I have two different kinds of milkweed growing in my yard that the monarchs have laid eggs on. My scientist friend says not to change the milkweed they grew up on. Luckily, only those four were on that particular kind. (There were more, but I think they were able to crawl away to form chrysalises before I bought the new plant). I still have about four or five caterpillars on the other kind of milkweed. And two formed chrysalises this morning, so they are safe.