Will-o-the-Wisps are said to be the souls of the damned that have come to damn the souls of the living. They appear as lights glowing in a marsh.
It is best to avoid the Will-o'-the Wisps, and to do so one should aviod whistling at or near them. If they start to attack you, throwing a needle at them is said to drive them away.
Will-o'-the-Wisps are also known as Jack O' Lanterns.