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Butterflies are rapidly fluttering out of existence from coast to coast, according to a new assessment published Thursday, at a rate that scientists worry could upend ecosystems and undercut pollination that sustains America’s crops.
The total number of butterflies in the contiguous United States has declined 22 percent over a 20-year period, according to a study in the journal Science, as shrinking habitat, rising temperatures and a toxic array of pesticides kill off the delicate insects.
The study, published Thursday in the journal Science, is the most comprehensive tally of U.S. butterfly populations to date.
Nick Haddad, a Michigan State University ecologist who co-wrote the study, said he once had a hard time believing his neighbors when they told him they see fewer butterflies than in the past.
“In my mind, I was nodding, thinking, ‘Oh, they just went out on a bad day,’” he said. But now, the data has him convinced.
“Butterflies are vanishing from the face of the earth,” he added.
The crisis for butterflies is part of a troubling downturn in the number of bumblebees, fireflies and other insects that has been observed in Europe, the Caribbean and other places worldwide. It could signal a potential “bugpocalypse” that scientists are fiercely debating — a shift that may spell trouble for both nature and society.
The loss of insects — “the little things that run the world,” as naturalist E.O. Wilson once put it — has dire implications for ecosystems in which birds and mammals rely on them for food and plants depend on them for pollination. Farmers and gardeners, meanwhile, may be losing allies that act as pollinators and natural pest control.
David Wagner, a University of Connecticut entomologist not involved in the study, said butterflies act as a “yardstick for measuring what is happening” among insects broadly. He called the new findings “catastrophic and saddening.”
“The study is a much-needed, Herculean assessment,” he wrote in an email. “The tree of life is being denuded at unprecedented rates. I find it deeply disheartening. We can and must do better.”
Researchers looked at over 12 million butterfly observations taken in 35 different monitoring programs across the contiguous United States from 2000 to 2020 for the study.
Some of those observations involved walking a predetermined path and noting every butterfly seen. Other counts were as informal as jotting down butterflies observed during a park visit. Both professional scientists and dedicated amateur enthusiasts collected crucial data.
“Scientists could not get all the data we used,” Haddad said. “It took this incredible grassroots effort of people interested in nature.”
Yet other butterfly counts, such as one run by biologist Jeffrey Glassberg in Westchester County, New York, involved teams of people canvassing landscapes 15 miles in diameter for every fluttering insect they could see.
Glassberg, who has been surveying the area for more than four decades, has witnessed about 10 species vanish. Among the lost is the ghostly white butterfly called Acadian hairstreak, which he suspects has retreated north as the climate warms.
“It kills me,” said Glassberg, who founded the North American Butterfly Association. But the butterfly counts his organization runs, he added, are important for building the next generation of butterfly lovers.
“You can’t save them if people don’t care about them,” he said.
Between 2000 and 2020, the total population of butterflies shrank by over a fifth, according to the study. A third of butterfly species showed significant declines while only 3 percent — nine species — experienced gains.
Among the kaleidoscope of species in steepest decline in the United States are the Florida white butterfly found in the Everglades and Keys, the Hermes copper butterfly native to Southern California and the tailed orange butterfly fluttering near the U.S.-Mexico border. Over 100 species have declined by more than 50 percent.
The findings likely underestimate the true scale of loss, said Wagner, since the researchers did not have enough data to make assessments of some of the rarest species also likely in decline.
But Matthew Moran, a biology professor at Hendrix College who has been skeptical of an insect apocalypse, cautioned the study only looks at two decades of data and may not show a full picture of long-term trends.
“However, it is clear that over the last 20 years, this group of well-studied and popular insects has undergone large declines, which should be concerning,” he added.
Three major factors weigh on butterfly populations, according to the researchers.
Roads, homes and other development are cutting up and stamping out meadows where butterflies once flew. And rising temperatures due to human-caused climate change are drying out vegetation in the habitats that remain.
“Every butterfly you see was a caterpillar that ate a plant,” said Collin Edwards, a quantitative ecologist who led the study. “So conditions that are bad for plants are going to be bad for butterflies.”
Many butterfly species tend to be doing better in the northern portions of their ranges, the researchers found, suggesting they are fluttering to higher latitudes to keep cool. The drought-stricken Southwest saw the steepest declines.
But the third and likely most important driver behind the butterfly bust is the boom in pesticide use since the 1990s, according to Haddad. In a previous study, he found the shift toward insecticides called neonicotinoids was the major cause for butterfly decline in the Midwest.
“That’s what I think is most worrisome,” he said.
At least one butterfly he has personally studied — the Saint Francis’s satyr, found only in North Carolina — may have already gone extinct. Its decline is documented in the study, which looked at data up to 2020, “but it actually could be gone by now.”
More than 30 butterflies are protected under the Endangered Species Act. The latest butterfly proposed for the list is the iconic monarch.
Unlike bears and birds and many other threatened animals, insects breed quickly. If given a chance — meaning if people restore meadows and minimize pesticide use — they can rebound in a few generations.
The researchers hope their findings act as an alarm bell for a public that loves to paint murals of butterflies and release them at weddings, but, they said, still does too little to protect them in nature.
“They’re beautiful, right?” Haddad said. “I do think there’s a way that butterflies enrich our lives through thinking about biodiversity that isn’t possible for all other insects.”