Most of the summer, I only had about 4-5 monarch caterpillars. This past week, There are 6 on my milkweed-eating well and very plump. But the milkweed is starting to die off. Plus the evenings are getting cooler. I didn't find any definitive information regarding what temperatures they can endure or, what happens when the milkweed supply is gone. They're pretty large and plump now, but it seems like there may not be enough time for them to make a chrysalis , and then migrate. Bev Propen