Humans wiped out a native San Francisco butterfly. Now another species is filling its ‘big blue shoes’

For decades, conservationists have been restoring the biodiversity of San Francisco’s coastal dunes. But a key piece of the puzzle was missing — until now. 

The Xerces blue butterfly, which serves as both pollinator and prey in the ecosystem, has been extinct since 1943. 

So scientists identified the species’ closest living relative, the silvery blue butterfly. And this month, they released dozens of them into Presidio National Park.

“This is a historic occasion,” entomologist Durrell Kapan, a California Academy of Sciences senior research fellow, told As It Happens host Nil Köksal.

“[It’s been] over 80 years since the Xerces blue butterfly flew in the Presidio National Park. And now standing in Xerces’s big blue shoes, as I like to say, is this species.”

What happened to the Xerces?

Xerces blue butterflies once made their home among the sand dunes of what is now western San Francisco.

But colonization, and the ensuing development of San Francisco’s Richmond and Sunset neighbourhoods, destroyed their habitat and wiped them out.

They are believed to be the first American butterfly species to become extinct due to habitat loss — something Kapan calls an “ignominious fate,” and one that’s symbolic of a wider problem.

“Insects are suffering huge declines worldwide,” he said. “What that means is that all that great work that insects do, including feeding all the things we love, like birds, is not being done.”

For 30 years, the Presidio Trust and the Golden Gate National Recreation Area have been working to restore the biodiversity of San Francisco’s dunes at Presidio National Park, the site of a former U.S. military base. 

That work, Kapan said, created conditions in which the butterflies could be reintroduced.

But with no living Xerces blues remaining, he and his colleagues turned to the California Academy of Sciences’ massive collection of specimens, using genetic sequencing to better understand the Xerces blue genome. 

They determined that a group of silvery blues in Monterey County, about 160 kilometres south of San Francisco, could successfully fill the ecological gap.

Wildlife experts then collected dozens of silvery blue butterflies from Monterey County, marked them for future identification and transported them to San Francisco. 

So far, they’ve released 43. Already, Kapan says, the butterflies have laid eggs in their new home, and at least one has hatched. 

“We are so pleased that 30 years of habitat restoration in the Presidio has recreated the natural conditions necessary to support the silvery blues,” Jean Fraser, CEO of the Presidio Trust, said in a press release.

“This return is another example of how humans and wildlife don’t just co-exist, we thrive together in the Presidio.”

What role do they play in the ecosystem?

Both species of butterfly, Kapan says, are pollinators of deerweed and other dune plants. 

They are prey for lizards, birds and spiders — “which, you can imagine, is a little bit of a challenge for our butterflies when we let them go.”

And like most blue butterflies, they have a symbiotic relationship with ants. The butterfly larvae produce a sweet secretion, which ants feed off, as if suckling from a cow. In exchange for the tasty snack, the ants protect the larvae from predators and parasites.

Ryan Norris, an ecologist at the University of Guelph who has been involved in repopulating Ontario’s endangered mottled duskywing butterflies, welcomed the news that blue butterflies are once again flying in western San Francisco. 

“Any time a species is reintroduced successfully to a new habitat, I think it’s great news, because it signals that a habitat … is ready to receive species that are appropriate for it,” he said. “It’s a signal of good health.”

He commended the team for tracking down the extinct butterfly’s closest cousin, and using it in their repopulation efforts.

“I think it was a great idea,” he said. “I applaud them for their efforts.”

What’s next?

Norris and his colleagues released hundreds of mottled duskywings at the Pinery Provincial Park near Grand Bend, Ont., in 2021. So far, he says, they appear to be doing well. 

But determining whether the project is a success, he says, is a long game — one that requires continued research over the course of at least a decade, and the funding to do it.

“Butterfly populations tend to be so volatile — like, they go up and down from year to year — that you kind of need a big range of annual climate conditions to really feel secure in what you have,” he said.

That work is just beginning for the team monitoring the new Xerces population. 

Right now, Kapan is busy monitoring egg and larval development — which, for him, means sitting among the dunes for hours on end, scanning deerweed with binoculars for tiny butterfly eggs, and waiting for them to hatch. 

“This is really only the first step,” Kapan said. “Our team is ready to work on this for years to come.”

With files from The Associated Press. Interview with Durrell Kapan produced by Katie Geleff and Leslie Amminson