The Hunry Caterpillers
It has been a banner year for caterpillars (and consequently butterflies and moths!) Many species tend to be gregarious, as are these orange-striped oakworms.
Except in the case of young, small trees, their feeding does not harm a tree. Trees have many extra leaves--more than they need. And, this late in the growing season losing a few leaves will not hurt them.
If you can reach them, you can always put on some gloves and pull them off. Drop in a bucket of soapy water to drown.