It is taking its toll on the plants. The plants have been trying to regenerate, but before they can generate enough leafage to gain some strength, they are eaten back and forced to start all over again. As they try to recover time after time, you can just see them slowly give up and die. Before the caterpillar explosion, they were recovering from a severe aphid outbreak. The Ladybugs eventually got most of them, but they took their sweet time.
Milkweed has a tough life for a poisonous plant.
Obviously, larva are present. We see more of them at this time of year than during the summer. In late summer, you may not see a Monarch at all. However, when they come down for the holidays, as they always do, they make pigs of themselves. Well, many of the caterpillars did make it through to chrysalis despite the current drought of leafage.