It sounds like you have a little critter called a spider mite. Unfortunately since they are mites, not true insects, a lot of insecticides will not work. You will need to look for a miticide. They are easily found in most garden supply stores. Follow the directions on the label, and you may need to do a reapplication to control the eggs that have not hatched yet, a few weeks after the initial spraying.
You may also want to quarantine these infected plants to ensure that the mites don't infest anything else
Good Luck
Mike

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