Between 2000 and 2020, the number of butterflies in the United States fell by 22%, according to a new study funded in part by the Midwest CASC. The researchers calculated this alarming decline from over 76,000 surveys and 12.6 million records of individual butterflies combined from 35 different monitoring programs across the country. There were enough records for the researchers to calculate population trends for 342 of the 554 total species in the dataset. 

Butterflies are essential pollinators and, as caterpillars, are important food sources for many types of birds. They are also the most widely surveyed group of insects. Despite this, this study, published in the journal Science, is the first to pull together data from various monitoring programs to analyze nationwide trends. Many of these monitoring programs rely on citizen science efforts, so understanding the full scale of the butterfly decline wouldn’t have been possible without community involvement. The researchers found that about half of the species had populations that declined by more than 42% over the twenty-year period, while 107 species declined more than 50%, and four species more than 99%. Only nine species in the study experienced population increases.  

Butterflies play a key role as pollinators for both wild and agricultural plants – including many flowers that bees don’t visit. Yet, habitat loss, climate change, and pesticides are driving their widespread declines. The study’s authors emphasize that, despite these challenges, butterflies have short life cycles which allows for rapid population growth and recovery – provided the right conditions and strategies are in place.  

This research was funded in part by the Midwest CASC project: “Evaluating the Role of Climate on Midwestern Butterfly Trajectories, Monarch Declines, and the Broader 'Insect Apocalypse.'"