"She isn't really a worm at all. Glow-worms are never worms. They are simply lady fireflies without wings."
"'She isn't really a worm at all. Glow-worms are never worms. They are simply lady fireflies without wings.'" - James and the Giant Peach
This is what the Centipede tells James Henry Trotter after he points out that the Glow-worm doesn't actually look like a worm at all, in Roald Dahl's early children's story James and the Giant Peach.
She might spend a lot of her time sleeping, but the Glow-worm provides the main source of light for James and his friends aboard the Giant Peach. As James says later, "...although this smacks a bit of eccentricity, it's really rather clever."
In the 1996 partially animated film version of James and the Giant Peach, Miriam Margolyes - who had also played Aunt Sponge - voiced the Glow-worm.