Monarch butterflies gather on a tree in central Mexico.

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The Flight of Their Lives

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

September 2, 2024
By Mary Kay Carson and Nicole Tocco

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

Each fall, an amazing scene plays out in the forests of central Mexico. Millions of monarch butterflies cover the trees in a sea of black and orange. The monarchs have flown hundreds of miles to reach their winter home. It is one of the planet’s most epic migrations.

But scientists estimate that, last winter, the number of monarchs in Mexico dropped nearly 60 percent from the year before. The drop is part of a trend that’s seen the overall number of monarchs dip over the past 30 years. Experts are concerned that monarchs may one day disappear.

“For almost any population of living organisms, there is a point of no return,” says entomologist Karen Oberhauser. 

Can we help save monarchs before it’s too late?

A Long Journey

Monarchs are the only insects that migrate south for the winter. The butterflies spend the spring and summer in the northern U.S. and southern Canada. They can’t fly in the cold, so they begin to take off for warmer weather in late summer. Some butterflies that head to Mexico travel about 3,000 miles to get there.   

It will be the butterflies’ first and only trip to Mexico. After spending months huddled together on trees, 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. 

Then the new generation will make the journey to Mexico next fall. Even though they’ve never been there, they’ll land on the same trees their ancestors did. How? That’s a mystery scientists are still figuring out.

Butterfly Bots

Scientists use tiny sensors to map the monarchs’ journey. The sensors weigh less than a few grains of rice and are attached to the bodies of some migrating monarchs. Data from the sensors helps researchers pinpoint areas along migration routes that need protection.

Will & Deni McIntyre/Science Source

Troubled Times

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

One reason is the loss of habitat along their migration routes. To make way for homes and farmland, people have cut down many of the trees where monarchs live.

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. Rising temperatures and droughts have 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, monarch habitats would be protected by the government.

For now, wildlife groups are replanting trees and working to prevent habitats from being destroyed. 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.”

Monarch Migration

Between August and October, most monarchs in North America fly to Mexico. But some smaller groups go to Florida or the California coast.

Jim McMahon/Mapman®

1. What trend does the author discuss in the first section of the article?

2. What does the article say is a mystery that scientists are still figuring out?

3. Describe two threats that monarch butterflies face.

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