Milkweeds are the favorite food of Monarch caterpillars and the nectar of the flowers is prized by many types of butterflies so it is a good choice to plant in a butterfly garden.
The female Monarch lays eggs on the undersides of the Asclepias leaves and they hatch into tiny larva. All they do is eat and eat and eat, eventually becoming 2 or 3 inches long. Then the caterpillars lumber off to a protected area where they attach themselves and spin a cocoon, or chrysalis, covering around their bodies.
This picture was taken by our friend Penny Livingstone. The chrysalis were in her greenhouse. The one on the right is about to hatch; you can see the butterfly wings inside the cocoon.