Another thing that's different than most caterpillars that I see is these make small, subtle webs around the ends of the branches. They don't stand out and I wouldn't have noticed them except they were around head level to me. Only the branch on the right (also seen in photos #1 & #2) is occupied by caterpillars. All others had silk on them but no larvae. They had been defoliated and my guess is the caterpillars had moved on.