Will-o’-the-Wisp: Monstrous Flame or Scientific Phenomenon?

These elusive blue flames have been reported globally and inspired a wealth of folklore. But what exactly is a Will-o’-the-Wisp? Also commonly called “ignis fatuus” or “corpse-candle” the glowing atmospheric phenomenon has a reputation for causing mischief and even death. But are they really a supernatural phenomenon or something more worldly?

AIRED: October 05, 2021 | 0:09:58

- [Emily] Ethereal and fleeting,

mesmerizing and elusive,

these floating blue flames have been a mainstay

in European folklore

since at least the 14th century.

You may have heard of the name will-o'-the-wisp,

but do you know what it is?

Stories of sentient blue flames floating,

and bouncing across marshes and bogs,

permeate cultures from Northern Europe

to Australia.

While some stories have faded into ephemera,

just as the floating blue flames

that inspired them,

these elusive creatures remain

mainstays of myth,

and legend in pockets across the globe.

So what are they?

Fairies, fireballs, ghosts,

atmospheric phenomena?

Here's the haunting history

of the will-o'-the-wisp.

(upbeat instrumental music)

I'm Dr. Emily Zarka.

And this is "Monstrum."

The will-o'-the-wisp

are most frequently described

as small moving blue flames

that hover a few feet off the ground,

and do not flicker.

Cold or cool to the touch,

if you're brave or reckless enough to touch one,

they can be found in marshlands,

bogs and swamps.

All treacherous places to wander

even without the alluring glow

of the will-o'-the-wisp

leading you deeper into danger.

Follow the will-o'-the-wisp's seductive dance,

and you may find hidden treasure

or a watery grave.

Stories of these elusive,

and inscrutable flames vary.

Some say spotting the floating flame

is an indication that someone

is blessed with the power of foresight,

but more often folklore,

and literature paints them as impish tricksters,

restless spirits or malevolent beings.

In Sweden, will-o'-the-wisps

are ghosts with lanterns

fated to wander aimlessly

for removing their neighbor's boundary markers.

In English tradition,

the blue flames are lights carried by elves.

And in Australia, the light may approach someone,

but anyone who tries to catch it will disappear.

Other tales say the lights are crafted by fairies

or even a fire species on its own.

In Belgium and the Netherlands,

they are the lost spirits of unbaptized children.

While in other places,

the floating flames are said to be

the wandering souls of unhappy women,

unrighteous men,

priests who have broken their vow of chastity,

or even those souls who escaped purgatory.

In fact, the ethereal-like leads

its most enduring name

will-o'-the-wisp or will-with-a-wisp

from the Saxon word wile for fraud,

trick, or deceit

and the Swedish word wisp,

meaning a small lit bundle of tinder.

Variations include will-with-the-wisp,

willy wisp,

and willow o' the wykes.

Essentially, the name hints that the light comes

from some trickster spirit holding a flame aloft.

Further north in Norwegian folklore,

the will-o'-the-wisp is called Hoberdy's Lantern,

Hobany's Lantern

or even Hob and his lantern.

Hob may come from the Norwegian hoppe,

meaning mare,

or the old Norse word hoppa,

which translates to leap or hop,

which might not be as obvious a name

as a deceitful bundle of tinder

until you know that the will-o'-the-wisp movement

often resembles the cantering motion of a horse.

Yet another moniker for the floating lights,

Jackie lantern or jack-o'-lantern.

Yes, that's right.

The carved pumpkins that adorn

many a stoop or doorstep

on Halloween actually borrow their name

from this mysterious light.

Jack-o'-lantern is of English language origin,

and simply means Jack of the lantern.

So when did we start hearing

about these creatures?

Well, the first recorded siting

of will-o'-the-wisp is described in a 1340 text

penned by Welsh poet Dafydd Ap Gwilym.

He wrote that, "In every hollow

live a hundred wrymouthed wisps."

He names the phenomenon Canwyll Corff,

Welsh for corpse-candle,

thereby introducing what will become

another common name

for the supernatural blue flames,

and associating the lights with death,

and burial sites.

The first appearance of the lights

in the English language occurs in 1563

under the name Ignis Fatuus.

Here they are described as,

"Foolish fire that hurteth not."

In another variation

of the will-o'-the-wisp myth,

the ghost lights are attributed

to a mischievous sprite called a puck,

which uses the light to lure humans

to fall into ditches, bogs, and pools,

and then laughs with their predicament

before fleeing.

Sometimes referred to in this form

as walking fire,

it can also appear as a horse, bull, or eagle,

but it is always a trickster.

Shakespeare adopts the name Puck

for the character of a shape-shifting sprite

in "A Midsummer Night's Dream."

First performed around 1596.

This Puck turns into a phosphorescent glow,

and hovers over the marshes at night

to trick travelers.

