Butterflies are vanishing in the West. Scientists say climate change is to blame
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.
UPDATED: Please read and follow our commenting policy: