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Ignis Fatuus

Latin 'Foolish Fire,' Scientific Name for Will-o'-the-Wisp

Ignis fatuus is Latin for 'foolish fire,' the scientific name for the natural phosphorescence observed in marshlands. Equivalent to English 'will-o'-the-wisp' and Korean 'dokkaebi-bul,' it's a universal European folk phenomenon — likely natural methane combustion — interpreted as bluish lights that lure travelers astray. Treated simultaneously as natural phenomenon and supernatural spirit since medieval times, it appears throughout English literary classics by Shakespeare and Milton.

Origin

Ignis fatuus is Latin for 'foolish fire' and is the scholarly name for the natural phosphorescence observed over marshland. It is the Latin equivalent of the English 'will-o'-the-wisp,' German 'Irrlicht,' and French 'feu follet,' and was the standard term in 16–18th-century natural histories.

Features

Bluish phosphorescence over marshes
Modern interpretation: spontaneous ignition of methane gas
In myth, the scholarly name for the soul of a lost wanderer
Visible only in deep darkness
Recedes when approached

Stories

Both the scholarly name for the natural phenomenon and the Latin umbrella term for marsh-light folklore. Used in natural histories and as a learned name for will-o'-the-wisp in fantasy literature.

Weakness

As a natural phenomenon, dispersed by sunlight or strong wind. In myth, defeated by firm will and faith.