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‘Will-o-the-wisp and snake’ by Hermann Hendrich.

In the Spirit of Science: Casting Light on the Enchanting Will-o’-the-Wisp


Will-o’-the-Wisps, also called “ignis fatuus,” Latin for “foolish fire”, are enchanting balls of greenish-blue floating lights observed over swamps and marshes at night. At a distance, they look identical to flickering lanterns. All over the world, since ancient times, people have struggled to rationalize with the origins of these mystery lights; thus, legends and myths appear in almost every ancient culture surrounding Will-o’-the-Wisps.

Arnold Böcklin, oil painting, Will-o’-the-Wisp, 1882.

Arnold Böcklin, oil painting, Will-o’-the-Wisp, 1882. (Public Domain)

They make appearances in historical literature such as Shakespeare’s 16th century play  King Henry IV, the 17th century Paradise Lost by John Milton, and in the 19th century in Bram Stoker’s  Dracula, in which they were an omen to the impending horrors of Dracula’s castle. They also appear in today’s pop-culture in The Neverending Story, Lord of the Rings, and in Harry Potter. However, to understand the place of Will-o’-the-Wisps in mythology and to establish what they actually are, we must travel far back into time - but we will begin with the first written record of the phenomena.

Will-O’-the-Wisps / Jack-O’-Lantern

Will-o’-the-wisps appear in Europe’s written record around the 13th century and tell us that ancient Celtic cultures in Britain and Ireland gave them dozens of names, most famously: “Joan the Wad,” “Jack-o’-Lantern,” “Peg-a’-Lantern,” and “Jenny with the Lantern.” For the most part, Will-o’-the-Wisps were believed to spirits/souls in ‘limbo’ unable to enter either heaven or hell. Hanging around treacherous swamps, marshes, and cemeteries, these enchanting lights lured travelers off their paths and were also seen as omens of death. When they were seen in cemeteries it was held that the only way to clear a wisp was to throw a handful of dirt from “its” graveyard.

A traditional Irish Jack-o'-Lantern in the Museum of Country Life, Ireland.

A traditional Irish Jack-o'-Lantern in the Museum of Country Life, Ireland. (rannṗáirtí anaiṫnid/CC BY SA 3.0)

Ancient Norse cultures were the first to call Will-o’-the-Wisps Jack-o-Lanterns, and in the Netherlands the “Irrbloss,” “Iiekko,” and “Iygtemand” were said to be the "souls of un-Baptized children”, leading travelers to water for Baptism. They were also held to guard buried treasure which could only be found using “a dead man’s hand or after eating seeds from a magical fern.” In Denmark they were seen as homes of the “spirits of unrighteous men.” In German legends, Will-o’-the-Wisps tormented drunks on their way home and were often reported to have burned their feet when they had fallen over.

In ancient Asian texts the “aleya” and “chir batti” were seen hovering at places where people died, and in South America the phenomena was greatly feared, as it was believed to be a malevolent energy generated by an evil goddess. In ancient Mexico, they were the souls of witches and in ancient Argentina they were called “Luz Mala” (evil light). If the light was red it was maintained that Satan himself was tempting the onlooker and in aboriginal Australia, similarly, the lights were called “min min lights” and were reported as “following people who saw them.” If the traveler was silly enough to follow the light, they were walking in the hoof-steps of the devil and “were never seen again.”

A Japanese rendition of a Will-o’-the-wisp of Russia.

A Japanese rendition of a Will-o’-the-wisp of Russia. (Public Domain)

Even today in the United States, millions of online ghost hunters collect blurry photographs of “orbs” - balls of colored light believed to be souls. Furthermore, in the swamplands of Louisiana the phantom is widely known as “fifollet” representing the dark souls of folk who had been sent back from heaven to “serve more time” - to do penance on earth. It might be worth considering that the lights often cause “innocent” men to wake up in strange beds, in which they really had no right being in! “Must have been those dang lights again!” It’s incredible what a man will come up with when his wife has him against a wall.

