Harpies are part human, part bird. Originally they were created by Eonil and were both male and female harpies but at some point corruption of Ghor made the female harpies cast a curse on their male counterparts. As a result they could no longer produce living children with each other and instead were dependent on others for reproduction. Female harpies, now referred to as harpies would be able to mate with a man and lay eggs which produced female harpy children.
Because of Ghor’s corruption harpies are no longer able to disguise themselves as humans, but they still possess the power to seduce a man. They take pleasure in seducing the man of a new couple and thus destroying their relationship. They can also invoke jealousy for the same result.