Elementals Mimic Life.

Life, above all else, flows. It changes and moves and does all sort of other things. But it flows. In the late fall as winter snap around the corner it flows from the north to the south. In spring, it flows in the opposite direction.
This flow is incredibly powerful. Geese fly through hurricanes, fish leap up water falls, gazelle cross hundreds of miles of predator-strewn savannah. It is little wonder that at some point the elementals themselves became tied to it.
Some of the smallest elementals, completely without any degree of self awareness, but surprisingly powerful for it.
These creatures mimic life though they are not of it, going so far as to experience 'death' and 'birth', and needing to feed.
They are called motes.


Fire
False Souls-These motes, like all others, are not normally visible to the human eye, only those trained to see them, or possessing of some natural gift which allows it are able to percieve them. However these motes are different in that they enter a stage of their lifecycles in which they are clearly visible to all people. In their natural state they appear as floating balls of vapor, or flame. Eventually however they chose an area to nest in. They settle down and spread themselves in a fine mesh dozens of meteres across. Within this area they are slowly pulled into component fiberes and strings bycreatures passing through. Once in contact with flesh, the strings will burrow within the host, leaving behind a sharp burning sensation. Slightly painful, but harmless.
The trouble often does not come for many years later. If one of the infected hosts gives birth, the child will not mentally develop beyond that of a toddler. It's lifespan depends on it's species. However once it reaches a certain age, approximately thirteen in humans, the body simply stops, before literally exploding into dozens of False Souls, revealing the simple minded child for what it really was: A construct of developing False Soul pupa, using a stolen form from it's host.


Earth
Messenger Sprites- Tiny creatures which look a bit like a shell-less crab, perhaps half an inch across. They live in small, enclosed spaces, and there emit a fine web which coats every available surface.
From there they draw nourishment directly from the surface. Mostly notable because they cannot long survive outside enclosed spaces, and if their home is suddenly opened up they will quickly retreat into the Plane of Earth, bringing their surroundings with them. Usually including the incautious soul who disturbed their resting place. However if the walls are instead slowly made less firm, the creature remains calm long enough to handle. The classic example is to find one in a certain type of silk coccoon (specifically one made with 2 or more threads, as opposed to the usual single string). Slowly unspin the two threads into two seperate, hollow spheres of silk, and the Sprite will remain calm for a time.
Interestingly if deposited in an enclosed space composed of PART of it's original home (like say one of the two silk spheres) then it will freely travel between it and the other sphere (provided of course that is ALSO an enclosed space) as it regards them both (connected through the shortest possible path in the Earth Plane) as a single space.
In this way they can be used as messengers. A sealed hole in one cocoon can be briefly opened, and the fleeing sprite drags a message held nearby with it as it flees to the other portion of it's home.
If the cocoons are identical, then the message should appear within the other cocoon within seconds, regardless of distance, ready to be pulled out of the hole.


Air

Muu-appearing as small snails these motes devour sound, but at the same time are fearful of overmuch noise. As such they tend to avoid developed areas, but instead gather thickly around sleepy little hamlets.
They are most active during the night, and for most part are harmless. However large infestations of them have occasionally caused all sound in the area to be consumed, resulting in absolute, utter silence for miles in every direction, driving men mad

Water

Blinders- Among the smallest and most powerful devour, each smaller than a mote of dust, these creatures eat light, but are easily killed by the heat of direct sunlight. As such colonies appear as a jet black fog or cloud, most commonly within deep forests, or at sunrise and twilight. Normally harmless to humans, overlong exposure can result in problems. It's possible a single Blinder may make it's way into the ocular cavity.There it will breed, and it's offspring will grow within the eye, eventually blocking out all sight, causing blindness, as all light reaching the eye is consumed before striking the rear wall of the eye. At this point the host must keep the eye closed for the rest of his life, else they shall continue to feed upon the light and breed, eventually building up pressure within the eye and damaging it.
Keeping the eye closed for long periods of time may begin to starve the creatures. This can be recognized by painful, black tears as the dead bodies seep out of the eye.
Those who become lost within a Blinder colony occasionally report seeing a brilliant light in the far distance. Non one who has walked towards that light has ever returned.

I like these magical chinchillas. My only problem with them is that I don't see a whole lot of use in them. I mean, certainly, it's useful to flesh out the world, but you don't really say just what kind of presence they have.

In my eyes, they are either everywhere, or they're barely there at all. The problem with the former is, in the case with the earth ones, by now everyone will have something akin to the internet. If it's the latter, then they aren't really around so much. That's no so much of a problem, but then they'd be rather useless roleplaying/world-wise other than fluff. Fluff is always good, but I just want to know what kind of presence you think these would have.

the rarity varies by specific species. They aren't limited to these stripes, these being more by way of example. I have a few ideas about some of the more complex structures they form (one of my favorites is actually a colony of both water-based motes and earth-based motes, that has the effect of a 'travelling swamp'. There one evening, gone the next, travelling and surfacing through underground tunnels and rivers.)

As a whole, motes are more or less omni-present, with perhaps significantly fewer in heavily developed human settlements. Individual species however are sharply limited by area and geography. Honestly I suggest treating them like insects. They're everywhere and you're never going to find anywhere completely devoid of them, but you won't find every species everywhere, and they might act completely differently in different places.

As for people exploiting them:
Only one in a thousand people can perceive them without special training to do just that, they can't be trained to any degree.
Further they're barely aware of human existence, let alone caring about it directly. Most of the ones with the most startling or actually useful powers, are also the ones that are very dangerous to handle.
The messenger ones for example. Lets say you keep a messenger sprite in a specially made box.
Now lets say one evening as you prepare to send a note (to the single other location the sprite may take it to) you drop the box.

Now immediately you have to ask yourself one question.
Is there an open door or window in this room? Cause if there is, the messenger sprite will immediately flee to the Earth Plane. Dragging you with it, where you will spend the rest of your incredibly short life wishing the Earth Plane contained some air.

If there isn't then the same thing happens, only it's now delayed until a door or window is opened. If you are VERY lucky, you might be able to avoid startling the little bastard into running away, and make a new enclosed space around it and thus survive.

Motes are small, motes rarely interfere with human life, motes can't be trained, motes, in general can only rarely be seen at all.

They are not malign, vicious or directly powerful.
But they are dangerous. Letting those who haven't made a long-term study handle or try to exploit motes is like letting a child play with powertools. Sooner or later it will end in tears.

The chinchillas seem to be quite dangerous, but if they are as rare as you say, they may be the cause of life's everyday aches and pains. And aging being painful is perhaps majorly contributed to by them.

That said, even if people can't see them, I must believe that a mother would notice their child pop, or peel open...