Will-o’-the-Wisp

For centuries, people crossing wetlands at night told of a small, pale flame – bluish or yellow – that hovered above the reeds, drifted ahead of them and retreated when approached. Follow it, the stories warned, and you would be led off the safe path into the mire. In England it was Will-o’-the-wisp or Jack-o’-lantern, a man condemned to wander with a torch (a “wisp” of burning straw); in Wales and parts of England a corpse candle, foretelling a death; in Germany the Irrlicht, “wandering light”; in France the feu follet. The Latin ignis fatuus, “foolish fire”, appears in 16th-century Germany as a learned rendering of the German name.

Almost every wetland culture has its own version. In Bengal fishermen speak of the aleya, marsh lights linked to the ghosts of drowned fishermen. In Japan hitodama, floating souls, and kitsunebi, fox-fire, are associated with graveyards and with foxes. In Argentina and Uruguay the luz mala, “evil light”, is feared on the open plains, and in Brazil the boitatá is a fiery serpent. In Europe the lights were explained as souls in purgatory, unbaptised children, fairies, or the spirits of people who had moved boundary stones in life.

The wisp is also one of the first ghost phenomena that natural philosophers tried to explain. In the 16th century the Swiss theologian Ludwig Lavater, in his book on ghosts, already argued that many such lights had natural causes. In 1776 the Italian physicist Alessandro Volta, who had just identified methane bubbling from marsh mud, suggested that electrical sparks might ignite this “inflammable air” to produce the lights. The leading modern hypothesis adds phosphine and diphosphane – gases produced by decay that can ignite spontaneously in air and could set methane alight. Lab attempts have had mixed results: in 1980 the Leicester University geologist Alan Mills produced a cool glowing cloud from crude phosphine and natural gas, but its light was green and it gave off acrid smoke; in 2008 the chemists Luigi Garlaschelli and Paolo Boschetti at the University of Pavia achieved a faint, cool light using phosphine chemistry, though not a perfect match for the classic descriptions.

In September 2025 a Stanford team led by Yu Xia, working with the chemist Richard Zare, published a new idea in PNAS: tiny electrical discharges, or “microlightning”, between charged methane bubbles in water, filmed at 24,000 frames a second. Outside chemists called the work intriguing but noted that it used purified water and produced sparks rather than a swamp-sized glow, so whether it explains real will-o’-the-wisps remains open. Other suggestions over the years have included bioluminescent fungi and insects, and even barn owls with glowing plumage.

Sightings are now rare, and the most common explanation is simply that the habitat has gone: the great wetlands where wisps were reported, such as the English Fens, were drained for farming from the 17th century onwards. The lights live on in language – the jack-o’-lantern carved at Halloween takes its name from them – and in later ghost-light legends such as the Brown Mountain Lights of North Carolina and the Marfa Lights of Texas.

A small, pale flame or glowing ball – bluish, white, yellow or greenish – floating a little above the ground over marshes, bogs, peat and graveyards; lights that bob, drift, go out and reappear further away, seeming to retreat when followed; occasional reports that the flame gave off no heat.

Wetlands, fens, peat bogs and churchyards, usually on still, warm nights in late summer and autumn, and most often reported by travellers on causeways and paths across marshland.

The wisp appears in Milton’s Paradise Lost as the “wandering fire” that misleads the night traveller, and became a byword for anything that leads people astray. It gave its name to the Halloween jack-o’-lantern, features in Goethe’s Faust, in Tolkien’s Dead Marshes and in the Harry Potter books’ hinkypunks, and inspired painters such as Arnold Böcklin. Ghost lights from North Carolina’s Brown Mountain to Australia’s Min Min light are its modern relatives.