Banshees
Little is known about Discworld banshees. Although the banshee of Gaelic folklore are always female (the Gaelic word "banshee" means "fairy-woman"), the only two banshee to appear in the Discworld books have been male, as all of the female banshees have now become extinct (see The Pratchett Portfolio, and The Truth). They are described as the only humanoid race on the Disc that can fly unaided.
Banshees are tall, lean figures, who appear to be wearing long leather capes. These are actually their folded wings. They have flight muscles like steel armour, but their skeletons are fragile. Banshees have two hearts and many rows of teeth.
The Discworld banshees seem to have evolved in the jungle, where they used their power of flight to help them hunt small (and many not-so-small) animals. This carnivorous instinct tends to backfire in Ankh-Morpork, where any uncooked animal is basically food poisoning on legs.
There appear to be two kinds of banshee, civilised and feral. Civilised banshees can apparently sense when a person is about to die. They will traditionally scream from that person's rooftop as a sign of impending death. However, Mr. Ixolite, the banshee featured in Reaper Man, has a speech impediment and prefers to leave a note instead (usually saying "Oooeeeoooeeeooee"). Hearing the scream of a feral banshee is also a sign that you are about to die, but the connection in this case is much more direct. Interestingly, though, Mr. Gryle the feral banshee worked as a killer for large amounts of money (not a registered Assassin), and berated himself for being unable to fight the urge to snatch pigeons out of the air as they scattered.
Read more about this topic: Undead (Discworld)