Butterflies are disappearing from the United States at an alarming rate, with their total population declining by more than a fifth over two decades, a new study has found.
Total butterfly abundance — the total individuals of a species within a given area — plummeted by 22 percent between 2000 and 2020, according to the study, published Thursday in Science.
During that period, about 33 percent of butterfly species underwent significant shrinkage, while many experienced extreme declines in abundance, the research showed.
“For those who were not already aware of insect declines, this should be a wake-up call,” said lead author Collin Edwards, of the Washington Department of Fish and Wildlife, in a statement.
To draw their conclusions, Edwards and his colleagues from around the country combed through data from 76,000 surveys — a lofty task, as most butterfly monitoring efforts are either volunteer-based or conducted by experts on a limited geographic or species level.
The researchers worked with colleagues at the U.S. Geological Survey's Powell Center for Analysis and Synthesis, who aggregated the data from 35 monitoring programs and with records of more than 12.6 million individual butterflies.
Of the 554 species included, the scientists said they had sufficient data to examine how butterfly abundances changed regionally and individually for 342 species. Ultimately, their results revealed that 13 times more species declined than increased, with 107 species losing at least half of their populations.
Butterfly populations plunged an average of 1.3 percent annually nationwide over the past two decades — leaving little room for optimism in most parts of the country.
Even in areas that experienced butterfly growth, the authors expressed little hope — particularly in the Pacific Northwest, which boasted a 10 percent abundance surge, according to the data. The authors cautioned against celebrating, as they largely credited that spike to the California tortoiseshell butterfly and did not expect that population boom to persist.
Although butterflies are primarily known for their beauty, the scientists emphasized the critical roles they play as pollinators and in cycling nutrients, as significant food sources for other organisms. For example, butterflies provide meals to birds, which have declined at an almost identical rate as their fluttering prey over the past 50 years, the authors noted.
“People depend on plants, microbes, and animals for the air we breathe, the water we drink, and the food we eat," co-author Elise Zipkin, a professor of quantitative ecology at Michigan State University, said in a statement. "Yet, we are losing species at rates that rival the major mass extinction events on our planet.”
Co-author Nick Haddad, a Michigan State professor of integrative biology, also cited the dangers linked to overuse of insecticides, which he said has harmed butterflies without improving crop yields. He stressed, however, that abandoning this practice — and thereby saving the insects — is possible and practical.
"The widespread application of insecticides can be reversed, and butterflies and other pollinators will recover," Haddad said in a statement.
Eliza Grames, another co-author and a biologist at Binghamton University, echoed these sentiments, adding that the scientists now have better data to support considering butterflies for federal protection.
"We can go in, conserve their habitat and – hopefully – they can rebound,” Grames said.
Edwards, meanwhile, emphasized the need to strengthen conservation efforts that bolster butterfly populations on both a local and national scale.
"We have never had as clear and compelling a picture of butterfly declines as we do now," he added.