Monarch butterfly population numbers down a second year in a row

The number of monarch butterflies spending the winter in Mexico has drastically declined in recent years, and experts are now reporting that their numbers are down for the second straight year in a row.

Monarch butterflies spend the winter season in Mexico and then migrate north into the United States and Canada in the spring and summer. Their populations are counted by the number of acres of trees that they occupy.

This year’s count of 6.12 acres is down from the 7.19 acres last winter. According to Monarch Watch, the butterflies were spread across 44 acres of trees just two decades ago. Since that time, there has been an 80 percent decline in their population.

Jorge Rickards is the head of the World Wildlife Fund in Mexico.

“The decrease is attributed to the presence of two tropical storms and three hurricanes that hit the Atlantic coasts in mid-September 2017 when migration begins,” said Rickards. “This impacted the number of Monarchs that arrived in Mexico.”

Rickards explained that unseasonably warm temperatures in the midwestern and northeastern United States also contributed to a late migration and lower numbers. He said that illegal logging and habitat destruction are the primary threats to the future of the Monarch butterfly.

“But how many monarch butterflies arrive to hibernate to the mountains of Mexico depend on how many can survive during their migration route in the United States, Canada and Mexico,” said Rickards.

In the United States, the use of herbicides has led to the widespread eradication of milkweed that monarch caterpillars feed on, and their survival is threatened as well. The U.S. Fish and Wildlife Service may soon declare the Monarch to be endangered, which would lead to measures to protect the species.

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By Chrissy Sexton, Earth.com Staff Writer