Michiganders venturing out on a hike this spring might be excited to be feeling sun rays after a dark, frozen winter. During that journey, however, the tiny, winged companions they normally encounter might not be there this year.
A new study published in the journal Science has found that total butterfly abundance has fallen in almost every major region of the continental United States from 2000 to 2020. The decrease in butterflies wasn’t minor — 22% of the 554 recorded butterfly species decreased during that time frame.
Researchers found that butterflies are declining at a species level on a broad scale. Over the course of the study, 33% of individual butterfly species exhibited significant declining trends in abundance, with only 3% of species increasing. Declines were most severe in the Southwest U.S. region, which is consistent with previous research finding hot and arid climates have faced disproportionate declines in butterflies.
The study utilized data from 35 butterfly monitoring programs across the country, compiling 12.6 million reports of individual butterflies from 76,957 surveys. One of these monitoring programs can be found in the mitten state at Michigan State University.
Nick Haddad, professor of ecology at Michigan State University, knows a little something about butterflies. He’s studied them for about 30 years.
Haddad contributed to an Ohio data set that was used in the study. He said the research published earlier this month was unique in that it utilizes regional, state, and local data to make inferences about the continental U.S.
“We wondered how can we do this kind of analysis for the whole country, and do we find consistent patterns across them,” Haddad told Michigan Public.
He said the results have made a startling inference on the decline of an important insect.
“The butterflies are declining,” Haddad said. “We’ve lost a quarter of all butterflies, and that in itself is distressing, but scarier still is that the trend is downward and there’s no clear end to the decline.”
Haddad said the dataset, while broad, lacked some representation from different areas around the country, limiting the data. For example, the Chicago area had many data sets, but North and South Dakota both had smaller pools of data.
Why are butterflies important?
Elise Zipkin is a professor of ecology at Michigan State University who also directs the school’s Ecology, Evolution, and Behavior Program. She worked on the analysis of the data and helped to write the research paper. Zipkin said butterflies have essential jobs for the environment.
“People don't realize that butterflies, while they are definitely beautiful and great to look at, they also serve really important ecological roles,” Zipkin told Michigan Public. “They help ecosystems with turning over dead, decomposing matter, energy cycling. They're also [a] really important food source for a lot of other species, including birds.”
In addition to serving as a food source and aiding in energy cycling, butterflies are pollinators. As they feed on the nectar of various flowering plants, they move pollen from one flower to another, helping those plants reproduce. Previous research has shown that butterflies have contributed significantly to pollution in ways that traditional pollinators, like bees, do not.
What’s causing the decrease?
The research did not attribute a specific cause for the decline in butterfly populations, but it did mention that butterflies are facing multiple broad threats. They’re facing habitat loss, climate change, and pesticide use.
Insecticides have been found to be the leading cause of butterfly deaths in the midwestern U.S. and California. Zipkin said insecticides like neonicotinoids that are applied to seeds are particularly harmful.
“What happens is when you plant those, so something like corn and soybean, which are grown a lot in the Midwest, they leach into the soil, and then that can be uptake by a lot of other plants, and that essentially gets into the plants and then kills all the insects,” Zipkin said. “So it's likely some of the reason that we see the declines in butterflies.”
Haddad said that butterflies’ declining trend may be indicative of a larger insect population decline, but more study is needed.
“Butterflies are indicators for the rest of the insect world, and insects comprise much of the diversity of life on Earth,” Haddad told Michigan Public.
Butterflies are unique and colorful, making each species distinct from one another. Haddad said that butterflies are relatively easy to categorize when making observations about nationwide trends, but that might be more difficult when looking at other insects, like flies, that are not so easily distinguishable. He said he hopes that by utilizing technological tools, like cameras and artificial intelligence, researchers can begin to start tracking trends in other insects to determine if a larger decline is ongoing.
Despite the loss of butterflies in recent decades, Zipkin said there’s still hope for the insects, particularly due to their breeding habits.
“I know sometimes these kind of results can make us feel really down about the state of butterflies,” Zipkin said. “But the good news is that under the right conditions, butterflies can really recover. So, unlike mammals or other kind of vertebrates, where the parents only produce one or a few individuals, in the right conditions, the butterflies can really produce many, many individuals in a year.”
The study encouraged digitizing historical butterfly records to offer new insights from decades' worth of data. According to the study, 90% of insect collections are not yet available for analysis.
Haddad said that Michiganders can also help slow the decline by limiting their pesticide use and planting native plants that caterpillars and butterflies eat, like Monarch City milkweed or flowering plants like verbena and marigold.
