'Catastrophic and Saddening': Research Shows US Butterfly Population Dropped 22% in Two Decades

A landmark study released Thursday in the journal Science found that the number of butterflies in the United States declined dramatically between 2000 and 2020.

"The prevalence of declines throughout all regions in the United States highlights an urgent need to protect butterflies from further losses," according to the abstract of the study, which was authored by over 30 researchers from around the country.

Between 2000 and 2020, total butterfly abundance in the contiguous United States fell by 22% across 554 recorded species. The study also reported widespread species-level decline, in addition to overall abundance decline. According to researchers, 13 times as many butterfly species are declining as they are increasing.

"It's pretty shocking, really, that we've lost that much biodiversity in such a short time," said Eliza Grames, a conservation biologist at Binghamton University in New York and one of the study authors, who spoke with WBUR about the findings.

The survey used data from multiple sources, including North American Butterfly Association, which is the "longest-running volunteer-based systematic count of butterflies in the world," as well as data from Massachusetts Butterfly Club, which "carries out organized field trips and records individuals' reports across the state in which participants identify and record butterflies seen."

Scientists and dedicated amateur enthusiasts helped collect the data, according to The Washington Post, which spoke with some of the researchers.

"Scientists could not get all the data we used," Nick Haddad, an ecologist and conservation biologist at Michigan State University who worked on the study, per the Post. "It took this incredible grassroots effort of people interested in nature."

The study identified pesticide use, climate change, and habitat loss as drivers of the decline.

The research echoes other scientific findings that have recorded widespread loss of insect abundance more generally, a phenomenon that's sometimes called the "insect apocalypse." Bugs do many important things, like pollinating crops and keeping soil healthy. "As insects become more scarce, our world will slowly grind to a halt, for it cannot function without them," wrote biologist Dave Goulson in 2021.

Entomologist David Wagner, who was not involved in the study, told the Post in an email that butterflies function as a "yardstick for measuring what is happening" among insects generally. He said the findings of the study were "catastrophic and saddening."