The thing about spider mites is that they are not spiders. If you see webbing that is like a ‘classical’ spider web, you have a spider, which as was mentioned earlier is not a bad thing. A true spider will regard mites as an attractive dinner buffet.
Spider mites are generally on the more tender undersides of leaves. They get the ‘spider’ part of their name because they can produce a silk-like material, but if present it is usually a blurry, amorphous mess rather than an organized web.
Spider mites can also be almost too small to see easily. One way to detect is to hold a sheet of white paper under some branches and shake or jostle them—the mites will fall off and be visible.
They have a very short reproductive cycle, so whatever you use, do so every other day for at least a week. Neem oil works pretty well, but insecticidal soap is better [though it also kills predator mites, but those are not very common]. Using chemical insecticides or miticides can rather easily develop your own little resistant population because of the multiple reproductive forms present at one time.
I know that you have only a couple of trees or so, but generally for situations with multiple trees it’s always a good idea to isolate a tree with any sort of infestation while you’re dealing with it.