Butterflies may be among the most beloved of all creatures, routinely deified in art and verse, but they are in alarming decline in the United States with populations plummeting by a fifth in just the past two decades, according to the most comprehensive study yet of their fortunes.
The abundance of butterflies in the US slumped 22% between 2000 and 2020, the new analysis of more than 76,000 mostly regional surveys, published in Science, found. For every five butterflies fluttering daintily around at the start of the century, just four remain today.
“It’s such a short timespan to lose this many butterflies, it’s very sobering,” said Eliza Grames, a biologist at Binghamton University and study co-author. “This is a wake-up call – people should be really concerned about this rate of loss and what we stand to lose. People like butterflies but it’s going to take a lot of work to turn things around.”
Grames said the drop in butterfly numbers in the US is strikingly similar to the overall estimated average rate of insect loss, of about 1% to 2% a year, that is occurring in surveyed sites around the world. This so-called “insectageddon” threatens the foundations of food webs and ecosystems and has ominous implications for our food supply given approximately a third of all crops depend upon pollinators such as butterflies and bees.
“This was another study finding a super similar rate of decline, which really adds evidence to the growing picture of insect declines globally,” Grames said.
The new research drew together more than 30 scientists to pore over reams of data detailing sightings of butterflies across the US. More than 340 species had enough information on them to ascertain their population trends.
This work didn’t identify exact causes for the declines, although scientists have been clear that habitat loss, pesticide use and the climate crisis are the main culprits for insect losses, with other problems such as light pollution affecting fireflies and moths in particular.
For butterflies, the threats vary by region – in the more arid US south-west, drought worsened by global heating is causing butterflies to desiccate and for host plants to wither. In the agricultural heartland of the midwest, meanwhile, the rampant use of insecticides on fields is the leading cause of butterfly mortality.
While the loss of insects has huge consequences for humanity, many people are still squeamish about them or care little for their fate. Butterflies are a rare exception to this, with volunteers routinely helping raise the creatures from caterpillars or planting milkweed to help spur monarch butterflies, famed for their vibrant, long-distance migrations but last year listed as endangered for the first time in the US.
“People have a fondness for butterflies that they don’t have for other insects,” said Grames. “If your average person with a backyard knew they could do something to help butterflies, they would. It’s almost a gateway to think about ecosystem health in general.”
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Habitat restoration, action on the climate crisis, and a recognition that insects are valued wildlife and not just pests will all help butterflies, Grames said. “Butterflies aren’t as efficient at pollination as bees, or cycle nutrients as much as grasshoppers, but they are still important. They inspire art and literature. We are attracted to them,” she said. “Our connection to them helps us think about our connection to the world around us.”
Still, some butterflies might be beyond rescue in certain places. Several species have declined by 95% or more since 2000, the new research found, including the tailed orange, the Mitchell’s satyr, the painted crescent and the Hermes copper. One species, the Florida white, has essentially vanished from the survey record in the past 20 years.
Art Shapiro, a leading butterfly researcher at the University of California, Davis, has conducted one of the longest-running surveys in the world, having studied the same stretch of California for butterflies since the 1970s. Shapiro, another co-author of the latest research, sees far fewer species of butterflies now then he did then.
“At the time it had never occurred to me that butterflies might be going the way of the dodo or the dinosaurs,” Shapiro said. “Now, at age 79, I find myself wondering which of us will depart this Earth first. Not a pleasant thing to contemplate.”
