‘Fairy’ is a word that has been evacuated of much of its original meaning in everyday language, for a variety of complex cultural reasons. Yet just a century ago, in much of northwestern Europe (and beyond), fairies and their regional variants were so intensely feared in rural societies that this terror directed everyday behaviour in large and small ways. For example, in early twentieth-century Ireland even something as small as throwing dishwater out of the window was taboo, in case the water landed on passing fairies and offended them. Any talk of the fairies was laced with euphemism and circumlocution, and actively discouraged; even to mention the ‘fair folk’, the ‘good people’ or the ‘good neighbours’ was to tempt ill luck from them.

The association between fairies and luck is basic: the English word ‘fairy’, from French fée, comes ultimately from the Latin fatum, ‘fate’. Just as in Classical literature fate is an amoral force, without compunction or compassion, so fairies are ministers of fortune good and ill and, like luck itself, terrifying in their moral ambiguity – moreso, perhaps, than beings of pure evil. Fairies embody uncertainty and unpredictability; they lurk at the disordered fringes of what is apparently ordered society, probing the weaknesses of human illusions of security. It is surely no accident that one of the most persistent beliefs about fairies is that they are prone to stealing human children – for what purpose is never clear – since there is no greater fear for a parent than losing a child.

When we look closely at traditional folklore about the fairies, the claims made about these entities are mind-bendingly odd – so much so that it is very difficult to define a fairy in any satisfactory way, even when we only consider the folklore of one country, such as England. The fairies are sometimes barely distinguishable from human beings; at other times they are tiny, or monstrous. Sometimes they are solitary; at other times they seem to embody an entire alternative society, with its own rulers and laws. Sometimes the fairies are benevolent; but at other times they are capricious and even downright evil, eager to take revenge and meting out disproportionate punishment for trivial offences. Sometimes the fairies seem to share our world with us, but at other times they are dwellers in an alien realm, often hidden beneath the ground or within hills and barrows. And sometimes the fairies occupy the same time as us, but at other times they seem to belong to an entirely different temporal continuum, where a few hours turns out to be centuries of human time.

There have been many attempts to categorise fairies neatly and squeeze them within a coherent cosmology. In medieval and early modern Europe, some theologians denounced fairies as straightforward ministers of evil – demons sent from hell to deceive the ignorant and simple. Others tried to account for the moral ambiguity of fairies by arguing for their situation somewhere between angels and demons; angels expelled from heaven who were not so evil as to fall all the way to hell, and who therefore remained on earth to wander among mortals. Yet popular belief in fairies rarely if ever conformed to scholarly prejudice, and fairies remained an unstable ontological category that defied easy incorporation into Christian cosmologies.

The association between fairies and the earth is so frequent in the folklore of Britain and Ireland that it seems almost a defining feature of them, leading some folklorists to suggest that fairies are ‘chthonic’ entities. In Ireland, famously, the fairies are known as the aes sídhe, ‘people of the mounds’, a reference to the Neolithic and Bronze Age burial mounds (barrows and passage tombs) that litter the Irish landscape. Similarly, in Scottish Gaelic folklore the fairies are the equivalent daoine sìth. Tales from medieval England feature mysterious individuals who feast inside barrows or emerge from them to offer drink to the passing traveller. Yet it is not just mounds that were associated with otherworld entities, but also gaps in the earth – like the wolf-pits in which the villagers of Woolpit in Suffolk (a village whose name derived from the pits) found a boy and a girl with vivid green skin in the twelfth century. The green boy died, but the girl survived and eventually lost her green tinge, later describing how the pair became lost in their own country and found themselves wandering through tunnels where they heard bells and eventually emerged into the daylight of our world.

One possible explanation for the chthonic nature of fairies – their association with the ground – is that they are the dead. While ghosts belong to an essentially Christian way of imagining an attenuated existence after death – a wandering soul, separated from its body, and an incomplete person which does not properly belong to the material world – fairies seem to embody a much older and more materialistic view of the afterlife. In the earliest stories of strange people dwelling in mounds, the fairies (if they can be so called at this stage) enjoy eating and drinking – a trait that brings to mind the burial practices of Europe’s pagan ancestors, who often gave the deceased the things they needed to enjoy the next life. If the fairies are the ancestors, they occupy (or at least partially occupy) a reality different from ours, but they are no less material than us. They are physical beings, not spectres. If it is true that the fairies are the ancestors, then this represents the survival, not only of pagan but of prehistoric belief into the Christian era. But it is also possible that the association of fairies with the ground and with barrows developed independently in the early Middle Ages; we simply do not know.

