When the caterpillar is full grown it usually leaves the milkweed plant. It crawls (sometimes 20 or 30 feet away from the milkweed) until it finds a safe place to pupate.
The caterpillar lays down a silk-like mat and then attaches itself to the mat with its cremaster. The caterpillar allows itself to drop and then hangs there, upside down in a J-shape, for about one full day.
The caterpillar’s skin is shed for the last time as it passes from the larval (caterpillar) stage to the pupa (chrysalis) stage of metamorphosis. Under the caterpillar’s skin this time is a jade green casing which is called a chrysalis.
Inside the chrysalis, which is only about an inch long, the caterpillar will miraculously transform into a beautiful butterfly.