The will-o'-the-wisp, also known as will-o'-wisp, is sometimes called jack-o'-lantern, "spooklights," or "ghost lights." It is a phenomena of anomalous natural lights, often, when they are seen at all (which is rarely) found floating over a bog. References to will-o'-the-wisp date back to at least the Middle Ages.
One early poem about the subject goes as follows:
There was in every hollow
A hundred wrymouthed wisps.
—Dafydd ap Gwilym (trans. Wirt Sikes), 1340
A common Latin name for the phenomena, ignis fatuus, which means "foolish fire," also suggests that people have been seeing it for at least a thousand years. Will-o'-the-wisps are small floating lights, sometimes seen in groups, that display a variety of movement patterns. These including stationary, slow movement, or the most famous: erratic, darting movements that some say are reminiscent of intelligence. The darting movement inspired many folktales, told throughout Europe and Russia, that a will-o'-the-wisp is actually a small lump of burning coal held by the lost spirit of a man denied entrance to both Heaven and Hell. The doomed spirit uses the light to lead travelers astray.
The traditional jack-o'-lantern carved out of a pumpkin at Halloween was actually named after the myth of will-o'-the-wisp. One version of the story says that the spirit put the burning lump of coal into a carved pumpkin. Other cultures view the will-o'-the-wisp as an indication of the location of buried treasure. Anyone seeking such a treasure would have had quite a difficult time digging in the bog. The phenomena appears to be worldwide, with traditional names for will-o'-the-wisp in places as diverse as the Philippines, Thailand, Norway, Utah, Lithuania, and Japan.
Scientists have provided at least a couple possible explanations for the phenomenon of will-o'-the-wisp, but none of these have been extensively verified. The most common explanation put forth is that will-o'-the-wisp is generated by the oxidation of methane gases and hydrogen phosphide produced by the decay of organic material in bogs. These chemicals has been shown to provide light when combined under laboratory conditions. Experiments by Italian chemists Luigi Garlaschelli and Paolo Boschetti have been cited, though independent confirmation has thus far been lacking.
Another possible explanation is that will-o'-the-wisps are synonymous with "earthlights," lights thought to be generated by piezoelectric (pressure-to-electricity converting) materials, such as quartz, being put under tectonic strain. This would partially explain the occasionally erratic movement of will-o'-the-wisps. Still, extensive experimentation of confirmation of this hypothesis has not yet been conducted in earnest.