As caterpillars, monarchs munch on milkweed. That diet would sicken or even kill most animals; the plants produce cardiac glycosides, which disable the sodium pumps that cells use to regulate salt levels. For organisms with hearts, this can result in cardiac arrest. But monarchs never digest the toxins. Instead, in a process called sequestration, they carry the cardiac glycosides inside their bodies as they create cocoons, mature into butterflies, and take flight. Milkweed plants have evolved toxicity precisely so most insects won't eat them, so being able to absorb their power gives the orange butterflies—along with about 20 other types of insects—access to a food source without much competition. It also renders them toxic to would-be predators.