Source: Greek mythology, Jason and the Argonauts, D&D
Threat Assessment: 4. A fusion between women and birds, they are foul and fowl creatures. A harpy is sent against those who have annoyed the Gods, so in actual fact if you have a harpy problem that's the LEAST of your worries.
Limitations: Not too bright, wings can be entangled in nets.
Personal note: They are known mostlly for taking food from a blind man which even if ordered by the Gods is pretty much a dick move.