Put some air holes in the plastic wrap so the caterpillars can breathe. I usually cover the top with a piece of cheesecloth or really any kind of cloth. Also, you need to keep the milkweed fresh for them to eat and they eat a lot for a couple of weeks. I use a small jar from baby food filled with water to hold the milkweed. It will keep it fresh for several days or until it's eaten up. This way you won't need to keep picking more milkweed once or twice a day. Good luck and God bless you for helping the monarchs!

Yes, I did put airholes, but I have cloth and will remedy that today. I also have a small jar to put the stems of milkweed in. Thank you so much for your input.