Monarch butterflies are found across more than 90 countries, islands, and island groups worldwide, but their heartland is North America. Two distinct populations split along the Rocky Mountains: the eastern population breeds across the central and eastern United States and southern Canada, while the western population breeds across the western states. Beyond North America, monarchs have established permanent populations in Australia, New Zealand, parts of southern Europe, Central America, the Caribbean, and Hawaii.
The Two North American Populations
The Rocky Mountains act as a dividing line between North America’s two monarch populations, and each follows a completely different migration pattern. The eastern population is by far the larger of the two. These butterflies breed as far north as Ontario, Canada, spreading across the Great Plains, the Midwest, and the eastern seaboard during spring and summer. When fall arrives, they funnel south through several flyways that merge into a single corridor through central Texas, roughly following the Interstate 35 route through six states from Minnesota to the Mexican border.
The western population breeds across states like California, Oregon, Washington, Idaho, Utah, and parts of the southwestern U.S. Their range extends into southern British Columbia. This population is far smaller and has been in serious trouble: only about 12,260 monarchs were counted across 249 overwintering sites during late 2025, making it one of the three lowest counts ever recorded. For comparison, the 2020 count hit a rock-bottom 1,901 individuals.
Where They Spend the Winter
Eastern monarchs overwinter in a remarkably small area: 11 to 12 mountain sites in the states of Mexico and Michoacán, along Mexico’s Transvolcanic Range. They arrive in October and stay through late March, clustering by the millions in stands of oyamel fir trees at high elevation. These trees function as both a blanket and an umbrella, shielding the butterflies from freezing temperatures and heavy rain. Without this specific forest canopy, the butterflies would be exposed to lethal cold.
Western monarchs overwinter along the California coast, with key gathering sites near Santa Cruz and San Diego. They settle into eucalyptus, Monterey pine, and Monterey cypress groves, where the mild coastal climate and tree cover provide the conditions they need to survive winter in a state of semi-dormancy.
Year-Round Resident Populations
Not all monarchs migrate. Several populations have become permanent residents in warm climates where milkweed grows year-round. Southern Florida hosts a well-studied non-migratory population, as do Puerto Rico, Costa Rica, and Hawaii. These resident butterflies have actually developed different wing shapes compared to their migratory relatives. Migratory monarchs tend to have larger, more elongated wings suited for long-distance flight, while resident populations have rounder, smaller wings better adapted to short local trips.
These resident populations blur the line between the migratory monarch most people picture and a more tropical, stay-put lifestyle. In Florida, for example, monarchs breed continuously through the year rather than following the dramatic seasonal cycle of their northern cousins.
Monarchs Outside North America
Monarchs originated in the Americas, but they spread across the Pacific in the mid-1800s. Storms blowing out from New Caledonia carried butterflies to Australia and New Zealand, where they established breeding populations that persist today. These Australasian monarchs now face their own declines, likely driven by urban expansion eating into breeding habitat and the intensification of agriculture.
Monarchs also crossed the Atlantic, though more recently and in smaller numbers. Before any butterflies arrived in Europe or North Africa, two species of milkweed had already become established in the Iberian Peninsula and northern Africa. That meant monarchs blown off their North American migratory path by Atlantic storms could land in southern Spain or Portugal and find the host plants their caterpillars need. Small breeding populations now exist in these areas. Vagrant monarchs occasionally turn up on the coast of the United Kingdom, carried by strong westerly winds, though they haven’t established permanent colonies there.
Beyond these footholds, monarchs inhabit islands and territories scattered across the Caribbean, parts of Central and South America, and various Pacific islands. Their global spread happened in three waves: into South America, westward to Oceania and Australia, and east across the Atlantic.
What Habitats Monarchs Need
Regardless of where they live, monarchs depend on one thing: milkweed. Female monarchs lay their eggs exclusively on plants in the milkweed family, and caterpillars eat nothing else. The toxins in milkweed make both the caterpillars and adult butterflies unpalatable to most predators. In North America, over 100 native milkweed species grow across different regions, meaning monarchs can breed in prairies, meadows, roadsides, agricultural edges, and suburban gardens as long as milkweed is present.
Adults also need nectar-rich flowering plants to fuel their flights, especially during fall migration when they need to build up fat reserves for the winter. The combination of milkweed for breeding and diverse wildflowers for nectar defines a successful monarch habitat. Losses of both, particularly in the agricultural Midwest where herbicide use has reduced milkweed dramatically, are a major driver of population declines.
Conservation Status
The U.S. Fish and Wildlife Service proposed listing the monarch butterfly as a threatened species under the Endangered Species Act in December 2024, with a public comment period extended through May 2025. The monarch is not yet federally protected; protections would only take effect if a final rule is issued. The IUCN has already classified the migratory subspecies as endangered on its Red List.
The overwintering forests in Mexico face ongoing threats from legal and illegal logging, conversion of land to farming, and climate change. Rising temperatures and drought stress the oyamel fir trees that monarchs depend on, making them more vulnerable to insect damage and disease. In California, the western population’s overwintering groves face pressure from coastal development. And across the breeding range, the steady loss of milkweed in farmland and open spaces continues to shrink the habitat monarchs need to reproduce.