Bye-bye butterflies? Insects are in 'precipitous decline' in Midwest.
Out of the 136 species of butterflies’ populations studied, not a single one increased over the past 3 decades.
Taking a walk in the Midwest today is a different experience than it was 30 years ago. That's because butterfly populations there have been in "precipitous decline," with all 136 species examined in a recent study either flat or declining in population.
“We expected to find that at least some species had done well over the past 32 years,” said study lead author Wendy Leuenberger of Michigan State University, who was taken aback at the findings.
Some of the most common species like monarchs are still present, she said in a statement, but in far fewer numbers, and "you’re less likely to spot rare species as well."
"These are all changes that have occurred during my lifetime, which is humbling.”
What caused the butterfly decline?
The team, whose research was published Aug. 4 in the peer-reviewed journal Proceedings of the National Academy of Sciences, did not evaluate the drivers of the decline.
But the time frame is parallel to the widespread use of the insecticide class "neonicotinoids," which were introduced in 1994 and rapidly increased in use after 2003. According to the Natural Resources Defense Council, neonicotinoids are "the single-most popular insecticide class in the United States," and are used on crops, lawns, gardens, golf courses and in flea and tick pet treatments.
The last several decades have also seen changes in key weather variables because of global climate change, according to Michigan State University.
The butterfly study follows another paper published in March 2025 in Science, which documented a 22% national butterfly decline across the United States from 2000 to 2020. That study, which Leuenberger also co-authored, said the chief causes of the decline included habitat destruction, a drier and hotter climate because of climate change and insecticide use.
This current study includes more butterfly surveys than the March study, by going back a decade further ‒ most collected by volunteers working more than 90,000 hours.
What did the new butterfly study find?
In the new study, researchers combined more than 4.3 million observations of 136 butterfly species over the past 32 years to characterize changes in butterfly biodiversity across the midwestern United States.
The authors report that 59 of the 136 species declined in abundance over the study period. And for every 10 species and 100 individuals present in a county in 1992, there are now only nine species and 60 individuals.
The study also said that widespread declines among butterflies are likely to have cascading effects across ecosystems, because butterflies "provide myriad ecosystem services, including pollination, herbivory (the consumption of plants by animals), prey for other animals, and decomposition."
Midwest has highest density of butterfly surveys
The Midwest was the focus of the research, because of the depth of local data.
"We are lucky to be working in the midwestern U.S., an area with the highest density of butterfly surveys of anywhere in North America,” said the study’s senior author Elise Zipkin, also of Michigan State University. “Volunteer scientists use the same protocols week after week and year after year. Without their invaluable efforts, we would not know how butterflies are faring and what we can do to reverse declines.”
Butterflies are the most commonly counted insects and "a likely poster species" for how other insects and animals crucial to ecosystems are faring, according to a Michigan State University statement.
“Humans rely on insects more than we realize,” said Leuenberger. “We need to figure out how we can protect them before it’s too late.”
Contributing: Beth Weise, Paste BN