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.”

Bad news for other insects, Canadian butterflies?

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.

What’s causing the decline?

In this paper, Edwards acknowledged the data they have — counting butterflies — just doesn’t tell them why butterfly losses are so huge.

Pesticides, climate change, habitat loss are thought to be drivers of decline for many species.

Tseng said those threats are affecting butterflies not just in the U.S., but in Canada also, and many species live on both sides of the border. “And so I wouldn’t be surprised if we saw the same patterns [in Canada],” she said.

Jeremy Kerr, a University of Ottawa professor who studies butterflies and co-founded the eButterfly monitoring platform, said his own work in southern Ontario and the Prairies suggests butterfly declines in Canada are “probably pretty similar” to those in the U.S. He said species are also struggling with warming temperatures on our side of the border.

What can be done – including at home

Henry said the good news is that while butterfly populations can fall quickly due to threats like droughts, they can also grow quickly in response to interventions like habitat restoration, since most species can produce one to three new generations per year. She spoke to CBC News from Scatter Creek Wildlife Area in Washington, where she and colleagues were restoring prairie habitat and releasing captive-reared Taylor’s checkerspot caterpillars.

She said there are things people can do at home too, such as cutting pesticide use.

Both she and Kerr suggested planting your garden, or even your balcony, with species that butterflies need as hosts for their caterpillars (such as milkweed for monarchs) as well as flowers they need for nectar as butterflies.

Tseng said the new study also shows the importance of people volunteering their time to monitor wildlife through citizen science or community science apps.

“We’d love to encourage anybody out there at all to just, if you see a butterfly, take a quick photo and then put it onto iNaturalist or eButterfly or whatever platform is your favourite.”