycle of life and decay in a swamp. Organic matter decomposes in the wet environment. The new constituents that arise are phosphine, diphosphane, and methane. When the first two rise from the water and contact with oxygen, they spontaneously ignite, which in turn might burn the methane. The result would be an ephemeral fire in the middle of a fen.

So, the next time you carve a pumpkin and shove a candle inside, remember that your tradition likely evolved from swamp gas.

Or Dodger Dogs.

This fascinating examination of the origins of glowing pumpkins must end on a bit of a downer. Sightings of the will-o’-the-wisp – the natural version – have significantly dropped in the recent past. The reason has nothing to do with the enlightenment of modern humans or light pollution. Instead, we’ve drained many of the world’s swamps for farmland, habitation, or cities. Without swamps, there is no swamp gas. Without swamp gas, there is no will-o’-the-wisp. A point to the swamp gas theory, to be sure, but a point against the natural biomes of the planet.

Where will Will and Jack roam without the marshes? They might need to divert themselves to Dodger Stadium for the required fuel.

Post-script: Yet another item to add to the Magic: the Gathering encyclopedia!

Further Reading and Exploration

Will-o’-the-Wisp/Jack-o’-Lantern – University of Pittsburgh

Natural Wonders: Will-o’-the-Wisp – ExplorersWeb

How Jack O’Lanterns Originated in Irish Myth – History

The spirit of biodiversity – The Paleontology Newsletter

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