It's difficult to count insects.
Even if scientists discover that many groups are declining, they have a hard time figuring out the scale of what is happening. Now, a groundbreaking new study offers the most comprehensive answers on the condition of adjacent US butterflies.
Twenty years later, the fleeting time it takes for a human baby to grow into a young adult lost 22% of the butterfly, researchers found.
Check out the butterflies in your area
It is known that 128 species in the study occur in New York, New York.
A chart of consecutive US population trends among the 128 butterfly species found in New York showed a decline in NY86 species, with 21 species showing almost a change, and 21 increased. 86 types 21 small changes 21 increase nationwide
Here are some you might see:
“They're a great opportunity to learn about the world,” said Ellis Zipkin, a quantitative ecologist at Michigan State University and one of the authors of the study, published Thursday in the journal Science. “Unless we change things, we're in trouble.”
Little understood and highly underrated insects play an oversized role in supporting life on Earth. They pollinate plants. They break down dead material and nourish the soil. They feed birds and countless other creatures in their food webs.
“Nature will collapse without them,” said David Wagner, an entomologist at the University of Connecticut.
Dr. Wagner, who was not involved in the new research, called it the “much-needed, Hercules assessment.” He praised the rigour of the study, saying the decline in butterflies, which reached 1.3% per year, is in line with other recent efforts to analyze global trends in the Earth's insect population.
Still, researchers did not have enough data to include some of the most dangerous butterfly species that have probably experienced some of the sharpest declines. And it is highly likely that the data is biased towards places where butterflies tend to appear. “Unfortunately for nature,” Dr. Wagner said the findings were “unquestionably a conservative assessment.”
The analysis was based on 12.6 million individual butterflies counted in almost 77,000 surveys across 35 surveillance programs from 2000 to 2020.
Butterfly Changes, 2000-20
Adjacent US data
That data came from volunteers who worked mainly on various programs and appeared at certain locations over the years on certain days and recorded all the butterflies they saw.
Other researchers specializing in mathematics and specialists in butterfly species and behavior have taken the raw data, harmonizing it, and created models that estimate the rich changes.
Of the 342 species that could draw conclusions, 33% showed a statistically significant decrease, and <3% showed a statistically significant increase. It decreased 13 times as it increased.
The number of American women with orange and black butterflies from coast to coast fell by 58%.
Hermes Copper, a rare butterfly found in San Diego County, plummeted 99.9%.
Even Cabbage White, originally from Europe and who discovered that he would munch vegetables as caterpillars, has been halved in being considered an invasive pest.
“It shocked me,” said Nick Haddad, a Michigan insect ecologist and research author. “If even the white cabbage is fading, oh my god.”
The study did not shed much light on how the monarch butterflies were doing, the authors said. The monarch recommended by the US Fish and Wildlife Service for federal protection in December shows a staggering decline in overwintering sites in Mexico and California. However, separate new data provided a lot of good news on that front. After hitting near record lows last year, the Mexican supervisor monarch has rebounded significantly this year's count, and was released on Thursday by the Mexican government and the World Wildlife Fund.
Scientists attribute a large increase in drought conditions along the travel routes of Eastern Monarchs traveling between the US, Canada and Mexico. But the western monarch of the Rocky Mountains, which is overwintering California, was almost record low on this year's count.
Why is the butterfly crashing? Experts condemn the combination of factors. There is habitat loss as land is converted for agriculture, development, climate change, and pesticide use. What's less clear is the extent to which each factor promotes a decline.
The study does not attempt to answer that question, but points to other findings from the Midwest and California. The class called neonicotinoids, which Europe largely banned in 2018, has proven to be particularly deadly.
While the public is often asked to plant native milkweeds to help the monarch caterpillars, a study in the Central Valley of California found that all collected samples were contaminated with pesticides. Even if the landowner says they don't use pesticides, it's true, suggesting that the chemicals were either drifted onto the plant or applied to the plant before purchasing.
The new findings show potential fingerprints from climate change. As the world warms, North American species move northward for more kinder conditions. When researchers compared the same species in adjacent regions, they found that northern populations were superior to southern populations in three-quarters of cases. Furthermore, two-thirds of species that showed an overall increase in the US are more Mexican regions than in the US and Canada, suggesting that they are growing in the north of that range. Without Mexican data, researchers cannot know what is happening there.
Researchers emphasized that the solution is at hand. Some people need to occur at a policy level, such as climate change tackling and pesticide regulation. However, in the meantime, they encouraged people to create habitat shelters for butterflies and other insects by planting butterfly flowers, shrubs and trees. One butterfly, along the Gulf Coast, appears to have increased its range as homeowners planted PassionVines and caterpillars eat them.
And remember those caterpillars, said Colin Edwards, ecological modeler for the Washington Fish and Wildlife Service and lead author of the study.
“When you spray something on a plant so that it doesn't eat things, the caterpillar is eating the plant,” he said. “They are butterflies.”
Methodology
The data in this article are from Edwards et al. (2025) and provided by researchers.
This study divides species into five categories. It is increasing, increasing, increasing, likely with little decrease, likely decrease, changing. Category reductions and increase species saw at least a positive or negative 10% change. Those with a tendency not statistically significant were classified as likely to decrease or increase. For the purposes of this article, presumably decaying species were grouped by decaying species of species, and the increasing categories included increasing species. Researcher data and code can be accessed here.
The lookup tool includes 235 types. Their ranges are based on Grames et al. (2024). The list of locations is based on US Census Bureau location and county parcel files.
The common names of species used in the lookup tool are based on a checklist from the North American Butterfly Association.
