I gave up long ago trying to actually see spider mites. They are just too small for my eyes. They can be in a photo, and just not be noticeable too. So instead, I learned to recognize possible mite damage and when I see it, I treat all the plants in that immediate vicinity for mites. If one plant shows symptoms, it is almost certain that many plants have at least a moderate infestation. If you don't treat all the neighbors too, a day later more mites move back onto the weak tree.
Use a pesticide labelled for mites, if the label does not list mites, false, flat, red, true, and 2 spot spider mites are all possible causes. If the label doesn't list mites it probably won't kill mites. I use Pentac WP, but any miticide can work. The "non-toxic" sprays like Safer's Soap only work if repeat applications are followed at the label recommended frequency.
Definitely treat for mites, it won't hurt. Be gentle spraying those leaves, they look fragile.