Butterflies and other pollinators are essential to the production of a large number of crops and other plants. According to the U.S. Department of Agriculture, about three-quarters of flowering plants need pollinators to reproduce, as do about a third of food crops. The insects that provide these services are in decline, however, and a new study shows just how stark that decline is.

Researchers at Binghamton University in New York State recently compiled data from dozens of citizen science programs, with records of 12.6 million butterflies, to see how butterfly population levels changed between 2000 and 2020 in the United States. According to the findings, published in the journal Science, there was an overall 22% decline during that time period. The researchers say this likely means steps need to be taken soon to stop the downward trend.

Collin Edwards, the study’s lead author, says, “For those who were not already aware of insect declines, this should be a wake-up call. 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.”

The population picture came from more than 76,000 surveys done by 35 citizen science programs throughout the U.S., involving 554 recorded species. In addition to the broad 22% decline, the USGS-funded study found that 33% of the species had significant declines, with 107 declining more than 50%. In all, there were 13 times as many declining species as increasing species.

Eliza Grames, study co-author and assistant professor of biological sciences at Binghamton University, says, “Insects are declining at rates of about 1-2% per year, which has come out across several studies. This was another study finding a super similar rate of decline, which really adds evidence to the growing picture of insect declines globally.”

The researchers write that their findings suggest habitat restoration, species-specific interventions, and reducing pesticide use are likely needed to stem butterfly declines.

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