Who is Spriggans, Dr. Fallow from The Girl Who Circumnavigated Fairyland in a Ship of Her Own Making and what is their importance?

Spriggans are a three-fingered, sharp-clawed kind of fairy who dwell in the city of Mercurio, the capital of Autumn. Spriggans celebrate the movement and transformations of nature, and are constantly engaged in studying its many aspects. Dr. Fallow is a Spriggan leader and elder who, with the help of a couple of his more accomplished students, explains the nature of Autumn to September and warns her about the Worsted Woods. Perhaps most importantly, at least for September, he also dispels her illusions about what she's been eating, telling her that in spite of her precautions and against the warning of The Green Wind, she has been eating fairy food all along.