For this installment of fairy facts I wanted to discuss a popular but often misunderstood being, the Bean sidhe. I will note at the start that there is an ongoing debate about whether or not the Bean sidhe is a fairy or a separate type of being, but I am including her here because of the long standing translation of bean sidhe as fairy woman and her wider association with the Otherworld. I recommend Patricia Lysaght's book 'Banshee: The Irish death messenger' if you really want to deep dive into who and what the mná sidhe (banshees) are.
Name: Bean Sidhe (Irish), Ban-sìth (Scottish). Anglicized as Banshee, the term literally means 'Otherworldly woman'. In Ireland the bean sidhe may also be known regionally as the Bean Chaointe or Badb.
Description: Descriptions of these beings vary across stories. By some accounts they appear as old women with grey hair, while others describe younger women, sometimes blonde, whose eyes are red from weeping. In a few accounts of a Bean sidhe who is known by name as one of the Tuatha Dé Danann, like Clíodhna, they may be described as enchantingly beautiful. They may wear white, grey, or green, sometimes with red shoes.
In folklore they can take the shape of owls or of hooded crows.
Found: Ireland, Scotland, and related communities. Also becoming more common across popular culture.
Folklore: Although fairly localized to Ireland and parts of Scotland there is a wide array of Bean Sidhe folklore. This can roughly be broken up into three types: Death omens, Supernatural dangers, Fairy women. Each type has specific folklore surrounding it, although they are both part of one cohesive concept.
Death Omens. The Bean sidhe as death omen is perhaps her most well known role. It is said that all of the older Irish families have a bean sidhe who follows their family line, usually connected through ancestry, and who appears to wail before a death in that family. There are a range of stories of people in families hearing the bean sidhe before a death as well as those who are unrelated hearing a bean sidhe only to later find out that a local person died. The wailing or cry of the bean sidhe is extremely eerie, not comparable to any normal sounds, and is said to be a kind of keen or caoine, a mourning cry or song.
Supernatural Dangers. The cry or wail of the bean sidhe doesn't cause death or harm to those who hear it, but the bean sidhe herself can be dangerous in other ways. There are various stories of a person who finds a comb on the ground, sometimes of the roadway, takes it home, only to have an irate bean sidhe show up after dark demanding the return of her property. She circles the house, clawing and yelling to be given back her comb - eventually the person relents and passes the comb through a window, but clasped in iron fire tongs. After pulling the tongs back in they are found to be horribly twisted, hinting at the harm that the bean sidhe would have done to the hand that passed them out. There are stories on Duchas.ie as well of people who were chased by the bean sidhe, escaped, only to fall ill and die within a short period of time.
Fairy Women. The stories around the bean sidhe also include tales that don't fit easily into either previous concept and are usually simply descriptions of a person seeing a bean sidhe who is neither crying nor threatening them. For example, Fairy Faith in Celtic Countries recounts a story of a man who saw a bean sidhe by Lough Gur sitting on a rock and combing her hair. These types of tales often figure into the other two categories - in the above the bean sidhe is described combing her hair and the comb is a key part of many stories of the bean sidhe as a danger.
The folklore around the bean sidhe is complex. Some are said to be women of the Tuatha Dé Danann, including Áine, Clíodhna, and Aoibheall, who watch over family lines they are bound to. Some are less renowned women of the Otherworld who do the same thing for a similar reason. There are also an array of stories of human women who became mná sidhe: women who died in childbirth, women who committed a horrific offense or who died by violence themselves, or women who were professional keeners in life but failed to do their jobs well. In some the first cases the woman was only bound to act as a bean sidhe until the time that her natural life span would have ended; in the latter it is a less fixed period where she must 'earn' her place in the afterlife.
Where It Gets Muddy: A lot of the wider understandings of the bean sidhe have been shaped by popculture in the last 50 years or so, and much of that is wrong or badly skewed. White Wolf's Changeling games for example make the bean sidhe incorporeal beings who attack to drain the life force from their victims. The Banshee from the TV show Charmed are witches who become monsters through great sorrow and kill with their wail. Mercedes Lackey's SERRAted Edge series made bean sidhe into 'bane sidhe', explained as 'death of elves', a wraithlike creature who fed on life forces and killed with its cry. In most of these confusions the different concepts of the folkloric bean sidhe are taken and blended then added to for plot purposes creating something close to but very different from the folklore.
What They Aren't: Despite growing claims to the contrary there are no male bean sidhe, nor could there be simply by the nature of the term. A male would be a fear sidhe, an Otherworldly man. If it identifies as male its not a bean sidhe.
Bean sidhe also don't attack or cause harm with their voice, Marvel comic characters and popculture to the contrary.
Its probably also worth noting that while the bean sidhe can be an omen of death they are not general death omens and are always associated with specific families they follow. Unlike, say, Mothman, they do not appear before disasters or warn of major coming events; they are strictly indicators of an impending death within a family they follow.