Fairies are inhabitants of an otherworld not only because they dwell below the ground, but also because they apparently exist in a different temporal continuum. The story of the ancient British King Herla, recorded by the medieval author Walter Map, is one of the earliest examples of this theme. Herla is visited at his wedding by the king of a strange people, a pygmy covered with hair who has hooves like a goat. The pygmy king bestows great gifts on Herla on condition that he comes to his own wedding in his kingdom in a year and a day’s time. Herla and his retinue therefore travel into an underground land lit by lamps and feast with the fairies for what they think is three days. At the end of their sojourn the pygmy king gives Herla a small bloodhound which will ride on his saddle, warning Herla not to dismount until the dog descends from its place. Herla and his companions return to our world, where they are puzzled to encounter a peasant who speaks a language they cannot understand. They eventually gather that three centuries have passed, and that the Anglo-Saxons have taken over from the Britons. Some of the retainers make the mistake of dismounting and crumble to dust, while Herla remains on his steed. Since the little dog has never jumped down, Herla is condemned to ride forever.

Many people today have a notion that fairies are significantly smaller than human beings, but in British and Irish folk tradition their size varies enormously. Indeed, fairies are defined in tradition not so much by their small size as by their variable one. They are not bound by fixed physical proportions, and when they are said to be smaller than people, this may sometimes be a symbolic marker of otherness rather than an indication that they inhabit a smaller world. The smallness of some fairies – who are most often said to be the size of children – is an eldritch quality that unsettles our established notions of age, maturity and strength. The idea of fairies almost as small as insects, prevalent in contemporary culture, seems to have been an invention of the seventeenth-century poet Robert Herrick, while fairies’ acquisition of wings was very late indeed in the history of fairy belief and did not gain widespread currency until the twentieth century.

The word ‘fairy’ is a fourteenth-century Middle English coinage; before that, the fairies were rarely given a consistent name; sometimes they are not named at all. The fairy-stolen child Malekin, whose spirit manifested as a poltergeist-like entity in a castle in twelfth-century Suffolk, spoke simply of ‘others’ who took her while she lay asleep in a field as her parents were gathering in the harvest. Malekin has been among the ‘others’ for seven years, but like King Herla she has not aged and still speaks and acts like a one year-old child. In the north of England, especially, the fairies were often called elves – an inheritance of Anglo-Saxon belief, where elf seems to have been a synonym for ‘demon’ and referred specifically to sinister entities who caused sudden pain and death in people and animals with invisible ‘elf-shot’.

Perhaps the greatest burden the fairies carry, which makes it very difficult for us to approach them with honesty, is the names we confer on them. As soon as they are named (whether as fairies, elves, piskies, trolls, etc.), we are tempted to stereotype them. The tendency to stereotype fairies, and divide them into ‘types’, may have a lot to do with the fact that their fluidity and unpredictability disturbs us. We do everything we can to try to apprehend the fairy realm. Yet in reality, when we look closely at traditional folklore, the distinctions we try to make turn out to be ephemeral or vanish altogether. Fairies are chthonic, interdimensional otherworlders who can enter our world, but who are not bound by its rules in the same way we are.

The point has frequently been made that the fairies of modern mythology are extraterrestrials, insofar as aliens seem to occupy the same niche in the collective cultural psyche once occupied by fairies. However, it is noteworthy that the otherworlders of the past came not from the stars, but from under the earth (although, remarkably, it was suggested as early as the 1620s that the Green Children of Woolpit were visitors from another planet). The same fantasies of abduction and return seem to attach themselves to extraterrestrials and fairies. Yet the idea of threatening otherworld beings from above is distinctly modern: before the dwindling of monotheistic belief, any being from above would have been an angel, and so the morally ambivalent fairies must dwell, by definition, below ground. Unlike aliens, however, fairies do not unsettle us by being completely other; rather, they do so by being not quite human. The horror of fairies comes closer to that of the doppelganger than the monstrously alien, and fairies arguably have more in common with visitors from parallel universes than with extraterrestrials. If we choose to use the language of science fiction instead of folklore, the fairies are interdimensional entities who transgress the boundaries between different continuums of space and time.

Our understanding of fairy belief – and, in particular, our ability to grasp why people took it so seriously – can be hampered by the folkloric garb and language in which our imaginations and culture shroud them. We relentlessly categorise them as entities that belong to folklore and, therefore, to the past. The usefulness of experimenting with alternative language to describe fairy encounters – language not particularly associated with folklore, such as that of science fiction – is that it allows us to explore the terrifying potential depth of fairy belief and why it proved so resilient and so fear-engendering from Ireland to Iceland until very recent times. Forget aliens, ghosts and monsters: is there really anything more terrifying than the almost human?