Nathan Brockman has been researching butterflies for years in Iowa.
“Insects have the ability to bounce back. They're really resilient creatures for the most part,” said Brockman, Reiman Gardens’ director of entomology at Iowa State University. “When what they need is there, they do really well.”
But with habitat loss, a warming climate and chemical use in agriculture, butterfly numbers across the country are declining.
From 2000 to 2020, butterfly abundance fell by 22% across about 554 species, a group of 33 authors from nonprofits, universities, and state and federal agencies found.
Brockman, who was not involved in the study, said he has seen the population decline anecdotally while studying butterflies around Iowa. He estimates that the number of butterfly species found in Iowa today is around 110, down from about 125 when he counted two decades prior.
“Decline in insects is something we've known for a while,” he said. “That's what I've seen, without even sitting down looking at the data.”
More than just butterflies at risk
Although the researchers – who collaborated across the country – saw a 22% decline in the total number of butterflies, they found that at the species level some butterfly populations increased. Still, 13 times more species declined than increased in population between 2000 and 2020.
The research also found that two-thirds of the species examined showed declines of 10% or more. Abundance of some species shrunk by up to 95%.
The researchers pulled data from more than 76,000 surveys, using 12.6 million records of individual butterflies from different monitoring programs across the country.
“I think that widespread declines are really concerning and probably indicative that other things besides butterflies are also declining,” said Elise Zipkin, director of the Ecology, Evolution and Behavior program at Michigan State University.
Zipkin, who collaborated on the data analysis portion of the study, said biological loss across the board could represent the beginning of another mass extinction event.
“The biodiversity loss that we're seeing rivals that of the five mass extinctions that we've seen in the past,” Zipkin said.
Daniel Marschalek, an associate professor in the Biological and Clinical Sciences Department at the University of Central Missouri, said this study – both in the number of species and size of the region examined – was one of the first of its kind in the U.S.
Marschalek, who is an author on the paper, said butterflies have been used for assessing habitat and environmental health for many years.
“Initial studies showed that there's a pretty good pattern between insect or butterfly numbers and the species richness and the habitat quality,” he said. “It's been a way to kind of track over time what's happening in our environment.”
Before this study’s publication, Marschalek said that studies limited to the Western regions of the country found steep population declines in butterflies and insects across the board.
But with this study, the researchers determined that butterfly abundance has dropped about 1.3% yearly nationwide since 2000.
“That 1.3% might not sound that big and you might not notice it from one year, to year two or three. But when you start looking over a 20-year period, those really start to compound – kind of like interest in an account – you start to see a pretty substantial decline,” Marschalek said.
Marschalek added that the decline in U.S. butterfly populations could mean the environment is slowly becoming less suitable for life across the country.
“It should be really alarming,” Marschalek said. “What we're doing really needs to flip around pretty quickly, otherwise we are putting a lot of species, including humans, at risk.”
Wayne Thogmartin, a research ecologist with the U.S. Geological Survey, said that the decline of butterflies and other pollinators could lead to human health risks down the line.
“I think that this is just a symptom of a larger concern about how we're failing to take care of the natural world around us,” said Thogmartin, another investigator involved in the study. “It's gonna come back to bite us.”
Butterflies can bounce back – but human behavior must change
Fortunately, Thogmartin said, insects have the reproductive capacity to increase abundance “very quickly,” if the right conditions are in place.
“For those species that have declined so quickly, so deeply, it's going to take specific attention to those species to counteract those declines,” Thogmartin said. “Just creating a more natural environment, maintaining and conserving the natural environments that we have is probably a good first step, and restoring lost habitat is essential as well.”
Marschalek said that although it is possible for the populations to rebound, it would take “large-scale planning” and a commitment from individuals to change current land use practices.
He said individuals can help by growing native plants and reducing the frequency of mowing yards.
“I think that butterflies could come back now, even with climate change, [because] we're past the point of no climate change,” Zipkin said. “But if we remove some of those anthropogenic pressures that we have, I'm very optimistic.”
This story is a product of the Mississippi River Basin Ag & Water Desk, an independent reporting network based at the University of Missouri in partnership with Report for America, with major funding from the Walton Family Foundation.