The YEARS of folklore in Ireland regarding fairies and otherworldly beings is so much a part of the Irish culture that the University College of Dublin houses the National Folklore Collection and has a department called the UCD School of Irish, Celtic Studies, Irish Folklore, and Linguistics.
An evil fairy was often to blame for calamities. UCD Professor Ríonach uí Ógáin explains in his newest book, The Otherworld: Music and Song from Irish Tradition, that “Arguably these beliefs are one of the ways people try to rationalize what appears to be inexplicable to them.”
From the UCD site, “A calamity at sea or an untimely death might be explained by a curse or fairy abduction. Even a curious natural phenomenon such as a whirlwind might be blamed on the slua sí [fairy host] passing.”
So an evil fairy is only a manifestation of phenomenon that cannot be explained.