The Glaistig is a water faerie who is part alluring woman and part goat. She hides her cloven hooves under long flowing gowns and uses her good looks to entice men to dance with her, and when they are completely under her spell, she feeds on their blood. But on a gentler note she is kind to children and old people. On the island of Iona local women used to leave offerings of milk on the Glaistig Stone every evening as she lived nearby in a cave. In return for this kindness the Glaistig would guard their livestock during the night.
At Lochaber in Scotland a smith once caught a Glaistig and refused to release her until she gave him a herd of cattle; the cattle duly appeared. But the smith was still not satisfied; he demanded a house that neither enemy or faerie could harm.
The Glaistig summoned all the goblins from the surrounding countryside and they set to work building the house. It was completed in one night; the last piece was put in place just as the cock crowed. The goblins disappeared but not the Glaistig as she was still a captive of the smith.
She offered her hand to complete the bargain but the smith , obviously not trusting the faerie, burnt it with a red hot poker. The poor creature ran screaming into the hills where she bled to death.
The surrounding ground and plants have ever since been stained red with her blood.
Faeries and Folklore of the British Isles