The Element Encyclopedia of Witchcraft: The Complete A-Z for the Entire Magical World - Judika Illes 2005
Tylwyth Teg are Welsh spirits usually described as resembling humans although manifesting in assorted sizes: some are human-sized, some are approximately the height of a man’s knee while others are tiny, although, as they are also renowned shape-shifters, perhaps this is a moot point. Their name means the “Fair Family” but this may be a euphemism for these Welsh fairies.
Tylwyth Teg live in organized societies ruled over by a king, Gwyn ap Knudd. There are both male and female Tylwyth Teg. They typically dress in green although the king’s court allegedly wears blue and red silk.
Tylwyth Teg prefer to live in remote places: wooded areas in the mountains, or lonely islands within lakes or off the Welsh coast. They are nocturnal, emerging at night to make music and dance in the moonlight in fairy rings. They adore music and have been accused of kidnapping particularly skilled human musicians and forcing them to stay and play for them.
A human caught within a fairy ring is obliged to dance with the Tylwyth Teg for a year and a day, although carrying a rowan twig grants you free passage through their territory. Plough through one of their fairy rings, even by accident, and be cursed for life. Their mainstay meal is milk with saffron. They dislike salt and iron and are among the fairies accused of stealing children and leaving changelings behind.