Stories

The great monarch migration

A unique phenomenon under threat

The annual migration of the Eastern monarch butterfly might be one of nature’s most impressive feats. Each year, a “super generation” of monarchs flies up to nearly 3,000 miles from the northern United States and southern Canada (where they breed) all the way down to the Monarch Butterfly Biosphere Reserve in central Mexico (where they overwinter). The monarch’s migratory pattern is the most highly evolved of any known species of its kind.

Anderson Cooper and 60 Minutes visit the Monarch Butterfly Biosphere Reserve in Mexico
See the more from the 60 Minutes story on monarch butterflies

At winter’s end, these same butterflies fly an additional 600 miles north to the US where they lay eggs on milkweed plants. This marks the end of this generation’s unique eight-month life cycle. From there, successive generations—each living only three to five weeks—continue northward. The annual migration cycle concludes when the butterflies reach breeding sites in the northern US and southern Canada.

A monarch lands on a cluster of milkweed in the Northern Great Plains

Are monarchs at risk?

For two decades, WWF-Mexico, in coordination with local communities and partners, has assessed the population of the eastern migratory monarchs in the Monarch Butterfly Biosphere Reserve in Mexico—the only place where they congregate by the millions. Since it would be impossible to determine the population by counting every individual butterfly, the team measures the amount of forest area that is occupied by the monarchs, providing a scientifically robust indicator of their population status. The more forest that is occupied, the healthier the monarch population.

The most recent survey showed that eastern monarch butterfly populations nearly doubled from 2024-2025. According to the report, the monarch population wintering in central Mexico's forests occupied 4.42 acres, up from 2.22 acres during the previous winter.

While we have seen the monarch populations rise and fall slightly year over year, the eastern population of the monarch butterfly has been in a steady decline, on average, over the last two decades. Nearly 45 acres of forest were covered with monarchs in the winter of 1995-1996, and from that time, their populations fluctuated annually until 2003-2004, when scientists recorded 27.5 acres of forest coverage. Since then, surveys have documented a continued downward average trend.

Threats to monarch butterflies

Migratory monarch populations need large, healthy forests to protect them from winds, rain, and low temperatures common at night in the forests where they overwinter in Mexico and California. While logging of the monarch butterfly’s overwintering habitat in central Mexico has harmed the species in the past, the impacts of habitat destruction, insecticides, and herbicides within the species breeding grounds in the US and Canada, along with the effects of climate change, are the major drivers of its decline today.

Milkweed matters

Milkweed is the only plant on which monarchs will lay their eggs and the only source of food for baby caterpillars. But urban planning and agricultural expansion in the United States and Canada have paved and plowed over millions of acres of milkweed. The development of genetically modified (GMO) Roundup Ready crops has played a major role in the loss of milkweed in agricultural areas. These GMO crops don’t directly harm the butterfly. Rather, it is their ability to resist Glyphosate, a weed killer and the primary active ingredient in Roundup, that has eliminated 99% of the milkweed that once grew in corn and soybean fields.

The good news is that many of us can take action to help milkweed and the monarch. By planting milkweed or simply letting it grow, you support monarch breeding and migration.

Insecticides and monarchs

A second factor that has harmed monarch butterflies is neonicotinoids (neonics), a class of neurotoxic insecticide. Although marketed as a safer option for selectively killing pests, neonics have instead made US agriculture 48 times more toxic to most insects, including pollinators. These pesticides are affecting entire food chains as they are persistent in the environment, infiltrate groundwater (highly water soluble), and have cumulative and largely irreversible effects on invertebrate populations.

The Monarch Butterfly Biosphere Reserve in central Mexico.

How WWF is helping monarchs

WWF started working on monarch butterfly conservation in Mexico at the end of the 1990s by contributing with an analysis of the monarch colonies resulting in a Presidential Decree that extended the protected area in the year 2000 from 40,000 acres to 139,000 acres (about half the area of San Antonio, Texas), calling it the Monarch Butterfly Biosphere Reserve. The protected area includes a buffer zone of 105,533 acres and a core zone of 33,500 acres, where monarchs have historically established their colonies.

In 2003, WWF opened the Monarch Program and has since collaborated with local communities, scientists, and the Mexican government to promote sustainable forest management that benefits both nature and people. Beyond monarch education and ecotourism, we work with partners to provide financing and technical assistance on projects such as mushroom farming and tree nurseries. By the end of 2024, more than 21 million oyamel and pine trees have been produced in a network of 13 community-based nurseries; more than 53 acres of forest have been reforested inside the Monarch Butterfly Reserve and surrounding protected areas; and 34 permanent jobs and 130 temporary jobs have been created.

Also in Mexico, WWF leads two reports every year at the Monarch Butterfly Biosphere Reserve:

The survey of the area of forest that monarchs occupy during the winter, providing a scientific estimate of the size of the monarch population.
An analysis of forest degradation at the core zone of the Monarch Butterfly Biosphere Reserve.

In the US, WWF works to reduce neonicotinoid pesticides, which are absorbed into insect nerve cells and are a leading threat to monarch butterflies and other pollinators. We support a "middle-ground" approach that increases farmer access to non-neonicotinoid treated seeds. This agronomic justification method can benefit farmers' bottom lines and the environment. Farmers should have a say in how pests are managed on their lands while being provided with more information and options to move away from ubiquitous use of neonic-treated seeds that harm wildlife, soil organisms, aquatic systems, and humans. WWF also works with many leading food companies in the US to reduce the environmental impact from their crop production and increase biodiversity on their lands.

WWF's extensive network of partners, spanning government agencies, academic institutions, farm advisors, producer organizations, and grassroots organizations, allows for coordinated action and policy influence across different sectors. Additionally, WWF's global reach and reputation lend credibility to its initiatives, helping to raise awareness and drive change on both local and national levels.