The Mythology & Folklore Database
If they show themselves, which normally happens only at nighttime, the people there have a ridiculing rhyme:
Heerwisch, Heerwisch, hah, hah, hah!
You're afire like straw, straw, straw!
You can hit me black and blaw!
More than one person came to misfortune because of this.
More than thirty years ago a young girl was walking by a swamp near Hänlein. She saw a will-o'-the wisp hopping along, and she rudely shouted out the rhyme. The will-o'-the wisp suddenly came fluttering toward her. The girl became frightened and ran as fast as she could toward her parents' house. The will-o'-the wisp was right behind her, beating at her with its fiery wings like a huge swamp-bird.
Deathly afraid, she reached the house and slipped inside, but the will-o'-the wisp came in with her, illuminating the entire entryway. He followed her into the main room. He struck with flames at everyone who got in his way, then flew up the chimney. Finally he danced across the rooftops like a fiery dragon.
The next day everyone, and the girl most of all, was black and blue from the will-o'-the wisp's blows.
It is believed that the will-o'-the wisps and fiery men are dead people who cannot find their eternal rest because of evil deeds that they committed while alive. Above all, they are dishonest land surveyors and those who moved boundary boundary stones, as well as farmers who plowed away land from their neighbors' fields. Everywhere in Germany such sinners are believed to be the fiery men.
In northern Germany will-o'-the wisps are believed to be the souls of unbaptized children.
In Thuringia [Thüringen] they say to someone who is running very fast, "You are running like a fiery man."