During WWI, when an Allied soldier wanted to read a map or letter at night, his choices were very limited- wait until it gets light, or risk exposing himself to enemy fire by firing up something like a bright lamp or lighter, if he had one. However, there was a seldom discussed third choice that was readily available- gather up a few glow-worms.
The usual method was to pluck up enough glow-worms to suit your particular lighting needs and put them into a jar or bottle. Though the strength of the glow tended to vary, even just a few of them was usually enough for a given soldier to read a letter or map without being too bright to risk attracting enemy fire. If you wanted brighter, you could pluck up several dozen choice specimens and have yourself a natural lantern.