The famous Monarch butterfly migration to a forest reserve in Mexico may disappear in the near future. Experts say the butterflies' numbers have dropped to their lowest ever, a decline that marks a long-term trend, CBS News reported.
Milkweed, the butterfly variety's food source, has been damaged by genetically modified crops.
According to Lincoln Brower, a leading entomologist at Sweet Briar College in Virginia, "the migration is definitely proving to be an endangered biological phenomenon."
GMOs have influenced the Monarch butterfly's diminishing numbers, along with such factors as urbanization, extreme weather and illegal logging.
"The main culprit," Bower wrote in an email, is genetically modified "herbicide-resistant corn and soybean crops and herbicides in the USA" that "leads to the wholesale killing of the monarch's principal food plant, common milkweed."
The butterflies are now only found in 1.65 acres in the pine and fir forests west of Mexico City, compared with 2.93 acres in 2013, according to a report from the World Wildlife Fund, Mexico's Environment Department and the Natural Protected Areas Commission.
At their peak, the black and orange butterflies covered more than 44.5 acres in 1996, according to CBS. Remembering the route through instinct, they fly thousands of miles annually to a forest reserve in central Mexico that covers 193,000 acres.
The journey from Canada and the United States to Mexico each winter is the biggest migration of Monarch butterflies in the world and the second-largest insect migration next to a dragonfly species in Africa.
Monarch butterflies exist in other parts of the world, so the species wouldn't go extinct any time soon, but those in the U.S. and Canada would have to find somewhere else to winter in order to survive.
Some gardeners and home owners have started planting milkweed to replace the butterflies' lost habitat, according to CBS.
Experts announced the species' diminished numbers right after the 20th anniversary of the North American Free Trade Agreement between the U.S., Canada and Mexico. The three nations signed environmental accords to protect migratory species and took the Monarch butterfly as their mascot of sorts.
"Twenty years after the signing of NAFTA, the Monarch migration, the symbol of the three countries' cooperation, is at serious risk of disappearing," said Omar Vidal, the World Wildlife Fund director in Mexico.
People who live near the famous forest reserve have already begun to miss the Monarch butterflies, which often appear as early as the Nov. 1-2 Day of the Dead holiday.
"They were part of the landscape of the Day of the Dead, when you could see them flitting around the graveyards," said Gloria Tavera, the director of the reserve. "This year was the first time in memory that they weren't there."
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