Marsh Will-o’-the-Wisps Sparked by Strange Chemistry
NEWS | 02 December 2025
An illustration of an ignis fatuus, or will-o’-the-wisp, by Josiah Wood Whymper from the book Phenomena of Nature (1849). I agree my information will be processed in accordance with the Scientific American and Springer Nature Limited Privacy Policy . We leverage third party services to both verify and deliver email. By providing your email address, you also consent to having the email address shared with third parties for those purposes. Some call them will-o’-the-wisps; others call them ignis fatuus, Latin for “foolish fire.” Whatever the name, for centuries people have reported seeing these eerie, faint blue flames hovering over marshes, bogs, and other wetlands. Various cultures have interpreted the ephemeral aberrations as fairies, ghosts or spirits. Scientists have offered a different explanation: the lights form when methane and other gases from decaying material react with oxygen and briefly ignite, producing a flamelike glow. But one big mystery remained. Although will-o’-the-wisps are not actual flames and occur at ambient temperatures, they still have to ignite somehow. The source of that ignition has been unknown to research. Now a paper published in the Proceedings of the National Academy of Sciences USA seems to provide an answer: microlightning, or tiny, spontaneous sparks of electricity that occur because of differences in charge on water droplets’ surfaces. These droplets form when water bubbles containing methane rise and burst at the surface of the marsh, and the resulting sparks ignite the methane to create will-o’-the-wisps’ telltale luminescence. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. “Your first reaction when you hear about this finding might be, ‘Okay, will-o’-the-wisps are these ghostly, spooky things, but so what?’” says Richard Zare, a physical chemist at Stanford University and senior author of the findings. “In fact, the phenomenon we found—related to how chemistry can be driven at interfaces—is profound.” Water is neutral, which means it does not typically carry electric charge. But as early as 1892, scientists noted that fine droplets of water can be positively or negatively charged in an aerosol such as waterfall spray or fog. Zare’s group found that when two oppositely charged droplets get close to each other, electricity can suddenly rush between them, creating microlightning. Zare and his colleagues first described and coined the term “microlightning” in a study published in March in Science Advances. In that study, they showed that when water sprays, some of the resulting microdroplets pick up opposite electric charges that can spark flashes of energy when the drops get close to one another. This spark can drive chemical reactions in the surrounding air that result in simple organic molecules. Zare and his colleagues hypothesized that this process might have generated some of the chemical building blocks for life on Earth. Although the new study has less lofty implications, Zare says the mechanism is basically the same. His team’s experimental setup was simple: In a beaker of water, the researchers introduced bubbles composed of methane and air. They captured high-speed videos of the bubbles hitting the surface of the water, forming microdroplets and producing tiny, faint flashes of light. The researchers also used mass spectrometry to provide additional evidence that the microlightning they observed generated the energy to drive a reaction between methane and oxygen, converting the gases into different compounds. The “well-executed” research “strongly suggests” that microlightning is indeed the natural ignition mechanism responsible for will-o’-the-wisps, says Wei Min, a chemist at Columbia University, who was not involved in the work. But some mysteries endure, Min adds. One big unanswered question, for example, is how, exactly, the strong electric fields form on the droplets’ surface in the first place. The answer, he says, will have “broad implications for physics, chemistry, biology and engineering.”
Author: Sarah Lewin Frasier. Rachel Nuwer.
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