Brian Cassie has been counting butterflies in Massachusetts for decades. He helped create Mass Audubon’s butterfly atlas in 1986 and founded the Massachusetts Butterfly Club shortly afterwards.
He fondly remembers fields full of fluttering insects: hundreds upon hundreds of orange European skippers, delicate beige frosted elfins and polka-dotted hairstreaks.
Now, he says, he’s lucky to see a handful of European skippers at the height of their summer season. He found just one frosted elfin last year. And he worries the hairstreaks may have disappeared from the Massachusetts mainland altogether.
“I haven’t seen any of them in four years. Not a single one,” he said of the hairstreaks. “Butterflies that I used to see 200 or 300 or 400 of in a big field of milkweed, they’re all completely gone.”
Cassie’s observations are now included in a landmark study published Thursday in the journal Science. The research finds butterflies are declining rapidly across the contiguous United States, including Massachusetts. The data showed both species diversity and overall numbers are in decline: Nationwide, the authors estimate butterfly abundance fell by 22% between 2000 and 2020.
“It’s pretty shocking, really, that we’ve lost that much biodiversity in such a short time,” said Eliza Grames, a conservation biologist at Binghamton University in New York and one of the study authors.
The research aligns with other studies in recent years that have reported an overall decline in insect populations and biodiversity globally, a phenomenon often referred to as the “insect apocalypse.”
Insects and other invertebrates serve critical functions in many of the world’s ecosystems — famed Harvard entomologist E.O. Wilson called them “the little things that run the world.” Grames said butterflies have value beyond their beauty; for instance, they pollinate flowers and provide food for birds.
According to authors of the new study, it’s the first report to look at trends in butterfly population and diversity across the country. It drew data from more than 75,000 smaller, local surveys, conducted in large part by volunteer groups like the Massachusetts Butterfly Club.
Uli Lorimer, director of horticulture at the Native Plant Trust, called the research an important addition to the body of butterfly knowledge.
Lorimer, who was not involved with the study, said documenting the decline of butterflies may also help draw attention to the plight of insects deemed less delightful, like beetles and moths.
“Butterflies have a lot of charisma,” he said. “They have a way to draw connections to nature with people that perhaps other insects don’t have. For that reason, I think [the study] is actually quite impactful.”
Butterflies’ popularity is a chief reason this research was possible, according to study authors. Scientists and enthusiasts have been studying butterflies for centuries, often collecting local data for decades or more. One famous example is Art Shapiro, a professor at the University of California, Davis, who’s studied butterflies at the same sites every two weeks since 1972.
As the most-studied insects, butterflies can offer a window onto the overall health of an ecosystem.
“Butterflies might be a little bit like the canary in the coal mine, saying something is not right in the environment,” said study co-author Elizabeth Crone, an ecology professor at UC Davis.
The study pointed to three main drivers of the decline: pesticide use, climate change and habitat loss. Declines were most severe in the Southwest, where increasing heat driven by climate change is a likely factor, said Crone.
“ In the Southwest, one of the biggest changes is increasing drought,” she said. The drought is damaging or killing the plants that butterflies eat “as well as potentially stressing the butterflies.”
While the Northeast also suffered losses in butterfly diversity and abundance, the declines were less extreme than in some other regions of the country, according to the study.
Researchers attribute this to several factors, including the lower use of pesticides in the Northeast as compared to regions with widespread industrial agriculture; butterflies’ ability to survive wet conditions better than arid weather; and their ability to expand their range northward to adapt to a warmer climate.
Some butterflies are even increasing their numbers in the Northeast, as warmer winters allow some species to expand their range or lay eggs twice each each year.
One of the “climate change winners” is the tiny, rust-colored Zabulon skipper, which has increased its numbers in Massachusetts, said Crone. She said it offers hope that butterflies can adapt to changing landscapes and ultimately recover.
“Ecology always surprises us,” she said.
Unlike many other threatened animals, “butterflies have the potential for rapid population growth under the right circumstances, making species recovery possible — even from very small population sizes,” according to the study.
Cassie, the Massachusetts Butterfly Club founder, agrees. His front yard in Foxboro attracts an astounding 70 species of butterflies in an area about the size of a smallish party tent. He said anybody can help butterflies by limiting — or avoiding — pesticides in the garden, and planting native flowers like butterfly milkweed in the yard.
”These tiny little oases make a giant difference for butterflies,” he said.
This article was originally published on WBUR.org.
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