Hundreds of butterfly species across the American West are vanishing as the region becomes hotter, drier and more vulnerable to the effects of climate change, according to a study released Thursday.
The loss of butterflies across Western forests and prairies, like the similar drop in bumblebees nationwide due to rising temperatures, is troubling because both insects play a key role in pollinating crops and wildflowers. And the findings may add to fears among researchers of a broader die-off of insects that could be underway everywhere from Germany to Puerto Rico and beyond — a potential and debated bugpocalypse that threatens to upend ecosystems across the world.
In the United States, the alarming butterfly decline is most evident in Western areas where balmy summer temperatures creep well into the fall, drying out vegetation and potentially disturbing the seasonal cycles of the fluttering insects as they prepare for cooler months.
“The influence of climate change is driving those declines, which makes sense because they’re so widespread,” said Matt Forister, a biology professor at the University of Nevada at Reno and co-author of the study published in the journal Science. “It has to be something geographically pervasive.”
Scientists have long known that roadways, farms and other human development are stamping out meadows and other habitat for butterflies, while pesticides have further culled their numbers. Conservationists have taken to cordoning off areas as butterfly sanctuaries, planting vegetation such as milkweed for monarch butterflies as they migrate from Mexico across the Lower 48.
But the fact that widespread warming is weighing on such large numbers of butterflies across a vast geographic area suggests a more dire situation that cannot be abated simply by setting aside habitat. While the populations of butterfly species can vary widely from year to year, the researchers found an annual 1.6 percent drop in butterfly numbers in the Western United States over the last four decades.
Put another way: A butterfly spotter going to the same site every year saw about 25 percent fewer butterflies on average than 20 years ago.
David Wagner, an ecologist at the University of Connecticut who was not involved with the latest research, said the new findings are startling because “this is one of the first global cases of declines occurring in wildlands, away from densely populated human-dominated landscapes, and the rate of 1.6 percent is calamitous.”
The best-known butterfly on the decline in the drought-plagued region is the once-ubiquitous monarch, which used to arrive in California in such abundance every spring they regularly formed “a golden carpet” on the ground and filled the skies with “orangy” clouds, as John Steinbeck once wrote.
Now those orange itinerants are showing up in far fewer numbers. Since 1990, about 970 million monarchs have disappeared, according to a 2015 U.S. Fish and Wildlife Service report.
Other species, such as the common cabbage white butterfly and the imperiled, multicolored Edith’s checkerspot, are on downward trends, too, according to the analysis from Forister and his team.
“Rare species, common species, widespread species, local species,” said Forister, each had “detectable declines.”
The formal scientific findings jibe with what many motorists driving across the West have noticed recently: fewer bugs splattered across the front of their cars than during past road trips. Entomologists even have a name for it: the “windshield phenomenon.”
Forister said he has seen it “personally because I’ve been driving back and forth over the mountains for 20 years” from Reno and elsewhere on Interstate 80 to visit his parents in California’s Central Valley.
“It used to be that as soon as I showed up, my dad would get the hose out and obsessively clean the window,” Forister said. “He just doesn’t even do that anymore.”
The latest research is built on not only data collected by scientists across central California but observations across 10 other Western states scribbled into notebooks by butterfly enthusiasts out in the field or simply uploaded from smartphones by amateurs who make a hobby out of spotting rare species in their backyards.
“Even if you just took the professors that were on this paper, all of us, we couldn’t cover that geographic area,” said Katy Prudic, an entomologist at the University of Arizona who helps run one of the online butterfly databases. “There’s just not enough of us. So this work, the comparison across the entire West, could not be done without citizen science.”
Among the data used in the study are field notes from Marilyn Lutz and her husband, Joe Zarki, who have volunteered to run a butterfly count in Joshua Tree National Park for 25 years. The couple has been cataloguing birds and butterflies together ever since meeting in Yellowstone National Park in 1985.
They used to think they had trouble finding certain butterflies at higher elevations due to lack of experience. “But over time, we’re wondering if some of these are species that may be climate-change influenced,” said Zarki, who used to run educational programs at the park and is now retired.
Not every type of butterfly is in decline. Some are finding an edge in environments dominated by humans. The bright-orange Gulf fritillary, for example, is thriving not on native plants but on flowers popular in home gardens, Forister said.
And climate change itself may be a boon to butterflies in some places outside of the arid West. Using some of the same data as Forister and his team, Matthew Moran, a biology professor at Hendrix College in Arkansas, is working on a paper that he says will show an uptick in butterflies in the southeastern United States, where climate change is leading to more precipitation and plant growth.
“They got a really strong climate signal,” Moran said of the study published Thursday. The Western United States, he said, is “one of the more rapidly changing places in the continent. … If you look at it more continentwide, you will see more balancing-out.”
Still, efforts by federal wildlife officials to protect those butterflies in danger of vanishing entirely have had limited success. Of the 31 butterflies protected under the Endangered Species Act, only three are increasing in number, according to Noah Greenwald, endangered species director at the Center for Biological Diversity, a nonprofit environmental advocacy group.
Conservationists have struggled to get other imperiled butterflies added to the endangered list. In December, the Trump administration declined to declare the monarch endangered, citing limited resources, even as wildlife officials admit the decline is severe enough to warrant federal protection.
And the Center for Biological Diversity has fought for years to get the Sacramento Mountains checkerspot butterfly, a native of New Mexico’s high-elevation meadows, listed as endangered, filing multiple petitions with the Fish and Wildlife Service, including a new one this week.
Even so, it could be too late. “Now they can barely find it,” Greenwald said. “It may be extinct.”