Eastern monarch butterfly numbers in Mexico have nearly doubled since last winter.
The World Wildlife Fund's latest count of migratory monarch butterflies offers some encouraging news for the eastern population while the western population may be struggling to survive.
The organization's annual count released on Thursday does not measure individual butterflies but tracks the population by measuring the area that the insects cover in the forests of Central Mexico during their wintering period.
This year’s count of 4.42 acres of occupied forest habitat is nearly twice as large as last year's, but eastern monarch butterfly populations remain far below the long-term average. The 2024 figures fell 59% from 2023 to the second lowest level since record keeping began.
At the same time, the population of western monarch butterflies has seen a decline. The Xerces Society for Invertebrate Conservation monitors this population and reported the lowest count of monarch butterflies on record. Each year, the organization tracks the number of monarchs that migrate to the California coast, including Northern Baja, as well as areas in inland California and Arizona.
About the eastern monarch butterfly
Monarch butterfly migration patterns
The two monarch populations can migrate as far as 3,000 miles. The eastern monarchs travel north from Central Mexico toward the Central U.S. Some will even cross into Canada. The western monarchs fly about 300 miles from the Pacific Coast to inland areas in the West.
Protecting monarchs and forests
Monarch butterflies face several threats:
◾ Changes in climate in their breeding areas in Canada and the U.S. can affect the availability of milkweed, which is essential for laying eggs and feeding caterpillars.
◾ Changes in land use: Although illegal logging in their reserve in Mexico has stopped, if forest degradation at their overwintering sites continues, it could further stress the population.
◾ Use of herbicides and insecticides in the U.S. has led to a loss of milkweed and other plants that adult monarchs need for food.
Source: Paste BN Network reporting and research; WWF; UNESCO