The glaistig is a faerie that is one part sexy woman, one part goat. She wears a flowing green dress to hide her beastly features. It is said that she lures men to dance with her before feeding upon them by drinking their blood. But like many faeries, she also has a benign side to her personality, and has a gentle hand when tending children or the elderly. She has even been known to herd cattle for farmers.
I love this kind of duplicity in faeries. It makes it seem like whatever terrible quality they might have is merely a consequence of their nature rather than any malevolent intent. That’s just how they are, and there’s no reason why a lovely woman in a green dress can’t care for Nana or take Bessie out grazing. Just don’t dance with her.
Source: Froud, Brian; Lee, Alan, Faeries, Harry N. Abrams, Inc., 1978.