Of the 136 butterfly populations studied, no one butterfly population has increased over the past 30 years.
The US butterfly population has dropped by 22% in 20 years, according to a study
The US butterfly population has declined by 22% over the past 20 years, studies show.
Walking around the Midwest today is a different experience than it was 30 years ago. That’s because the butterfly populations there are “sudden declines” and all 136 species examined in recent studies have either flat or reduced populations.
“We were expected to have had at least some species well over the last 32 years,” said the lead author of Michigan State University Wendy Louenberger, who was surprised by the findings.
Some of the most common species, such as the monarch, still exist, she said in a statement, but in a much smaller number, “it’s unlikely you’re likely to find a rare species either.”
“All of these are changes that have occurred during my lifetime and humility.”
What caused the decrease in butterflies?
The team whose survey was published was published in the peer-reviewed journal minutes of the National Academy of Sciences on August 4th, but did not assess the factors that led to the decline.
However, the time frame is parallel to the widespread use of the insecticide class “neonicotinoids,” introduced in 1994 and rapidly increasing in use since 2003. According to neonicotinoids, neonicotinoids are “one popular insecticide class in the United States.”
According to Michigan State University, the past decades have also seen changes in key weather variables due to global climate change.
The Butterfly Study, following another paper published in Science in March 2025, recorded a decline of 22% of national butterflies across the United States from 2000 to 2020. The study said that the main causes of decline include habitat destruction and arrier heat.
This current study includes more butterfly surveys than in March. Going back to the past 10 years, it is mostly collected by volunteers who have worked over 90,000 hours.
What did the new butterfly research find?
In a new study, researchers combined over 4.3 million observations of 136 butterfly species over the past 32 years to characterize changes in the biodiversity of butterflies in the Midwest.
The authors report that 59 of the 136 species had a plentiful decline during the study period. And for every 10 species that existed in the county in 1992, there are currently only nine species and 60 individuals.
The study also stated that butterflies are likely to have cascade effects across ecosystems. Because butterflies “provides countless ecosystem services such as pollination, herbivory (plant consumption by animals), prey and decomposition of other animals.
The Midwest has the highest density of butterfly surveys
The Midwest was the focus of the study due to the depth of local data.
Ellis Zipkin, a senior research author at Michigan State University, said: “Volunteer scientists use the same protocol every week and every year. Without valuable effort, we don’t know how butterflies run and what they can do to reverse the decline.”
Butterflies are the most commonly counted insects and are “possible poster species” about how other insects and animals differ to ecosystems, according to a statement from Michigan State University.
“Humans are more dependent on insects than we know,” Royenburger said. “We need to know how we can protect it before it’s too late.”
Contributions: Beth Wise, USA Today
