I wonder about using a hair dryer for reducing humidity on a cactus and killing mites?
I take back my suggestion of a hand lens if you have the kind of mites I have.
Last night I couldn't take it any longer and dug out my old dissecting microscope. 10x and 30x stereoscope. The first thing I saw under 30x was how amazing the spines and areoles were!!! I have some cacti that were suspected mite victims and I put them under the lens - and there they were. Zillions of them. And they are tiny. There was no webbing and these are definitely not red spider mites. Maybe some form of two-spotted mite, but very small. I took very primitive pictures with my cheapo Canon 540 camera and just held it to the eyepiece set on automatic. Not great pics, but I think instructive. I'll try for better.
I used Rebutia narvaesensis which is pretty small - about 1/2 inch diameter. Here it is with the microscope to get perspective. Note the tiny size of the spines.
And here is the apex at 30x - the only part of the plant still green. Sorry for the focus, the mites are the small fuzzy things towards the bottom of the growing tip and just below it, not to be confused with the grains of sand.
Here is another small cactus - not even sure what it is. The skin is completely white and not a web or mite to be seen with the naked eye. Note the size next to the pen point and especially the thickness of the radial spine.
And here is the same at 30x magnification. The mites are on the spines and about as thick as the tiny spines.
No wonder they could not be seen with the naked eye or even at 10x. A number of them are around the base of the spines and one is on the spine to the right. Another is on the end of a spine to the right and I saw this behavior very clearly - they would crawl to the of a spine and wave their legs as if looking for a ride. That is exactly what ticks do when they are looking for a host to latch on to. I suggest if one has a plant or so with mites that they wash hands well after handling the plants - otherwise they may an unwitting vector to spread to other plants.
I splashed the plant with alcohol and was happy to see lots of dead dessicated mites and only saw one that was still alive after the alcohol evaporated.(from the end of a spine where the alcohol did not reach). Still working on this and I have to get better pics...
Amazing plants, amazing form, amazing flowers...