Fairy Facts: Cait Sìth

 A recent discussion on social media has motivated me to start a small series which I am going to call 'fairy facts' which will offer a brief overview of specific types of beings often labelled as fairies or within the wider purview of the subject. This will not be an in-depth full article - I have already written a book, A New Dictionary of Fairies, that deep dives into various fairies and folklore Katherine Briggs style and I am not going to do that again here. But I am going to offer a solid basic intro to each one that can hopefully help people understand this folklore better and dispel some popular misunderstandings. 

So, to start lets look at a victim of meme'ing misinformation, the Cait Sidhe or more properly the cait sìth.

not a cat sidhe, just a regular cat

Name: Cat sìth in Gaidhlig, Cat sidhe in Irish, both meaning 'fairy cat' or 'cat of the Otherworldly mounds'
    plural is cait sìth or cait sidhe

Description: a medium-to-large-dog-sized black cat with a spot of white on its chest

Found in primarily Scottish and to a lesser extent Irish folklore

Folklore: despite the name a cat sìth isn't a cat per se, but rather is either a fairy in the shape of a cat or a witch who has transformed into a cat. As a witch it is believed they can change into their cat form 8 times and change back to human form but if they change a 9th time they will be trapped as a cat forever. In stories of the fairy in cat form they sometimes speak or act in anthropomorphic ways, and its believed they walk on two legs when they think they won't be observed. 
  Cait sìth are believed to steal the souls of the newly dead, so there are a variety of wake practices which were  focused on preventing that, including attempts to distract or delay the fairy cat from reaching the corpse. 

See: Campbell's The Gaelic Otherworld for more on cats and witches/witches in the form of cats

Where It Gets Muddy: much of the folklore that is commonly found about Cait sìth comes from a single website from 2000, which didn't cite any sources for its claims. This is where the idea that a bowl of milk would be left out on samhaine [sic] for the cat sidhe comes from, for example. While purporting to share scottish folklore the website uses Irish spellings and uses the plural cait sidhe in place of the singular, suggesting caution should be applied to the material. Nonetheless nearly a quarter century on from its start the material has become widespread and has been accepted into the modern folklore corpus. 

What They Aren't: cait sìth are not a breed of cat, although it is thought that they may have been inspired by the Scottish Kellas cat. They aren't any type of human-world cat nor are they housepets in any way. Despite the name and proliferations of twee memes, the cat sidhe isn't simply the fairy world equivalent of a human world cat, but is best understood as a humanoid spirit in the shape of a cat.