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 earlier this month.
From California to Montana, and from New Mexico to Washington state, the populations of a majority of 450 butterfly species are dropping, according to observations by professionals and amateurs stretching back to the 1970s.
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, 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% drop in butterfly numbers in the Western United States over the past four decades.
Put another way: A butterfly spotter going to the same site every year saw about 25% 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% 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.
Art Shapiro, a biology professor at UC Davis who has collected data on California’s butterfly population for nearly five decades, says he’s seen the monarch’s decline firsthand as the manager of 10 butterfly study sites scattered throughout the state.
Last year, Shapiro recorded seeing fewer than 10 monarchs despite being in the field 200 days, a troubling figure considering there have been times in his career where he’s counted up to 30 monarchs in a single outing, Shapiro said.
He collects the data by walking predetermined routes along the study locations and recording his observations.
“I have not seen a wild monarch caterpillar myself for three years,” Shapiro said.
This year, he’s particularly concerned for the Painted Ladies species, which can breed by the thousands in years that the California desert sees rainy conditions, leading to a bloom of the type of plants the species feed on.
Years of dry winter weather make it harder for the butterfly species to produce offspring.
“In a bad year, like we expect this to be, they’ll be barely noticeable,” Shapiro said. “They can’t recolonize if there’s nothing to eat.”
Suzanne Clarke, who runs the Sonoma County Butterfly Alliance Facebook page and has been certified by the UC Master Gardener Program of Sonoma County —which trains volunteers to provide unbiased, science-based information to local home gardeners — says she uses the social media platform to help local residents make their home gardens more habitable to butterflies.
“Sometimes there are people who have a lot of caterpillars and no milkweed, so we send out an emergency request to either accept some caterpillars or lend some milkweed,” Clarke said, explaining that monarch caterpillars feed on the milkweed plant until they undergo metamorphosis. “We’ve started to build this community, which is nice.”
The information she shares on the account is an extension of presentations on butterflies she’s given at farmers markets and libraries over the past 20 years, an interest she first developed during her time as an elementary school teacher on the East Coast, when she would bring caterpillars from her yard into her classroom to teach students about the butterfly life cycle, Clarke said.
Her own home garden in Petaluma has been set up to host monarchs during their migration between the Mexico and Canada, as well as other types of butterflies. The garden includes a host of nectar plants that the adult butterflies can feed off, milkweed for the caterpillars and water, she said.
While she hasn’t observed a significant difference in the number of butterflies she’s seen on her property in the spring, those sightings have become more rare during the fall, Clarke said. She suspects years of back-to-back wildfires across Northern California, which can result in widespread smoky conditions, have driven the insects away, she said.
"Can we change our trees and environment, our habitat, to encourage (monarchs) to come back again?“ Clarke asked. ”There are people who are really wanting to reconstruct their conditions to the ones that monarchs like, to encourage them to come back during the winter.“
Besides monarchs, 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.
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.
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 maybe 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.
Staff Writer Nashelly Chavez contributed to this report.