Night-haunts are winged creatures that eat the bodies of dead Faeries for the memories they contain. When someone fae dies, the night-haunts rapidly appear to take the body away. They leave an exact (humanized) replica behind. The Faeries made this arrangement with the night-haunts long ago. Without them, the bodies would remain forever, because faeries do not age or decay.
In certain circumstances, night-haunts can become Fetches, warning of an impending death. It is revealed by the Luidaeg that the night-haunts were a scourge among the Fae, eating both living and dead, until Oberon bound them to eat only the dead. If a night-haunt eats the blood of the living, they will become a Fetch, tied to the person who's blood they consumed until their death. Fetches live as long as their tied Fae does, and they eventually fade afterwards. There is no known method to prevent this, but Amandine's intervention had allowed May to exist as her own person without being tied to Toby. 
Night-haunts take the face of the body they've eaten most recently.
There are multiple flocks of night-haunts, scattered all over the world. They usually live in groups of about thirty to sixty, depending. They have a higher than usual birth rate for fae, because they also have a higher than usual death rate; a night-haunt who doesn’t manage to taste a death before their last one runs out will literally starve and disappear.
See Also Edit
- ↑ Rosemary and Rue, ch. 26
- ↑ 2.0 2.1 Rosemary and Rue, Ch. 4
- ↑ http://seananmcguire.tumblr.com/post/98622774765/a-nighthaunt-question-from-rereading-the-books