\" \" Danaus plexippus) on a milkweed plant. Fish and Wildlife Service ( CC BY 2.0 A monarch butterfly () on a milkweed plant. Take the monarch butterfly (Danaus plexippus): The North American population has tanked in the past 20 years, dropping by around 80 percent since the turn of the millenium. There are lots of different types of milkweed that grow in a variety of soils. Now That's Interesting You can order monarch butterflies through the mail and grow them in your home.