Monarch butterflies gather on a tree in central Mexico.

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Monarchs on the Move

Monarch butterflies take a long journey each year. But will they be able to make the trip for much longer? 

September 16, 2024
By Mary Kay Carson and Nicole Tocco

As You Read, Think About: Why has the number of monarch butterflies dropped?

One of the largest migrations on Earth is taking place right now—and it might be happening in your backyard. In mid-August, millions of monarch butterflies started flying south from the U.S. and Canada. Some will travel as far as 3,000 miles to reach forests in central Mexico. For several months, the fir trees in the butterflies’ winter home will be blanketed in orange and black.

Scientists are anxious to find out how many monarchs make the trip this year. Last winter, the number of monarchs in Mexico dropped nearly 60 percent from the year before. It’s part of a trend that has seen the monarch population fall sharply over the past 30 years. Experts are concerned about the future of the butterflies.

“For almost any population of living organisms, there is a point of no return,” says Karen Oberhauser. She’s an entomologist who has studied monarch butterflies for more than 30 years. 

Can we help save these colorful butterflies before it’s too late?

An Epic Journey

To escape cold winter temperatures, most monarchs in North America fly south to Mexico (see “Monarch Migration,” below). The butterflies headed there now are only a few weeks old. 

They’ll spend months clustered on fir trees in Mexico for warmth. Then this group of monarchs will begin to migrate north next spring. But they won’t make it all the way back. Their offspring and the generations that follow will complete the trip. 

The butterflies that migrate to Mexico next year will be the great-great-grandchildren of those that are flying there now. Though the migrating monarchs have never traveled that route, they will find their way to the same forests that past generations did. Exactly how the butterflies know where to go is a mystery to scientists. 

“We don’t understand how they have a map in their head,” Oberhauser explains.

Monarch Migration

From August to October, most monarchs in North America fly to Mexico. But some travel to Florida or the California coast. Future generations complete the trip back north.

Jim McMahon/Mapman®

Source: The Xerces Society

Troubled Times

But this amazing migration may not happen for much longer. Scientists estimate that more than 360 million monarchs spent the winter in Mexico in 1996. Last year, that number was about 18 million.

One reason for the decline is habitat loss. To make way for homes and farmland, people have cut down many of the trees where monarchs spend their winters.

But the biggest threat is the disappearance of a plant called milkweed. It’s the only plant on which monarchs lay eggs. And monarch caterpillars eat only milkweed leaves. 

Some farmers and homeowners spray herbicides to kill weeds. The chemicals have wiped out millions of acres of milkweed. Hotter, drier weather brought on by climate change has also hurt the plant.

Hope for the Future

The U.S. Fish and Wildlife Service is considering adding monarchs to the endangered species list. If that happens, the butterflies’ habitats would be protected by the government.

For now, wildlife groups are replanting trees and working to prevent monarch habitats from being damaged further. They also encourage people who live along migration paths to plant milkweed.

“Everybody can help,” says Oberhauser. “A monarch habitat can be as small as someone’s tiny garden in their backyard.”

Trip Tracker

What routes do migrating monarchs take? Where do they stop along the way? To help protect monarch habitats, an organization called Monarch Watch tries to answer those questions and more. And it gets help from volunteers across the country.

The volunteers catch monarchs and carefully attach tiny stickers, called tags, to their wings. (The tags don’t harm the butterflies.) Volunteers use an app to share the tagging data about the monarchs they spot. That helps scientists at Monarch Watch track the butterflies’ movements. 

Will & Deni McIntyre/Science Source

1. What trend does the author discuss in the second paragraph of the article?

2. What part of monarch migration does the article say is still a mystery to scientists?

3. Describe two threats that monarch butterflies face.

Elnur/Shutterstock.com
entomologist

noun

a scientist who studies insects

 

The entomologist examined the pattern on the wings of the butterfly he had found.
PHOTOCREO Michal Bednarek/Shutterstock.com
climate change

noun

a gradual change in Earth’s average temperature and weather patterns

 

Because of climate change, Earth is warming and polar sea ice is melting.
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