I have gotten several pictures of orangestriped oakworms (Anisota senatoria) this week from homeowners and landscapers. I found a whole slew of them at a playground in Cary. While I was trying to snap pictures kids ran around stomping them (mine of course were gathering them up and putting them back on trees).
Orangestriped oakworm is a native caterpillar that live throughout the eastern and Midwestern US. They can defoliate trees in some cases but generally only a branch or two are affected. The main problem people report from these caterpillars is the mess of frass (poop) and bodies that litter porches and walkways beneath oak trees. Orangestriped oakworms have one generation per year. The adults are active midsummer and lay eggs on the underside of oak leaves. The caterpillars hatch and feed gregariously. The small caterpillars eat a little at first but soon get big. Large caterpillars consume entire leaves except for the midvein. They overwinter as pupae.
This time of year orangestriped oakworms are noticeable because they are very big (2 inches or more) and start coming down to the ground to pupate. Thus, by now they have caused all the damage they will cause for this year and no treatment will make a difference. Since the caterpillars feed in groups they usually defoliate one branch at a time. Therefore, if you see a group feeding you can prune that branch out and get rid of most of the caterpillars. There are a number of insecticides available to professionals for caterpillar control but generally these are not warranted since orangestriped oakworms rarely defoliate trees or negatively affect tree health. Though in natural and urban forests periodic outbreaks occur. Homeowners do not have many options for treating large trees. Pruning is the best way to reduce the amount of caterpillars and frass you have to deal with. As with most caterpillars these are great bird food and probably help plump up hungry birds as they prepare for a long journey south.