Every year around the Fourth of July, groups of volunteers fan out across Nebraska prairies, walking the same paths to count every butterfly they can find.
The data they collect has become one of the most important tools scientists use to track a quiet environmental decline.
A 2025 study published in the journal Science found that the total butterfly population in the United States fell 22% between 2000 and 2020.
The study drew heavily on decades of count data gathered by volunteers through the North American Butterfly Association's (NABA) July Fourth count, the same kind of count held annually at Lincoln's Pioneers Park.
"The paper was largely based on the NABA count data for the last 20 years, because it used counts that had existed for 20 years," said Jeffrey Glassberg, president of the North American Butterfly Association and co-author on the study.
Glassberg founded NABA in 1992 to give butterfly enthusiasts an alternative to netting and killing specimens, which was the standard method of identification before close focusing binoculars became available.
The organization’s July Fourth counts, modeled off the National Audubon Society's Christmas Bird Count, is now the largest, longest-running volunteer butterfly monitoring program in the world.
The butterfly count at Pioneers Park has run every summer since 2001. Ted Burk, a biology professor at Creighton University who has studied prairie butterflies for 28 years, helps lead it.
"It's an event that's open to the public," Burk said. "They can do it just for a nice walk in the prairie, or they can help collect serious data. They can introduce their kids to nature, just have a fun day out. It's as much educational as it is scientific."
On a count day at Pioneers Park, volunteers get a brief morning orientation on basic butterfly biology and identification before walking a specific route for two to three hours, keeping count of every butterfly they identify.
The results are then submitted to NABA's national database, which is used in peer-reviewed scientific papers.
Despite the national decline, Burk said Pioneers Pak itself hasn't shown a consistent drop in numbers over the years, a pattern he attributed to the site's high-quality prairie habitat.
"We tend to go out and do these counts in places which are high-quality habitats," Burk said. "Even if we have a high-quality place like Pioneers Park and we don't see declines there because the habitat there is in good shape, it is still going into the big database, which allows you to tease out where things are not doing so well."
Both Burk and Glassberg pointed to habitat loss as a driver in the decline of butterfly numbers. More than 95% of the original tallgrass prairie that once covered the region has been converted to agriculture, Burk said.
In the past two decades, both scientists said neonicotinoid pesticides have likely driven the most rapid losses, along with the broader effects of climate change.
Burk said sustained temperatures with heat indexes above 100 degrees can push even heat-loving butterflies into hiding, and extreme heat can kill monarch caterpillars.
Monarch numbers did look strong through the early part of the season, Burk said, but it will take another generation or two to know how the heat wave ultimately affected them.
A July 3 count at the Niobrara Valley Preserve in north-central Nebraska, reported on the blog Nebraska Lepidoptera, showed that uncertainty.
Volunteers counted 28 species, one more than the previous year and in line with the 10-year average, but only 150 individual butterflies, well below the 10-year average of 194.
They still counted several state-tracked species, including the Regal Fritillary and the Monarch. Regal Fritillaries are a particular focus for Nebraska researchers. The large, orange prairie specialist has disappeared from much of its historic range, which once stretched from the Rockies to the Atlantic. Eastern Nebraska, along with parts of Kansas, Iowa and Missouri, now holds one of the last habitats for the species.
"It's been extirpated from probably 90% of its original range," Burk said. "We always are very anxious every year to see how the Regal Fritillaries are doing. We are kind of the last stronghold."
Both Glassberg and Burk said the average person can help, even without access to large areas of prairie.
Planting native plants, milkweed and nectar plants can support caterpillars and butterflies.
"If you want wild indigo dusky wings, then you can plant wild indigo plants," Glassberg said. "So, you can learn what to plant and you'll get different butterflies."
NABA also runs a certification program for home butterfly gardens that Glassberg said has helped spread the practice among neighbors.
"They're just marvelous creatures," Burk said. "The late E.O. Wilson, a very prominent entomologist, said that every species is like a unique work of art and to lose a species is like losing a Ruben or a Picasso. It's a unique creation that can never really be brought back."