In "Henry IV."

He uses the name ignis fatuus

to refer to a ball of wildfire.

The will-o'-the-wisp even appears

in John Milton's famous epic poem,

"Paradise Lost."

As a malevolent distraction,

"A wandering fire compact of unctuous vapor,

which the night condenses,

and the cold invirons round,

kindled through agitation to a flame,

which oft, they say, some evil spirit attends.

Hovering and blazing with delusive light.

Misleads the amazed night-wanderer from his way,

to bogs and mires,

and oft through pond or poole."

Like many other references in literature,

and folklore,

Milton's will-o'-the-wisp is associated

with danger,

bad news and even death.

But over time, the elusive blue flame also became

a literary metaphor

for anything that is just out of reach,

a delusion one may chase endlessly,

but unsuccessfully.

Will-o'-the-wisp sightings

are reported across the globe,

and the frequency of their marshland appearances

points to a very real origin.

The stories may be made up,

but the lights themselves are not.

There's scientific truth to these reports.

Theories explaining

the will-o'-the-wisp phenomenon

circulated in scientific communities

for 100s of years.

In fact,

in 1704 Isaac Newton wrote in "Opticks."

Of the ignis fatuus as,

"Vapors shining without heat."

The vague statement unsurprisingly

sparked vigorous debate

in the academic communities

of the 18th and 19th centuries.

English folklorist and historian, Jabez Allies

traveled over Europe collecting stories,

and evidence of antiquity.

And in 1839 he got lucky with his own

firsthand experience

catching a glimpse of the mysterious flame.

Allies claims that while traveling

near Worcester in England,

he saw the will-o'-the-wisp.

He described the light as very clear and strong,

unwavering and much bluer in color than a candle.

He wrote,

"Sometimes it was only like a flash in the pan

on the ground;

"at other times it rose up several feet

and fell to the earth and became extinguished;

and many times it proceeded horizontally

from fifty to one hundred yards

with an undulating motion,

like the flight of the green woodpecker,

and about as rapid;

and once or twice it proceeded

with considerable rapidity

in a straight line upon or close to the ground."

Allies reports that the two nights in a row

he saw the phenomenon,

there were only minimal clouds,

and bright starlight.

Both evenings were rather warm and had no fog.

He speculates that the will-o'-the-wisps appear

on nights after a rainfall in the winter season.

Was Allies onto something?

What else could explain these odd flames?


Too small, and they glow with a yellow

or green flickering light.


The females do produce a bright light,

but don't fly.

Male glowworms fly, but don't glow.

St. Elmo's fire, perhaps?

The plasma-creating weather phenomenon

does produce a blue glow,

though it requires a strong electrical field

in the atmosphere,

and an encounter with a conductor

like the mast of a ship or the wing of a plane,

which doesn't appear

in reported will-o'-the-wisp sightings.

What about ball lightning?

Spherical, glowing, and capable of lasting

for longer than a brief flash, yes,

but only during thunderstorms

with ranges in color,

and usually accompanied by a hissing sound,

and a distinct odor.

Will-o'-the-wisp aren't associated

with any smell,

and only seem to appear a day

or more after rainfall or storm.

Perhaps then, dare I say it, luminous owls?

An unusual occurrence

in which the feathers of the bird

are contaminated by a fungus

whose metabolic process produces a glow

when the owl is in the dark.

But will-o'-the-wisp move more slowly

than owls typically hunt,

and don't tend to cover much ground.

The most likely explanation,

spontaneous combustion of marsh or swamp gas,

a rationale proposed at least

as early as 1729 by W. Durham

who, after observing the phenomenon

over half a decade,

directly refuted the hypothesis

that the lights were caused

by glowworms flying together.

Given the frequently reported occurrence

of the will of the will-o'-the-wisp

on marshlands, swamps and bogs,

swamp gas seems pretty plausible.

Made up of about 60% methane

as well as other components like carbon dioxide,

swamp gas is the by-product

of decomposing vegetation in areas

like swamps marshes and even landfills.

And in some rare cases,

if there is enough heat,

and oxygen produced by the metabolic process,

the gas can spontaneously combust,

and produce fire.

And nothing just happens to burn

with a blue flame and a yellowish glow.

Will the mystery of the will-o'-the-wisp

ever truly be solved?

Even today many people swear the will-o'-the-wisp

is a supernatural or paranormal experience.

Interestingly, there have been no modern

encounters with the will-o'-the-wisp,

and therefore no new data to add

to any potential debunking theories.

Perhaps there are no more will-o'-the-wisp

because we have drained,

and demolished so many marshes and lowlands.

Maybe we'll never know

what caused the glowing blue flames

spotted so many years ago.

And I kind of liked that.

Glow on mysterious fiery orbs.

Glow on.


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