In Shakespeare's play, Romeo and Juliet, Mercutio and Romeo discuss Queen Mab, in Act One, scene four. The discussion begins because Romeo has had a bad dream, and he thinks the dream is an omen—that it is telling him it is unwise for them to crash the Capulet party.
According to Mercutio, Queen Mab is...
the 'fairies’ midwife,' or the fairy responsible for bringing dreams that fulfill the wishes of the dreamer (l.54)
Queen Mab is a tiny little "fairy" who drives "over men's noses as they lie asleep." Mercutio provides minute details that describe several things. He speaks about the tiny coach she travels in, made of a hazelnut shell, with wheels that have spider's legs for spokes. He also lists the people whose dreams she visits: "lovers' brains...courtiers' knees...lawyers' fingers...ladies' lips...a parson's nose...and a soldier's neck."
Mercutio also describes the mischief she practices while the world sleeps. Queen Mab braids the manes of horses and mats the hair of old women (hags).
Mercutio's speech is a long one, surprisingly whimsical from a character who so often seems impatient and cynical.