I am seeing droppings on my patio and driveway from what I think are from caterpillars in the oak trees in my yard. I can't seem to see the caterpillars, but the evidence is there. The trees are huge and mature and spraying is out of the question. What are the caterpillars called and what can I do about them? When will they go away? I don't see any leaves that have been chewed or webs. Strange.