U.S. Butterflies Are Disappearing at Drastic Rates, With One in Five Gone Since 2000

Butterfly populations in the United States have dropped by almost a quarter in the last two decades, according to a new analysis published last week in the journal Science.

A team of more than 30 researchers analyzed 12.6 million butterfly sightings across 76,000 population surveys. They found that between 2000 and 2020, the country lost 22 percent of its butterflies.

“It’s such a short timespan to lose this many butterflies, it’s very sobering,” says Eliza Grames, a biologist at Binghamton University and a study co-author, to Oliver Milman at the Guardian. “This is a wake-up call—people should be really concerned about this rate of loss and what we stand to lose. People like butterflies, but it’s going to take a lot of work to turn things around.”

The surveys used by the researchers included data collected both from scientists and community volunteers. Together, they conducted the most comprehensive assessment of butterflies in the country to date. “Scientists could not get all the data we used,” explains study co-author Nick Haddad, an ecologist at Michigan State University, to Dino Grandoni at the Washington Post. “It took this incredible grassroots effort of people interested in nature.”

Overall, the researchers were able to draw specific conclusions for 342 of the 554 species observed. They found that 33 percent of species had statistically significant declines. Only nine species—about 3 percent of the total—saw their numbers increase over the study period. More than 100 species declined by over 50 percent, and 22 species dropped by at least 90 percent.

“The median species declined by more than 40 percent,” says Collin Edwards, a quantitative ecologist at the Washington Department of Fish and Wildlife and the study’s lead author, to Jonathan Lambert at NPR. “That was where it really hit me that this is really big.”

Some of the most affected species include the Mitchell’s satyr, the painted crescent and the Florida white. Even traditionally widespread species have suffered, including the invasive cabbage white, which has seen its numbers drop by half. “That shocked me,” says Haddad to the New York Times’ Catrin Einhorn. “If even the cabbage white is declining, then, oh my God.”

While the study didn’t examine the reasons for these declines, the researchers suggest climate change, loss of habitat and insecticide use are the probable culprits. The Southwest saw the biggest regional drop in butterfly populations, likely because of drought conditions. The insects don’t hold much moisture, so they can dry out easily.

“The study is a much-needed, Herculean assessment,” writes David Wagner, an entomologist at the University of Connecticut who was not involved in the study, in an email to the Washington Post. “The tree of life is being denuded at unprecedented rates. I find it deeply disheartening. We can and must do better.”

Trends in butterfly numbers can act as an indicator for the health of insect populations more broadly, writes Grames in an article for the Conversation. And worldwide, insects have been dying off: More than 40 percent of insect species are in decline, according to a 2019 study. Their decrease nearly matches the annual drop of 1.3 percent that the study found for U.S. butterflies.

Actions to help your neighborhood butterflies could have wide-reaching effects, per the Conversation. Grames suggests growing native plants in your backyard and supporting conservation policies. “Even at a really local scale, improving habitats for butterflies or other insects can have a really dramatic impact,” says Edwards to Erik Stokstad at Science.

“Butterflies can recover quickly, because they have short generation times,” explains Grames to Maddie Molloy at the BBC. “Small actions like planting wildflowers, reducing pesticide use or even leaving part of a backyard unmowed can significantly improve their chances.”

“Insects are fundamental to life on Earth, and we need conservation actions and policies that support insects,” she adds.

Sara Hashemi | READ MORE

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.