Butterfly populations in the U.S. declined by 22% from 2000 to 2020, with 13 times as many species declining as increasing.
Butterflies are disappearing in the United States. All kinds of them. With a speed scientists call alarming, and they are sounding an alarm.
A sweeping new study published in Science tallies butterfly data from more than 76,000 surveys across the continental United States for the first time. The results: between 2000 and 2020, total butterfly abundance declined by 22% across the 554 species counted. In other words, for every five butterflies in the contiguous U.S. in the year 2000, only four remained in 2020.
“Action must be taken,” said Elise Zipkin, a Red Cedar Distinguished Professor of quantitative ecology at Michigan State University and a co-author of the paper. “To lose 22 percent of butterflies across the continental U.S. in just two decades is distressing and shows a clear need for broad-scale conservation interventions.”
Zipkin and her MSU colleague and co-author Nick Haddad, professor of integrative biology, have been major figures in drilling down the state of U.S. butterflies. Zipkin has been a formidable numbers cruncher with successes gleaning hard facts from imperfect data sets to better understand the natural world.
Haddad is a terrestrial ecologist, a scientist on the ground specializing in the fates of the most fragile and rare butterfly populations. The widespread decline of butterflies found in this study has shaken Haddad, and reports that the mountain of data is on display in his Michigan neighborhood.
“My neighbors notice it,” Haddad said. “Unprompted, they’ll say, ‘I’m seeing fewer butterflies in my garden, is that real?’ My neighbors are right. And it’s so shocking.”
The Scope and Methods of the Study
In this paper, Zipkin and Haddad were among a working group of scientists with the USGS Powell Center for Analysis and Synthesis that aggregated decades of butterfly data from 35 monitor programs that included records of over 12.6 million butterflies. Using data integration approaches, the team examined how butterfly abundances changed regionally and individually for the 342 species with enough data.
Abundance is a term that threatens to become ironic. Butterfly populations dropped an average of 1.3% annually across the country, except for the Pacific Northwest. But even that encouraging result came with a caveat. Further scrutiny of the apparent 10% increase in overall abundance in the Pacific Northwest over the 20-year study period was credited largely to the California tortoiseshell butterfly, which was enjoying a population boom not expected to be sustained.
Butterflies are the most surveyed insect groups, courtesy of extensive volunteer-based and expert science monitoring programs. Until now, studies have focused on individual species – most notably monarch butterflies – or limited to specific locations.
This new study uses all the available regional butterfly monitoring data within the continental United States and then develops a method of analysis that appropriately accounts for variations in collection protocols across programs and regions to produce comparable results for hundreds of species.
“This is the definitive study of butterflies in the U.S.,” said Collin Edwards, the study’s lead author. “For those who were not already aware of insect declines, this should be a wake-up call. We urgently need both local- and national-scale conservation efforts to support butterflies and other insects. We have never had as clear and compelling a picture of butterfly declines as we do now.”
Edwards had been a postdoctoral research associate at Washington State University, Vancouver, and now works at the Washington Department of Fish and Wildlife.
The Impact on Ecosystems
The results reveal that 13 times as many species declined as increased – with 107 species losing more than half their populations.
Zipkin and Haddad say butterflies are more than fluttering symbols of freedom and beauty. They play important roles in cycling nutrients and are a significant food source for other organisms such as birds. Over the last 50 years, North America has lost nearly 3 billion birds, a decline at almost identical rates of the butterflies.
Butterflies are important and forgotten pollinators. People often think of bees first, but butterflies (and flies) are responsible for $120 million of cotton production in Texas, for example.
Zipkin said she sees this paper as an important heads-up to the country’s policymakers. “People depend on plants, microbes, and animals for the air we breathe, the water we drink, and the food we eat. Yet, we are losing species at rates that rival the major mass extinction events on our planet,” Zipkin said. “The U.S. plays an important role in setting policies and creating laws that conserve and protect biodiversity from local to global scales. Our leaders and the federal government, in particular, are responsible for making sure future generations have the necessary resources to thrive.”
In 2024, Haddad was part of a study published by the journal PLOS ONE that pinpointed the danger of insecticides, which rose above other threats such as habitat loss and climate change in reducing butterfly abundance and diversity. He points out that saving butterflies isn’t a hopeless problem, just one that requires will.
A lot of insecticide use, he said, lacks strategy and results in overuse. Some 20 percent of cropland suffers from poor yields. Creating policies that return under-producing land to nature could help the butterflies to rally.
“Prophylactic and near-universal application of insecticides harms butterflies and other beneficial insects, with no proven benefit to crop yield,” Haddad said. “What is applied as ‘insurance’ is extracting a great debt to agroecosystems. The good news is that the widespread application of insecticides can be reversed, and butterflies and other pollinators will recover.”
Reference: “Rapid butterfly declines across the United States during the 21st century” by Collin B. Edwards, Elise F. Zipkin, Erica H. Henry, Nick M. Haddad, Matthew L. Forister, Kevin J. Burls, Steven P. Campbell, Elizabeth E. Crone, Jay Diffendorfer, Margaret R. Douglas, Ryan G. Drum, Candace E. Fallon, Jeffrey Glassberg, Eliza M. Grames, Rich Hatfield, Shiran Hershcovich, Scott Hoffman Black, Elise A. Larsen, Wendy Leuenberger, Mary J. Linders, Travis Longcore, Daniel A. Marschalek, James Michielini, Naresh Neupane, Leslie Ries, Arthur M. Shapiro, Ann B. Swengel, Scott R. Swengel, Douglas J. Taron, Braeden Van Deynze, Jerome Wiedmann, Wayne E. Thogmartin and Cheryl B. Schultz, 6 March 2025, Science.
DOI: 10.1126/science.adp4671
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3 Comments
An important question that wasn’t even asked, let alone answered, is why are some populations relatively unaffected? If global warming, which affects the entire globe, were responsible, one would naively expect all populations to be experiencing similar declines. Although, 0.5 deg’s C warming over the last 50 years, with the predominate warming at night and in the Winter (when butterflies are not active) would seem to be an unreasonable sensitivity when adults and larvae in the summertime experience changes 5X that daily.
Land-use changes undoubted play a role because pavement and roofs do not grow food for caterpillars! Also, monoculture agricultural fields that experience tilling, weeding, and chemical applications are not hospitable to anything except the specific insect adapted to the cultivar.
On the other hand, if pesticide spraying (a documented problem) is responsible, then one would reasonably expect the declines to be concentrated in agricultural areas that host the impacted areas. Is that the case? The article doesn’t provide an answer.
New Science magazine article pointed out that pesticides, fertilizers. and herbicides are taken up into clouds that rain these products on the planet.
My midwestern yard has only one species of butterfly even though I Have many plants for host and nevtar and never use pesticide or herbicides.
There have been major political changes in North America in the last 50 years that have had caused a major shift in psychological thought, one of which poses a treat to butterflies; “butterflies are more than fluttering symbols of freedom and beauty.” The idea of freedom and beauty, has now become problematic, for many, and has resulted in most AG agencies, warning producers to destroy milkweeds and other such plants that are vital to the survival of butterflies.