We used to get lots of caterpillars on the milkweed, and see plenty of bflies laying on them, but lately no big 'pillars. But the boys usually manage to find a few tiny tiny larvae and feed them till they hatch out.
I think that the ants and earwigs eat all of the baby caterpillars, and they only survive if we find them when they are just hatched out.
It is so easy and fun, watching them chrysalize (or whatever its called!), and then watching the chrysalis change color days before it hatches out.
I've noticed plenty of them migrating already for the last few weeks. They got to go a long ways, and they don't go too fast either.