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.