I've had the same thing on some of my plants. I noticed the plants were drying up and looking unhealthy, wilting, etc. Then I noticed very fine little strands of webbing in a few areas, which was only visible from certain angles. I used a bright LED flashlight (far better than the older types for clarity) and a magnifying glass and started looking very closely, and I discovered very very small insects moving around. I had to sort of look at them for a few seconds to see they were indeed moving. Or I would gently tap the leaf to see if they would move. It was hard to tell what color they were as they were so small, but they looked like a pale whiteish yellow. Even with a magnifying glass, I couldn't identify any features or shape to them - that's how small they were, like specks of dust - but they were definitely alive. Now, on another plant on a separate occasion I noticed no webbing, but there were hundreds of little yellow insects all huddled together on the underside of the leaves. These were much larger than the ones I described above, but still very small. I ended up discarding a few plants and the others I rinsed in the shower, sprayed with insecticidal soap and then examined again for signs of bugs with the LED light and magnifying glass, and they seemed clean. I kept checking them a few times a week and after a couple of weeks I noticed the bugs were starting to come back, so I repeated the shower/insecticidal soap procedure again. Eventually the plants recovered and I saw no more of the bugs. From everything I read online, I decided they were spider mites.. but as someone above said, maybe they were some other kind of mites. When this first started happening, one plant was VERY heavily infested with the larger yellow bugs I mentioned above, but had no webbing at all. These bugs were only on the undersides of the leaves and on the stem and in crevices. Another plant which had the very small nearly invisible bugs had only a few strands of webbing that was hard to see at first. These little bugs weren't just hiding in crevices and undersides of leaves - they were out in the open sometimes hanging from little strands of webbing. Yet another was so infested with the nearly invisible bugs that half the plant was cocooned in webbing. I discarded that one instantly in a state of horror.

I don't mean to alarm you...but it may be fumes from heating system or it may be just that the humidity is very low. I've had similar and noticed it coincided with use of the heating system last year. Since we don't run heat a whole lot down here, you can see the effects and know it. Our house has an unvented propane stove used primarily, and I blame it. I'm moving in two weeks...and hope my plants appreciate it (other reasons too of course).

Tiny aphid/shrimp sounds like thrips to me. They are nearly invisible but move fast when they are disturbed. Pictures on the internet often seem to show dark colours, but they appear very pale in my garden.

Oh Hobby....You should of see two winters ago!! I took sick for a week where my HUGE three feet tall Gardenia resided in a huge window which was amazing..Well, it so happens that that summer I broke my heel falling off a ladder doing roofing and I could not spray my plants like I would of with the F.E... I had no friends willing to offer besides no longer my friends.. Well, during the time of just that one week I was sick, I came back to work to be greeted with a huge gardenia that looked like it was sprayed with Halloween cob web which look like fog from a distance...Little did I expect to see those dam critter, mites having a huge party crawling over the place! Do you know that I had no choice but to lift that thing over my head to the dumpster in which all those mites just fell all over me! It was disgusting..I had to strip naked when I got home outside in 30 degree weather and take a shower just to make sure I did not carry just one of those things into my house..I'm sure that one would of devastated my collection..I always had a fear of mites. always...That is why I am so careful to avoid them! I hate them..I watch all my plants all winter long looking for just one..I can usually tell when I have them, I am that good and know them that well..I can tell the damage a mile away....My 'Rosemary' Oil will always be in hand if I ever have any again.....They will never get a hold of my trees, ever... That is also the reason whey I stick them on my cold porch..No pest survives or forages in temps that cool, especially after spraying the leaves with mist, cool and a fan going...Not one bug ever..I would rather sacrifice extensive growth than deal with bugs..I almost threw away every plant I owned because It too much work to keep up..The spraying inside can be such a pain...My gardenia plants, spider mite magnets get sprayed every week no matter what, because they are kept warm inside or in my greenhouse..Don't need then attracting any for sure) Wow, you opened a can of worms with me, or should I say MITES..lol