The lethfly is one of the few non-sentient fae species. Being non-sentient, it is automatically unseelie, as only sentient species can join the Seelie Court.
The etymology of the name is disputed. Some trace it back to Old Swedish “leþ” + “flugha”, with the latter meaning “fly” and the former meaning “journey, way, manner”. Others claim the “leth” comes from the Greek “lethe”, meaning “forgetfulness”, but it’s less clear under this explanation how “fly” ended up tacked on the end.
A lethfly is a tiny lepidopteran, about 30mm in size. The females have pure white wings, while the males’ wings are outlined in a thin blue rim while otherwise being pure white. In both cases, the white scales are highly reflective, causing them to appear to sparkle while in flight.
The lethflies mix features of butterflies and moths. Due to the wings, many would call them a butterfly, though unlike true butterflies their upper and lower wings are linked together. Their bodies are also shorter and fatter than those of a typical butterfly, yet not hairy like that of a moth. The antennae bear a small club at the tip, like those of a butterfly.
Like more mundane insects, a lethfly begins life as a larva – a leaf-green caterpillar no more than 12mm in length, bearing many long white hairs along its body. The lethfly caterpillar is often mistaken for that of certain plume moth species.
When it comes time to transform, around 4-6 weeks after hatching, the caterpillar forms a chrysalis rather than a cocoon. The chrysalis is blue in colour, and fixed to a twig or stem with a wad of silk. The lethfly emerges from its chrysalis about two weeks later.
Lethflies mate and lay eggs the same as other lepidopterans. In temperate climates, they can breed twice per year, with new hatchlings emerging in late spring, developing to maturity over the next two months, and then mating and laying eggs which incubate for six to eight days before hatching out to repeat the cycle. This time, however, the weather is starting to get cold by the time the eggs are laid, so they won’t hatch until the following sprint. In warmer climates, however, lethflies can breed all year round, with four or five flights each year.
Adult lethflies can live up to eight months in warmer climates, though in more temperate climates they would be killed off by the winter frost by they time they reach half this age.
Lethflies feed on memory, especially long-forgotten memories, memories attached to places, or memories of the dead. A lethfly can gain sustenance from any place where humans (or other sapient species) have once lived within the past ten to twenty years; any longer, and the memories fade. A lethfly can also gain sustenance from the memories of living sentient creatures.
A lone lethfly is harmless, as the tiny quantity of memory it can consume will have no discernible effect on a human. You’d forget something, sure, but it’s the sort of thing that you very well might have forgotten anyway – for example, a phone number you were trying to keep in your head while you dialled it.
However, in greater numbers they can rob a human of significant portions of their memory, starting with short-term memories but, if permitted, eventually working through longer-term memories as well.
Lethflies are also poisonous. Their body contains a potent poison that can kill small birds within minutes. Fortunately, a human is unlikely to die from the poison, but it can be absorbed through the skin and produces an intense stinging sensation, similar to nettles.
Society and Culture
Lethflies are not intelligent and thus do not have anything that could be called culture. They are social insects, however – they commonly travel in swarms of hundreds of individuals. Usually, lethflies avoid humans, preferring to settle in desolate buildings or cemetaries, whre there is an abundance of memory remnants. However, if disturbed, or if they detect one of their number has died, they will swarm the culprit. Usually, such victims don’t even remember what happened.
Lethflies commonly gather around fresh graves, usually early on the morning after the burial. This represents a feast for them, so they can be seen in especially great numbers. However, they do not gorge for long, and as a result there are actually not that many sightings of this practice.