Study suggests cause of mysterious will-o'-the-wisps
Scientists may have uncovered the origins of will-o'-the-wisps, the eerie lights long reported in swamps and marshes. A new study proposes they result from the spontaneous combustion of phosphine gas produced by decaying organic matter. This explanation could resolve a centuries-old natural mystery.
Will-o'-the-wisps, also known as ignis fatuus or fool's fire, have captivated and frightened people for centuries. These flickering lights, often seen hovering over wetlands at night, feature prominently in folklore across cultures, from European ghost stories to Indigenous tales in the Americas.
A study published on October 10, 2024, in the journal Atmospheric Chemistry and Physics offers a scientific breakthrough. Researchers led by atmospheric chemist Matthew Johnson at the University of Copenhagen simulated the phenomenon in a lab. They found that phosphine (PH3), a highly flammable gas generated by bacteria breaking down organic material in oxygen-poor swamp environments, can ignite spontaneously upon contact with air.
"The key is the low ignition energy required for phosphine," Johnson explained. "Even a small spark or static discharge in humid conditions can set it off, creating the observed blue-green glow and erratic movement as the gas rises."
Previous theories have included bioluminescent fungi, piezoelectric sparks from quartz in the soil, or even distant car headlights. However, the Copenhagen team's experiments ruled out many of these by recreating the lights using controlled releases of phosphine and methane mixtures. The lights lasted seconds to minutes, matching eyewitness accounts, and emitted a spectral signature consistent with phosphate combustion.
This discovery builds on earlier work from the 18th century, when Italian physicist Alessandro Volta first isolated marsh gases. Yet, direct observation of will-o'-the-wisps remains rare due to their unpredictability and remote locations. The study emphasizes that climate change, by altering wetland decomposition rates, might influence future sightings.
While not all historical reports may fit this model—some could stem from other gases like diphosphane—the research provides a plausible mechanism for most cases. It underscores the intersection of chemistry and folklore, demystifying a phenomenon once attributed to spirits.