‘Will-o'-the-Wisp Dance’ (1901) by Hermann Hendrich.

‘Will-o'-the-Wisp Dance’ (1901) by Hermann Hendrich. (Public Domain)

Reasoning with the Light Phenomena

Not some, but all the ancient stories and myths attempting to explain the origins of this light phenomena use supernatural mechanics, generally pertaining to the voyage of the soul after death. In 16th century England, it was proposed that the idea of a soul being “seen” by a human was preposterous and ‘bioluminescence’ became a popular theory, that the greenish glow was caused by fireflies or honey fungus.

However, the most accepted historical theory was presented by Allesandro Volta just after he discovered methane in the summer of 1776. He also invented the first battery; thus, the volt is named after him. Volta believed that lightning was interacting with swamp gases and caused the ghostly flickering lights, but his theory was extremely controversial at the time because it did not explain why “Will-o’-the-Wisps appeared to retreat when approached (this in an appropriate moment to face palm). Over a century passed before Volta’s theory was proven to be, more or less correct, when in the early 20th century it was discovered that Will-o’-the-Wisps were caused by burning gases defined as “swamp gases” or “marsh gases.”

Count Alessandro Volta (1745 - 1827). Born in Como, Italy.

Count Alessandro Volta (1745 - 1827). Born in Como, Italy. (Public Domain)

Decomposing organic matter in persistently wet areas goes through a process known as “aerobic decomposition” - which is different to what goes on in your compost heap/pile/bin. Because plants and animals are composed primarily of carbon, hydrogen, and oxygen, when they decay in the presence of oxygen they turn into water, carbon dioxide, and energy (heat). In swampy places, however, aerobic decomposition is restricted and in the absence of air, the matter is broken down by anaerobic bacteria. This is where the magic happens. The by-products of this deoxygenated decomposition process are methane, carbon dioxide, nitrogen, and phosphines - the latter of which are highly-toxic flammable gases. Phosphines are also so unstable that when exposed to air they can burst into spontaneous flames unpredictably.

‘The Effect of Marsh Gas on Your Perception.’

‘The Effect of Marsh Gas on Your Perception.’ (Russ Seidel/CC BY NC SA 2.0)


When you look into the science of this particular light phenomena the lighting dynamics of ancient myths and legends become even clearer. For example, burning phosphines in swamps not only form an intensely bright greenish light, but they also make thick white clouds. The dense white mist amplifies the apparent size of the greenish flame and this visual illusion accounts for the reports of the wisps looking like the ghostly apparitions of spirits/souls of dead people.

Will o the wisp.

Will o the wisp. (Public Domain)

And finally, we can shine light onto another mythological archetype by considering that nearly all stories of the lights tell of the “souls” or lights “moving away” and “dispersing” when approached. When an object moves towards this airborne chemical reaction, the air displacement causes a circulation of warm and cool currents - which are no place for Will-o’-the-Wisps!

Top Image: ‘Will-o-the-wisp and snake’ by Hermann Hendrich.  Source: Public Domain

By Ashley Cowie



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"Will-o'-the-wisp". The American Heritage Dictionary of the English Language. Houghton Mifflin. 2007.

Merriam Rouse, W. “The Fifollet.” Munsey’s Magazine.

Widder, Edith A. (1999). Archer, S.; Djamgoz, M.B.; Loew, E.; Partridge, J.C.; Vallerga, S., eds.  BioluminescenceAdaptive Mechanisms in the Ecology of Vision. Springer. pp. 555–58

APS Physics. (2006). [March 20, 1800: Volta describes the Electric Battery. APS News.

Cromell, Cathy. “Aerobic Versus Anaerobic Composting.” Dummies.

ashley cowie's picture


Ashley is a Scottish historian, author, and documentary filmmaker presenting original perspectives on historical problems in accessible and exciting ways.

He was raised in Wick, a small fishing village in the county of Caithness on the north east coast of... Read More

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