Poem of the Week 3/6/2012: from Romeo and Juliet

MERCUTIO:
O, then I see Queen Mab hath been with you.
She is the fairies' midwife, and she comes
In shape no bigger than an agate stone
On the forefinger of an alderman,
Drawn with a team of little atomies
Over men's noses as they lie asleep;
Her wagon spokes made of long spinners' legs,
The cover, of the wings of grasshoppers;
Her traces, of the smallest spider web;
Her collars, of the moonshine's wat'ry beams;
Her whip, of cricket's bone; the lash, of film;
Her wagoner, a small grey-coated gnat,
Not half so big as a round little worm
Pricked from the lazy finger of a maid;
Her chariot is an empty hazelnut,
Made by the joiner squirrel or old grub,
Time out o' mind the fairies' coachmakers.
And in this state she gallops night by night
Through lovers' brains, and then they dream of love;
O'er courtiers' knees, that dream on curtsies straight;
O'er lawyers' fingers, who straight dream on fees;
O'er ladies' lips, who straight on kisses dream,
Which oft the angry Mab with blisters plagues,
Because their breaths with sweetmeats tainted are.
Sometimes she gallops o'er a courtier's nose,
And then dreams he of smelling out a suit;
And sometimes comes she with a tithe-pig's tail
Tickling a parson's nose as 'a lies asleep,
Then dreams he of another benefice.
Sometimes she driveth o'er a soldier's neck,
And then dreams he of cutting foreign throats,
Of breaches, ambuscadoes, Spanish blades,
Of healths five fathom deep; and then anon
Drums in his ear, at which he starts and wakes,
And being thus frighted, swears a prayer or two
And sleeps again. This is that very Mab
That plats the manes of horses in the night
And bakes the elflocks in foul sluttish hairs,
Which once untangled much misfortune bodes.
This is the hag, when maids lie on their backs,
That presses them and learns them first to bear,
Making them women of good carriage.
This is she!


William Shakespeare  from Romeo and Juliet


A few fundamental puzzles for this passage -


Who is Queen Mab and what does she represent? (She is a midwife for faeries, or at least so says Mercutio. She does not actually seem to give birth to anything in the poem... so is this her primary role?)


Is she just some mischievous character or fantastic being? Does she have a psychological function? What does she reveal about the people that she encounters? Is she good for them or bad for them?


And why this prolonged discussion of her chariot in the beginning - does it have a function, or is it mere decoration? Does it matter that she's small?