Large-scale analysis reveals 20% of butterflies in the US have disappeared since 2000

Butterflies are beloved creatures that inspire art and play an important ecological role, but according to new research featuring faculty members at Binghamton University, State University of New York, these cherished insects are disappearing at an alarming rate.

A new study published in Science examines butterfly data in the United States, and the results are troubling. Looking across 76,000 surveys, the study revealed that butterfly abundance fell by 22% between 2000 and 2020. To put it starkly: for every five butterflies in the U.S. at the turn of the century, there were only four remaining in 2020.

"This was the most comprehensive analysis of butterflies in the US and at such a big spatial scale," said Eliza Grames, an assistant professor of biological sciences at Binghamton University and co-author of the paper.

Butterflies are the most extensively monitored insect group in the United States, but most monitoring efforts have consisted of volunteer-based and expert science monitoring programs that are limited in geography and have focused on individual species.

This new study uses all available monitoring data—35 programs with records of over 12.6 million butterflies—to provide a clear picture of the state of butterfly species across the continental United States.

The study takes into account the variations in collection protocol and regions to produce comparable results for hundreds of species. Using data integration approaches, the team examined how butterfly abundances changed regionally and individually for the 342 species with enough data.

"Abundance" refers to the total number of individuals of a butterfly species within a given area. During the two-decade period examined, 33% of butterfly species showed significantly declining trends in abundance. Many showed extreme declines in abundance—107 species declined by more than 50%.

Grames' role in this nationwide study was to generate range maps for all butterfly species that fed into the analyses. This allowed the team to check whether observations of species were good identifications and should go into the model or if they needed to be checked for data quality cleaning purposes. The team could also see where each of these species could be found within the U.S. and examine spatial patterns.

"We didn't have maps for where many of the butterflies were," said Grames. "How do we know which records are good? A bunch of them come from iNaturalist, a citizen science platform where anybody can upload pictures of species. But sometimes people go to a butterfly house and start recording all of these tropical species in, say, Colorado, which throws off the data."

Part of those conservation efforts includes involving undergraduate students in assessments to gather data and determine how at risk a species might be. In Grames' Conservation Biology class, students are currently working on IUCN assessments for western skippers, including one of the most declining butterfly species, the Julia's skipper.

"Participating in this assessment has allowed me to apply what I've learned in class to real-world scenarios," said Clara Zook, a Binghamton University student working on the assessment for Julia's skipper with classmate Kieran Buchholz.

"It's empowering to know that our research could play a role in preserving this species," Buchholz said.

In addition to being beautiful and inspiring art, said Grames, butterflies also play a vital role in pollination, helping to pollinate food and flowers and contributing to the health of ecosystems around the world. This study could help drive important conservation efforts, such as prioritizing species for the International Union for Conservation of Nature (IUCN) Red List of Threatened Species and/or Endangered Species Act protection.

"We have much better data to go and say, 'You know, we should really consider these for federal protection.' So we can go in, conserve their habitat and—hopefully—they can rebound," said Grames.

Collin Edwards, the study's lead author, echoed those sentiments. "For those who were not already aware of insect declines, this should be a wake-up call," Edwards said.

"We urgently need both local and national-scale conservation efforts to support butterflies and other insects. We have never had as clear and compelling a picture of butterfly declines as we do now."

A second project, part of the same USGS group, is looking at the drivers of butterfly loss. A study in the Midwest has pointed to pesticides as a major driver, but there are different drivers across different regions of the U.S. For example, in the Southwest, there are concerns about drought, whereas in the Northeast, it's more about climate.

Grames said that highlighting what's happening with butterflies can help to provide a clearer picture of insect population decline overall.

"Insects are declining at rates of about 1–2% per year, which has come out across several studies," she said. "This was another study finding a supersimilar rate of decline, which really adds evidence to the growing picture of insect declines globally."