Question
In mid October we had thousands of tiny green worms coming down on webs or strands out of our giant oak tree. They then formed tiny white pupates stuck to and tucked into just everything. We had a similar event at least 5 years ago. I do not remember any damage to any other vegetation the next year except the pupates are stuck on everything. Should I be concerned about the health of the oak? Should I worry about any other damage when these pupates hatch? Will the winter kill the pupates? The tree has lost at least half the leaves already...way ahead of the maples. We are on the west coast of Michigan.

Answer
Jo,

These are probably caterpillars of one of the oak looper moths. Oak loopers can do considerable damage to oak leaves but usually trees recover unless defoliation occurs several years in a row. You are correct that the larvae that drop from the tree pupate after they reach the ground. They won't cause any damage but will emerge as moths next spring/summer and probably re-infest the same trees. These moths have many natural enemies so there may be fewer next year. If the oak tree is already in decline for some reason the oak loopers can further injure it. Unfortunately there's not much you can do to treat a large tree like this one.

I hope this is useful.

Jack DeAngelis
http://www.livingwithbugs.com