Monarch Butterfly Population Increases by 64% in Mexico

The eastern migratory monarch butterfly population has shown a significant increase in its wintering grounds in central Mexico, according to data released by World Wildlife Fund (WWF)-Mexico and its partners. The area of forest occupied by the butterflies during the 2025-2026 winter season grew by 64% compared to the previous year.

The annual census, released on March 17, 2026, indicates that the butterflies covered 7.24 acres of habitat, an improvement from the 4.42 acres recorded the previous winter. In metric terms, the occupied surface reached 2.93 hectares, up from 1.79 hectares in the prior year, marking the highest population level since 2018.

The eastern monarch population, which migrates between Canada and Mexico, is considered at risk due to a drastic decline over recent decades. These butterflies travel approximately 4,800 kilometers each year to reach the forests of Mexico for hibernation.

Drivers of the Population Increase

Conservation efforts within the Monarch Butterfly Biosphere Reserve have played a critical role in this recovery. Stricter conservation policies and collaboration between international organizations, authorities, and local communities have led to a sharp decrease in illegal logging. WWF reports that affected areas dropped from hundreds of hectares to just 2.55 hectares between 2024 and 2025.

Environmental conditions also contributed to the increase. A joint report from WWF and the National Commission of Protected Natural Areas noted that more favorable weather conditions during the migration and hibernation periods enhanced the survival rates of the species.

Persistent Threats and Long-term Concerns

Despite the 64% jump, scientists warn that the population remains well below historic norms. In 1995, the butterflies occupied more than 18 hectares of forest, compared to the current area of less than 3 hectares. According to the U.S. Fish and Wildlife Service, a minimum of 6 hectares is necessary to ensure the long-term survival of the species.

While an increase is great news, the numbers in Mexico are still well below historic norms

Scott Black, director of the Xerces Society for Invertebrate Conservation

Major threats persist outside of the Mexican hibernation sites. In the United States, the intensive use of herbicides has reduced the availability of milkweed, the essential plant required for monarch reproduction. Without milkweed, caterpillars cannot develop, which severely limits population growth.

Additional pressures include climate change and the expansion of agricultural land, which continue to drive habitat loss. Experts emphasize that annual fluctuations often draw public attention, but the primary concern remains the long-term decline caused by pesticides and environmental degradation.

Regional Divergence in Butterfly Populations

The recovery of the eastern population stands in stark contrast to the status of the western monarch population. The Xerces Society’s Western Monarch Count, conducted in late November, recorded only 12,260 monarchs overwintering in coastal California tree groves.

This figure represents the third lowest number ever recorded for the western population, falling significantly short of the millions of butterflies observed in the 1980s, which scientists categorize as a stable population level.

The current increase in Mexico is viewed as a turning point that demonstrates the effectiveness of conservation measures, though the overall ecological balance remains fragile. The future of the species depends on maintaining these protective efforts across the entire migratory route spanning Mexico, the United States, and Canada.