Scientists brought to tears by huge loss of U.S. butterflies

A fluttering butterfly makes most people smile with delight — a reaction that makes them special among insects.

Some people love butterflies so much that, like birders, they look for and count them for fun. In the past two decades, those volunteers, along with researchers, have spotted and counted 12.6 million individual butterflies from 554 species as part of 76,000 surveys at 2,478 different locations across the U.S.

Now, a new study funded by the U.S. Geological Survey has finally compiled all that data — and found some bad news. Populations declined 22 per cent between 2000 and 2020, reports the new study published in the journal Science Thursday.

"I was really upset," said Collin Edwards, lead author of the new study. Edwards, who worked on the project during his postdoctoral research in quantitative ecology at the University of Washington in Seattle, added that he wasn't the only one devastated by the results.

"I know coworkers or coauthors who cried when they saw the manuscript with the final numbers."

Michelle Tseng, an ecologist and assistant professor at the University of British Columbia in Vancouver who wasn't involved in the study, had heard preliminary reports of the decline at scientific conferences, but initially couldn't believe the declines could be so big.

"So to see it in front of me, I was a bit shocked actually…. It's depressing," she said after reading the study. "That's massive."

Many of the more than 30 scientists who collaborated on the study had noticed declines among individual butterfly populations, but no one had compiled all the data until now.

"This is really the biggest and most comprehensive study of insects in certainly in the U.S., arguably in North America that we've done," said Edwards, now a data scientist at the Washington Department of Fish and Wildlife. "And, and so I think it really should be a bit of a wake-up call."

Erica Henry is a prairie ecologist with the Washington Department of Fish and Wildlife who studies rare butterfly conservation and who co-authored the study. She said that the loss of butterflies is a big deal, not just because they're beautiful and they inspire people, but also because of the role they play in ecosystems.

As caterpillars, butterflies transfer nutrients from plants up the food chain, while providing food for animals such as baby birds. As butterflies, they pollinate flowering plants.

But the potential impacts and implications go beyond that; what's happening to butterflies is likely happening to other insect species crucial to ecosystems, she said. "It could be a canary in a coal mine situation," she said.

"Where we're seeing these widespread declines with butterfly species … that's likely happening for other species as well."

Besides the overall butterfly population, the new study also looked at trends for individual species with enough data — about 350 of them. It found 13 times more species were declining than increasing. More than 100 species had lost more than half their population. And there was no obvious pattern to the declines – it seemed unrelated to things like location, the size of the species or the type of plants it relied on.