WILL-O’-THE-WISPS’ MYSTERIOUS ORIGINS EXPLAINED BY CHEMISTRY

Leading lightPhotograph: Bridgeman Images

October 24, 2025

Annie Roth

A newly discovered molecular phenomenon is responsible for the spectral balls of light seen in swamps and cemeteries

For hundreds of years, people taking a stroll through a swamp or cemetery at night have witnessed floating balls of flickering blue light appearing suddenly. The inexplicable phenomenon has inspired many a ghost story. Welsh poet Dafydd ap Gwilym, recording it for the first time in AD 1340, wrote, “There was in every hollow a hundred wrymouthed wisps.”

Though Gwilym called these ethereal lights “corpse candles,” they later took on many names, including jack-o’-lantern, friar’s lantern, and will-o’-the-wisps. Though many different cultures developed their own folklore around will-o’-the-wisps, the strange lights were generally believed to be spirits with ill intent.

Scientists have long searched for a scientific explanation for the eerie occurrence but have come up short. They’ve theorized that burning gases produced by organic decomposition produce these otherworldly balls of light but had no idea what was igniting the gases. Now, after hundreds of years of speculation, scientists at Stanford say they have an answer.

In a new study, a team of researchers presented evidence that a spontaneous electrical discharge can occur between methane microbubbles rising and bursting in water. The study, published in September in the journal Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2521255122), explains how this random electrical discharge, which the scientists dubbed “microlightning,” not only provides an ignition source for will-o’-the-wisps, but is an entirely new form of chemical synthesis.

A spark of genius solves will-o’-the-wisp mystery

Isaac Newton was one of the first to ponder will-o’-the-wisps’ mysteries: He mentioned them in his 1704 book, Opticks, describing their weak flames as different from those of a candle or burning wood.

At that time, scientists had already suggested that burning swamp gases might be to blame for will-o’-the-wisps. Surprisingly, the advancement of modern technology didn’t help solve the enigma.

That’s because, as industrialization spread worldwide, the swamps, bogs, wetlands, and water-logged cemeteries associated with will-o’-the-wisp sightings were drained and developed. Over 60 percent of Earth’s wetlands have been lost since 1900, and, to this day, no one has ever filmed or photographed the ghostly events.

Solving the mystery of will-o’-the-wisps was not something study leader Richard Zare, a chemist and professor of natural science at Stanford University, set out to do. Several years ago, Zare wanted to know why tiny water droplets were so different from bulk water when it came to chemical reactivity.

He’d noticed that when water breaks into microdroplets, a portion of its H2O molecules undergo a “Jekyll-and-Hyde transformation” into hydrogen peroxide. In his quest to determine why, Zare discovered that a strong electric field generated at the interface of water and air drove this transformation. At this interface, electricity activates water molecules, forming unstable molecular fragments that react with other molecules to yield hydrogen peroxide.

Eager to better understand the electric field generated at the interface of water and air, Zare and his colleagues built a machine that pumps micrometer-sized bubbles of air and methane into a container of water. Using a high-speed imaging camera, Zare and his colleagues saw exactly what was happening when the bubbles burst at the surface, and what they saw shocked them.

Microlightning in action

Under dense bubbling conditions, the camera caught localized flashes of light indicative of nonthermal methane oxidation. Using spectroscopy, thermal probes, and mass spectrometry, the researchers determined that as the methane microbubbles moved, coalesced, and split on their way to the surface, some underwent charge separation.

When some of the bubbles with opposite charges came together, they produced a microlightning discharge. What’s more, these flashes of microlightning also initiated nonthermal oxidation of the methane, producing the same cool, blue flames seen in will-o’-the-wisps.

A new form of chemical synthesis

This discovery “solves a mystery that has been a puzzle for centuries,” Gaurav Chopra, a professor of chemistry at Purdue University, says. To Chopra, who wasn’t part of the research, it also “reframes how we understand interfacial chemistry.”

Xin Yan, associate professor of chemistry at Texas A&M University, agrees. The existence of microlightning expands “our understanding of spontaneous electrochemical activity in natural systems,” she says.

Such a discovery has broad implications not just for chemistry but for other fields of science, such as climate modeling. For instance, the research “suggests new mechanisms for methane oxidation in aquatic environments, potentially influencing models of greenhouse gas cycling,” Yan adds.

Improving the accuracy of climate models is just one of many important implications of the study, study leader Zare says. For instance, microlightning might have even played a role in how molecules formed the early building blocks of life.

“This is bigger than just will-o’-the-wisp,” he says.

This article was originally published in Chemical and Engineering News on Friday, October 24.