Question
Two days ago, I noticed the leaves on our oak tree were wilting and discolored.  I attributed this to the ongoing drought and watered more around the base of the tree.  At that time, there were no other visible problems with the tree.  This evening we noticed webs wrapped around about 60% of the tree.  They are not wrapped around the branches and leaves like webworms and there are tiny insects actively moving around the inside of the webs that are about 1/10 of a centimeter.  The back ends (abdomens) appear to be about twice the size of the middle (thorax) and they are not ants or worms.

They are obviously very fast moving.  We have 2 oak trees right next to eachother (6 feet apart)that do not touch and at this point it is only in one of them.

What are these and how do we treat them?

Answer
Stacy,

Sounds like it could be spider mites. See http://www.livingwithbugs.com/spider_mites.html for general info about spider mites. Some species can produce large amounts of webbing especially when leaves are dry. Unfortunately there's not much you can do about spider mites in large trees except give them extra water. They will probably survive but it may take a year or more to recover lost growth. Post a follow up if you have questions.

Jack DeAngelis