It's a looper...
Loopers get thier name from the looping motion they make when walking. There are a few different kinds. Did you find it on a hibiscus? I find cotton loopers(Anomis flava), on my hibiscus all the time in Florida. It could also be a hibiscus looper(Anomis mesogona), but I don't think they are found in the continental US. If you know the bushes were not exposed to any chemicals your chams will love them(mine do). They are probably very nutritious too since hibiscus leaves are very high in calcium. The caterpillars will fold a leaf in half and sew it together with silk and pupate inside, they turn into small moths.