The Will o’ the Wisp a natural phenomenon seen by nighttime pedestrians near bogs, swamps, or marshes. They have been described in folk tales as atmospheric ghost lights, with their specifics being tailored to the culture the legends are presented in. The lights are generally portrayed as being wielded by a malevolent entity or prankster intent on misleading travelers with a wayward lantern or torch.

The term “wisp” refers to a bundle of sticks or a paper used as a torch. Will is the male moniker given to the protagonist, who is often said to be sentenced to roam a swamp or marsh to atone for transgressions.

The Will o’ the Wisp has been seen less frequently since the advent of artificial lighting and because many wetlands have been drained and converted to farm acreage.

Indeed, there is a clear scientific reason for Will-o’-the-Wisp sightings. They occur when phosphine, diphosphane, and methane all oxidize as they produce photon emissions. Once phosphine and diphosphane mixtures ignite oxygen and methane, the results produce ghostly images. Furthermore, phosphine produces phosphorus pentoxide, which in turn forms phosphoric acid upon contact with water vapor. This causes the viscous moisture described by witnesses.

Additionally, the apparent retreat of the Will o’ the Wisp when approached can be explained by the disturbing of the air by nearby moving objects, which causes gasses to disperse. This was observed in 1832 by Major Louis Blesson, who noticed that water was covered by iridescent film and, that during the day, bubbles were observed rising from the wetlands. That night, Blesson observed bluish-purple flames in the same areas and concluded that it was connected to rising gas.

There is also a school of thought that some Will o’ the Wisp occurrences may be geologic in origin, as they might be piezoelectrically-generated under tectonic strain. The hypothesis holds that strains which move cracks in Earth’s crust could also heat up rocks, vaporizing the water contained within. Rock or soil containing quartz, silicon, or arsenic, could likewise produce electricity, which would then rise to the surface, resulting in the haunting image. If true, this could explain why the lights often seem electric or erratic.

Further, the phenomenon may result from the bioluminescence of forest dwelling microbes, insects, and larger animals. The eerie glow emitted from some fungal species during chemical reactions form white rot and this could also be interpreted as atmospheric ghost lights.