I found this unknown caterpillar in a small wetland in Philadelphia, PA along the Schuylkill River. It was on Phalaris, but I did not find any evidence of feeding. The wetland was dominated by Amaranthus, Phalaris, Typha, Scirpus, Nuphar, and Polygonum. The hairs on it are hard excluding the longest ones. It did not appear to be colonial.

I've looked through several books and the caterpillar pages and it seems to be a member of the Noctuoidae, though this is only a guess and I’ve found nothing that directly resembles it. I’m open to suggestion for id and further research.