The brown/red mites I've seen are pretty tiny. I get these really fast moving mites that are about the size of the image below (used just for reference, species unknown). Even the larger, slow moving ones are only in the 0.5 - 1.0 mm range.

Andrew

I've seen three in my bins and I do belive they are all mites.

White mites - the largest of the three, hardly ever move.
Red/brown mites - mid sized, they do move around, almost constantly but never really fast.
Tiny brown mites - very small, almost invisable, very fast.

Page with pics of the first two, descriptions of the three.
http://www.redwormcomposting.com/worm-composting/a-mite-is-a-mite-is-a-mite-not-quite/

Hard to say sure as no pick of the tiny one (never found a pic anywhere), but I've only see these three types in my bin. Shouldn't be a problem, if anything according to the description it should be a good thing.

The smallest mites I've ever encountered are grain mites. I once had an infestation in my mealworm and superworm tub. They were SO tiny that you will not notice their presence if not for their out of control population! I had to stare at the sides of my tub real hard to notice those moving dusts! There are many different kind of mites, I'm not sure if you can have grain mites infestation in a vermicompost bin though. But when you mentioned they're super tiny I immediately think of those horrible grain mites.

Are grain mites bad? I do have to really look to see them.

The red/spider mites are the ones you don't want - they suck the blood not only from your worms but from the capsules as well, and an infestation can potentially wipe out your worm population unless addressed - generally mites appear when the bedding is too moist and the PH too acidic, and in that environment, the worms aren't happy either.