Adult Monarch Butterflies winter in California and Mexico. In the spring, these adults migrate north, laying eggs and eventually dying. The caterpillars that hatch from these eggs eat only Milkweed. Eventually the caterpillars form a chrysalis from which an adult butterfly emerges. During the summer the cycle of adult butterflies progressing moving further north continues. During the fall, the last cycle of adult butterflies migrate potentially thousands of miles back to their winter grounds. It is not fully understood how these migrating butterflies know how to get to their wintering ground without having been born there. In 2024 the US Fish & Wildlife service proposed they be listed as threatened under the Endangered Species Act.
