Monarch Caterpillars

The milkweed is disappearing with all these caterpillars around. I need to make sure to grab some seeds from the pods and get them into the ground so we have more for next year.

Some are forming chrysalis, and a couple have died before shedding their skin. Wonder what exactly happened (the ones that didn't make it weren't touched by human hand, so I am wondering if a disease or parasite may be the cause)...