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 for the first time tallies butterfly data from more than 76,000 surveys across the continental United States. The results: between 2000 and 2020, total butterfly abundance fell by 22% across the 554 species counted. That means that for every five individual butterflies within the contiguous U.S. in the year 2000, there were only four 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 have 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."
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 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, that 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."
In addition to Zipkin, Haddad, and Edwards, "Rapid butterfly declines across the United States during the 21st century" was written by Erica Henry, Matthew Forister, Kevin Burls, Steven Campbell, Elizabeth Crone, Jay Diffendorfer, Margaret Douglas, Ryan Drum, Candace Fallon, Jeffrey Glassberg, Eliza Grames, Rich Hatfield, Shiran Hershcovich, Scott Hoffman-Black, Elise Larsen, Wendy Leuenberger, Mary Linders, Travis Longcore, Daniel Marschalek, James Michielini, Naresh Neupane, Leslie Ries, Arthur Shapiro, Ann Swenger, Scott Swengel, Douglas Taron, Braeden Van Deynze, Jerome Wiedmann, Wayne Thogmartin, and Cheryl Schultz.
Zipkin and Haddad are members of MSU's Ecology, Evolution, and Behavior Program , of which Zipkin is director.
