Nationwide study finds butterflies to be in trouble

Butterflies are in serious decline, according to a comprehensive study that analyzed a huge data set collected throughout the United States.

Abundance of the beloved insects declined 22% in the first two decades of the 21st century, according to the work published Thursday in the journal Science.

“What we saw is really stark,” said Cheryl Schultz, professor of conservation biology at Washington State University’s Vancouver campus. “When you look at all species, one in three have declined by more than 50% in the last 20 years.”

Out of the 342 butterfly species the study looked at, 107 dropped by a rate of 50% and 22 species suffered declines of 90% or more.

Schultz, a senior author of the study, said the special place butterflies occupy in the human imagination made the work possible. For better or worse, people gravitate toward certain species. For example, large mammals like elephants and polar bears — what scientists call charismatic macrofauna — get a lot of attention from humans.

Butterflies are clearly one of the superstars of the insect world.

“I think of butterflies in the way of the charismatic microfauna,” she said.

In short, people so love the colorful, fluttering pollinators that they have volunteered to participate in tens of thousands of scientist-led monitoring projects across the Lower 48 states.

“The ability to work with these data comes from thousands and thousands of volunteers out walking, counting and identifying butterflies,” Schultz said.

But those projects have been geographically limited, mostly looking no further afield than a specific state and often drilling down on a much smaller footprint. The authors of the study collected all that information into a single dataset and used it to identify abundance trends.

While the results are mostly bad, about one-quarter of the butterfly species in the study expanded in part or all of their range. Some regions of the country are doing better than others. For example, the Pacific Northwest saw an overall increase in butterfly abundance. That was largely attributed to the California tortoiseshell that is prone to population explosions. When the authors excluded the small orange and black species from the study, they found butterflies in the Northwest declined by about 2%.

The study also showed individual species tend to be in better shape in the northern portions of their range compared to areas further south. Similarly, the Southwest region saw the greatest declines, followed by the Mountain Prairie states that can also be hot and dry.

Previous work has pinned butterfly declines on climate change, widespread pesticide use and habitat loss. Efforts are underway across the country to help reverse the loss of habitat. That ranges from restoration of large native prairies to people converting their yards and other property from lawns and nonnative ornamental shrubs to native flowers.

“Butterflies need host plants on which to lay eggs, wildflowers on which to feed, a refuge from pesticides, and sites to overwinter,” said Scott Black, director of the Xerces Society and study co-author, in a news release. “There is hope for these animals if we focus on providing habitat for butterflies across all landscapes, from cities and towns to agricultural lands to natural areas.”

Schultz agreed there is reason for optimism. She has worked on an effort to recover Fender’s blue in Oregon’s Willamette Valley. The small butterfly is found only there and was once thought to be extinct. It was listed as endangered in 2000. Following a partnership between federal and state agencies, private landowners and conservation organizations to restore prairie habitat, Fender’s blue was upgraded to threatened in 2023.

“It was so encouraging to see the number of people engaged in thinking about how to recover that butterfly, and it’s working,” she said. “The Willamette Valley is more than 95% private land. If we can recover a butterfly in a landscape that is almost all private, we can do that in a lot of places.”

Schultz said people can help butterflies by restoring habitat, even if it’s just small patches in their yards or on the edges of parks and public places, and by limiting the use of pesticides.

“There is an incredible opportunity to start replenishing habitat in and around the places we live. We can make a huge difference.”

Barker may be contacted at ebarker@lmtribune.com.