The harpy, like pretty much all the other Naked Lady Monsters of any mythology, is a patriarchal reversal of earlier matrifocal religious practice. Birds are strongly linked with goddess figures around the world (along with snakes and fish), and that association was frequently altered to produce “monsters”. In modern Western art, we frequently represent harpies’ monstrous characteristics by exaggerating their features to ensure that they in no way align with conventional models of gendered attractiveness – in other words, they’re more monstrous because they’re not hot.
In the coming year, whenever you prepare to spring a monster on your players, think about the origins of that monster, especially the hominid ones. Like the harpy, is it at its core a representation of the desire to justify violence against women? Like the succubus, is it a literal demonization of an externally-imposed idea of female sexuality? Or is it simply another repaletted orc, a male power fantasy: something you can kill without consequences and come home a hero (and let’s not even get into the explicitly violent origins of half-orcs in D&D)? And if you’re the player, ask yourself why the GM is using monsters in this particular way. What does it say about the GM, about his or her expectations of the players, about society as a whole?