Oh boy, story time. This was six years ago (and a machine translation of what I wrote back then).

My daughter doubts that the tooth fairy exists.

She mentioned this today on the way home from school. Then we had a little chat about how “believing in X” versus “X exists” relate to one-other.

I then asked if we could find out if the tooth fairy exists? We could, for example, set a trap: then we could see for ourselves! My daughter thought that was too cruel and anyway, imagine if something happened to the tooth fairy? All right, but we can make something that won’t harm the fairy … but no, she doesn’t want the fairy to get caught. Fine, then we can put the tooth on a plate of flour so we can see the tracks? No, because fairies can fly! Then maybe we can make a little “roof” so the tooth fairy has to land and crawl? Yes, that was accepted.

…But how big is such a tooth fairy really? I have to admit that I’ve never considered that … have you? I made a roof out of a plastic container, but Inara thought that a fairy is definitely smaller, so we settled for a corner of the roof - yes, now the fairy can’t fly under!

I’ve also talked to Inara about whether “no footprints” means “the tooth fairy doesn’t exist” and whether “footprints” means "the tooth fairy exists (or whether there might be fairies even if there are no footprints). So now we’re waiting anxiously to see if we can see any traces tomorrow! (Hint: yes, there are traces: you can see that the tooth fairy has been on her knees and tried to reach the tooth, but couldn’t. So there’s a small letter instead of a coin.)

Oh yes, how we lie to the coming generation… Forgive me, daughter!

The following day after school, she had brought a friend home and I casually asked if she’d checked on the trap? She had not! They both raced up to her room and I could hear the shouts of glee. They definitely believed in the tooth fairy! But also, my daughter was somewhat distraught and wrote an apology letter for having teased the fairy and ask for forgiveness. Such a sweet kiddo. Still is.

I’m answering this as a science question. If that wasn’t the point, my apologies.

Aerodynamics fix the wing to body ratio of a creature pretty tightly. If you want a wasp-like ratio, it’s going to be a wasp-sized creature. To reach ball-sized, they’re going to need to have eagle-size wings folded up around them, not cute little things on their back.

I guess for imagery sake, imagine you had a roommate that was one, so you have to take their size into account for things like cooking and cleaning.

An entire human-size dwelling would be very expensive taste for a pixie, even with a roommate. I think they could only be in charge of cleaning an area realistic for their size, but pretty much nothing else in the way of typical unskilled labour.

If something breaks they’d make a hell of a repair person, though, since they could reach all kinds of things inside a machine, and they’d be able to process food in ways that are just too picky for humans to bother with. The Inuit have a delicacy called mouse food, where lemmings collect the tiny edible bits of otherwise unpalatable arctic plants, and then they loot the burrows until there’s enough for a person.

Maybe an entire colony of pixies would be a more realistic co-occupant. I’d really worry about one of them peeping at me, though, since a tiny creature can hide anywhere. Safety would also be a concern; there’d have to be ground rules about what surfaces are to be ordinarily kept clear of anything or anyone that could be crushed, and regarding which containers I can handle and how.

Would they be able to lift/carry human-size objects?

No, they’d be able to lift around as much as a similar-sized flying animal. So, a little bit of pollen, a drop of fluid, maybe a small insect in a tiny cage.

Fairies - 15cm/6" Pixies - 5cm/2"

A fairy can wrap their arms around your wrist and you can carefully fit about three pixies in your mouth

I’m writing a book and pixies are the same size as everyone else. Thought it’d be neat lol.

So basically you’d like to know the theoretical lower limit for a miniature human, like a purse dog?

I would imagine a faerie to be 4–6” tall depending on age and gender. Take the height of a person in imperial measurement and cover feet to inches. And there you go.

I always thought a faerie chick would be a cool friend to have. Like a literally tiny punk grrl in your shirt pocket rocking out to a single AirPod just in your pocket, maybe she’s standing on it doing air guitar or something.

I’ve always imagined that they can change their size because 1) Fairies in British and Irish folklore were said to kidnap children , so they would need to be capable of overpowering them. And 2) Don’t a lot of stories or myths suggest humans, on rare occasions, breeding with Pixies? They can’t be tinkerbell-sized for that.

What chores? Everything that has to do with miniaturization. They’d have sub-millimeter fingers. Repairing that Iphone? The screw that I can’t even fucking see would be huge for them. Or as neurosurgeons, or or or

Biggest productivity win would be teams between humans, fairies and pixies. Each can do tasks according to his strength and size.

But wait. Maybe fairies are around, and they’re all locked up in sweat shops in Bangladesh or China producing new stuff to flood our markets…

I imagine a pixie to be roughly half the weight of two pixies, and double the height of a child pixie.

Or like 6-10 cm. They could train and ride rats into battle. And they absolutely would.

Fairies? Lower range of human size. Like your aunt who is super short but not like a medical condition. Fairies have a lot of medical conditions, though. Researchers speculate it is caused by inbreeding, but the fairies refuse.

I’d expect one to be about 6" tall, but I have yet to see one to confirm this.

They’d probably be covered in fur to reduce chances of freezing to death, something that small with that much surface area is going to lose heat at an extreme rate, and if they’re humanoid they need to metabolize to maintain body temperature.

The smallest ones are measured in nations. The largest ones are measured in light years.