US monarch butterfly population sees significant drop in last 2 decades: Study

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Karah Rucker Anchor

By Karah Rucker (Anchor), Shea Taylor (Producer), Jake Larsen (Video Editor)

The United States’ butterfly population dropped 22% over two decades, a steep decline for the vital pollinators. Researchers looked at more than 76,000 studies to create the most comprehensive population study ever.
When it comes to monarch butterflies, specifically, the U.S.’ eastern population went up this year.
Meanwhile, the U.S.’ western population saw its lowest numbers ever.

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Spring is nearly here and many people are looking forward to sunny days but one indicator of spring might not be seen as much. The butterfly population in the United States decreased 22% between 2000 and 2020, according to a new study.

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What did researchers find?

Researchers looked at more than 76,000 regional surveys to create the most comprehensive study of their population yet and came to that conclusion.

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However, there is some encouraging news for these vital pollinators, at least in the eastern U.S.

Good news for the eastern US population

According to the Wild Wildlife Fund’s annual report, the eastern monarch population nearly doubled in 2025. The eastern monarch population is located east of the Rocky Mountains and they travel to Mexico for the winter annually.

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The WWF tracks the population by how much space the insects cover in central Mexico’s forests. In 2025, they occupied 4.42 acres, up from 2.22 acres in 2024.

Bad news for the western US population

Meanwhile, the western monarch butterfly population declined.

The western monarch population is tracked by the Xerces Society for Invertebrate Conservation. It counts the number of monarch butterflies that migrate to the California coast in northern Baja and inland California, and Arizona each year.

In 2025, the Xerces Society recorded its lowest number of monarch butterflies ever.

Is this only an issue in the US?

The drop in butterfly numbers in the U.S. mirrors the overall estimated average rate of insect loss of about 1% to 2% per year that has been seen worldwide.

This “insectageddon” has negative implications for the world’s food supply because about one-third of all crops depend on pollinators like butterflies and bees to thrive.

How can you help?

There are several ways everyone can help save the butterflies and other important pollinators. Here are several resources from the Xerces Society anyone can use to help support pollinator populations:

Tags: Arizona, Bees, California, Conservation, food, Mexico, Population, Research, Study, United States, Wildlife

[Karah]

SPRING IS UPON US AND WHILE MANY ARE LOOKING FORWARD TO SUNNIER DAYS AND FLOWERS IN BLOOM – THERE’S ONE SPRING STAPLE YOU MIGHT NOT SEE AROUND AS OFTEN.

THE UNITED STATES’ MONARCH BUTTERFLY POPULATION IS SEEING AN ALARMING DECLINE… WITH A NEW STUDY SHOWING **OVERALL** NUMBERS WENT **DOWN** 22 PERCENT BETWEEN 2000 AND 20-20 – ACCORDING TO THE MOST COMPREHENSIVE STUDY OF THEIR POPULATION YET.

RESEARCHERS LOOKED AT MORE THAN 76-THOUSAND REGIONAL SURVEYS TO COME TO THAT CONCLUSION.

HOWEVER – THERE IS **SOME** ENCOURAGING NEWS FOR THESE VITAL POLLINATORS, AT LEAST IN THE EASTERN U-S.

ACCORDING TO THE WORLD WILDLIFE FUND’S ANNUAL REPORT – THE EASTERN MONARCH POPULATION, WHICH IS TO THE EAST OF THE ROCKY MOUNTAINS ACTUALLY **WENT UP**… NEARLY DOUBLING THIS YEAR.

THOSE BUTTERFLIES TRAVEL TO MEXICO FOR THE WINTER.

THE W-W-F TRACKS THE POPULATION BY HOW MUCH SPACE THE INSECTS COVER IN CENTRAL MEXICO’S FORESTS.

THIS YEAR THEY OCCUPIED NEARLY FOUR AND A HALF ACRES – WAY UP FROM 2 POINT 22 ACRES LAST YEAR.

MEANWHILE, THE WESTERN MONARCH BUTTERFLY POPULATION WENT DOWN.

THAT POPULATION IS TRACKED BY THE XERCES (zer-sees) SOCIETY FOR INVERTEBRATE CONSERVATION.

THEY COUNT THE NUMBER OF MONARCH BUTTERFLIES THAT MIGRATE TO THE CALIFORNIA COAST — NORTHERN BAJA AND INLAND CALIFORNIA — AND ARIZONA EACH YEAR.

AND THIS YEAR – THEY RECORDED THEIR LOWEST NUMBER **EVER**.

THE DROP IN BUTTERFLY NUMBERS IN THE U-S MIRRORS THE OVERALL ESTIMATED AVERAGE RATE OF INSECT LOSS OF ABOUT 1 TO 2 PERCENT PER YEAR THAT HAS BEEN SEEN AROUND THE WORLD.

THIS SO-CALLED “INSECTAGEDDON” HAS DIRE IMPLICATIONS FOR THE WORLD’S FOOD SUPPLY FOOD SUPPLY BECAUSE ABOUT ONE-THIRD OF **ALL** CROPS DEPEND UPON POLLINATORS BUTTERFLIES AND BEES TO THRIVE.

THERE ARE WAYS YOU CAN HELP SAVE THE BUTTERFLIES – AND BY EXTENSION, OUR WORLD.

YOU CAN FIND THOSE DETAILS RIGHT NOW ON THE STRAIGHT ARROW NEWS APP.