A first-ever comprehensive study of butterfly populations across the United States shows dramatic declines in most species.
Overall, about 22% have died off in just 20 years. And 114 species have declined by 40% or more.
“It's much more sobering than I could have imagined when we started this work,” said senior author Cheryl Schultz, a professor of conservation biology at Washington State University. “We're losing our butterflies.”
Schultz said she had been studying butterflies in the Northwest since the early 1990s, when it became apparent to her through contacts with researchers in more and more places that declines seemed to be happening everywhere.
“Just reports at so many levels that there are just fewer butterflies in the landscape. And there was a bunch of discussion in the academic literature about how big a problem this is. And there were some reports that were coming out about really dramatic declines, and others that were kind of questioning that,” she said.
She wanted to get to the bottom of it. So, about a decade ago, she put together the proposal for a comprehensive butterfly study and sought funding.
Collin Edwards, a postdoc researcher in Schultz’s lab at WSU, developed and ran the computer models that pulled all of the data together.
“The reason that it hadn't been done before was that we had so many different sources of data across the country,” Edwards said.
“And convincing everyone that it made sense to share their data with us, but then also just integrating all that data and figuring out how to model it in a way that made sense was a massive challenge.”
Edwards now works for the state Department of Fish and Wildlife, doing ecological modeling to count salmon.
The study was published March 6 in the journal Science. It was completed by nearly two dozen researchers in the Status of Butterflies in the U.S. working group, which formed to bring together all available butterfly monitoring datasets and develop a picture of the health of butterfly populations across the contiguous United States.
Among the findings: about a third of the species in their analysis have lost more than 50% of their populations in the past 20 years. And many have lost more than 90%.
Butterflies of the Pacific Northwest fared better overall, compared with other regions of the United States that are hotter and more prone to draught.
Schultz said the declines are less dramatic, but species in the Northwest are still declining overall and not increasing.
A triple threat is killing numerous species
Pesticides, climate change and habitat loss are all key causes of the declines. And these forces often combine to cause even more harm to butterflies. However, Schultz said we should not lose hope.
“Butterflies are amazingly resilient, and they are able to increase rapidly from small numbers,” she said.
A case in point for both Schultz and Edwards is the Fender’s blue butterfly, which Schultz worked with for her PhD at the University of Washington. It was believed to have gone extinct in 1936, but was rediscovered in 1989.
Endemic to the upland prairies of Oregon's Willamette Valley but threatened by habitat loss, it was listed as an endangered species in the year 2000. That enabled work to recover it.
And today, Schultz says it bounced back from just a few thousand in butterflies in the 1990s to as many as 30,000 today. In 2023, it was down- listed from endangered to threatened.
Exemplifying resilience
Edwards said despite the daunting triple threat that they face, butterflies are amazingly resilient - because they have very fast generation time and often lay thousands of eggs per year.
“If we give them good conditions, they really have the chance to recover rapidly. They populations can really explode when we make things better for them,” he said.
Schultz said that even in a place where more than 95% of the land is private, people did what it took to get the small blue fliers going again. Recalling that fuels her optimism.
Landowners purchased native flower seeds and planted them on their prairies, or worked on restoration projects such as controlled burns to eliminate invasive vegetation with the U.S. Fish and Wildlife Service Partners Program.
“People came together at the table and said, what's going on? What's the science we need to know to turn these around? And we're committed to using that science in the community and doing that work,” she said.
She said it’s not just the owners of larger properties that can help; people in cities and suburbs can take simple actions too, like planting small patches of flowers – or letting weeds like dandelions grow. These small actions can help many struggling butterfly species to rebuild.
Still, Edwards said the underlying science needs support that will likely be far less available in the coming years.
The working group that powered their study was hosted by the U.S. Fish and Wildlife Service’s Center for Pollinator Conservation, as well as the U.S. Geological Survey’s John Wesley Powell Center for Analysis and Synthesis. Its funding came almost entirely from those federal agencies, both of which may see cuts under the new Trump administration.
