Throughout their development, almost all butterfly caterpillars remain on the plant where their eggs were laid, or move only short distances to feed on other suitable host plants. Larger, more visible caterpillars also may display characteristics designed to protect them from birds and other enemies. Monarch larvae feed heavily on milkweed and accumulate toxins called cardiac glycosides in their wings and bodies. The bright and distinctive markings of these colorful butterflies tell potential predators that their taste is bitter and the predator would be better off leaving them alone. Predators quickly learn this message.
Caterpillars shed their skins four or five times as they grow, in a process called molting.
You may notice their shed skins on the host plant. After the caterpillar has molted a predetermined number of times, it wanders from the feeding site and searches for a place to dangle from and pupate. After attaching its posterior end to an object, the caterpillar molts again, revealing a different skin, which hardens into a pupa. It reorganizes its body plan inside the pupa, called a chrysalis, then emerges as a butterfly. Generally, butterflies that overwinter in Minnesota do so in the pupal stage and emerge in spring as adult butterflies.