Milkweed Tiger Moth

"Early instars appear slightly 'hairy' and gray. They skeletonize whole leaves gregariously, leaving lacy leaf remnants. They are gregarious until their third instar. Later instars sport tufts of black, white and orange (sometimes yellow) setae. The head capsule is black. The later instars wander much more, and may appear alone or in groups of 2-10. Mature caterpillars occur from June onwards (Wagner 2005). Larvae grow as long as 35 mm." ~wiki