The Monarch, indigenous to the New World, occurs throughout North and South America. It also has established breeding populations in Australia, a number of Atlantic and Pacific Islands including Hawaii and Bermuda, and the eastern coast of Spain.

Monarchs lay their eggs on milkweed plants (genus Asclepius). The caterpillars that hatch from the eggs feed on the milkweed leaves, incorporating the plant's toxic compounds (cardiac glycocides) into their bodies. As the caterpillars grow, they become more and more distasteful to potential predators. They usually pupate near the plants on which they feed. When the Monarchs emerge as adults, they either continue migrating to the north and east or turn around and start the journey back to their overwintering grounds, depending upon the time of year.