A butterfly went extinct. That’s not the end of the story
Durrell Kapan propped himself on his elbows to inspect a shrubby plant. He searched for a sign that a pioneering experiment to restore something missing from the coastal dunes in San Francisco was working.
The caterpillars he was trying to find are so small, he said, it’s like they’re “living in a different world.”
More than eight decades ago, a mesmerizing butterfly with iridescent cobalt wings and stunning spots called the Xerces blue vanished from San Francisco. When it disappeared, it became perhaps the most famous insect to go extinct.
So this spring, the California Academy of Sciences, where Kapan is a senior research fellow, and its partners released dozens of butterflies from a closely related species in the Presidio, a park along the water at the north tip of San Francisco.
Kapan was looking for any offspring of those released butterflies, surrogates the team hopes will fill an empty spot in this ecosystem.
“This is a very powerful idea,” Kapan said, “the idea of a surrogate species for an extinct species.”
Amid a biodiversity crisis in which 1 million species may go extinct globally, humanity will increasingly face fraught questions: To restore ecosystems, should society replace animals that disappear? If so, what creatures should serve as surrogates for extinct ones? And could this become a roundabout way of bringing species back from extinction?
The butterfly experiment taking flight now in California may help answer some of those questions – even if not everyone agrees that trying to replace an extinct butterfly with another one is the best idea.
‘X’ is for extinction
Once found in the sand dunes that became San Francisco, the Xerces blue was a pollinator and food source – and may have even had a symbiotic relationship with the area’s ants.
Caterpillars of many related species provide ants with a sweet substance in exchange for guarding the soft-bodied larvae from predators. Some European species go as far as entering the ants’ nest and feeding on their young, which the ants tolerate for the sweet reward.
It’s a “baroque” relationship, butterfly researcher Robert Michael Pyle said. “It’s so complex it’s hard to even conceive of the ramifications.”
Development in the fast-growing city gobbled the Xerces’ habitat, driving it to oblivion and rendering it the first butterfly known to go extinct in North America due to human activity. The last was seen in the 1940s.
Three decades later, Pyle was on a train in England when, like a bolt from the blue, it occurred to him.
He had just listened to a lecture from a British entomologist about the decline of a butterfly species in the UK. The lecturer had suggested making that European species a symbol for British butterfly conservation.
Pyle, an American, thought of the Xerces blue. “We should make that our symbol for butterfly conservation in the U.S.,” Pyle said. The fact that the butterfly’s name began with an “X,” evoking “extinction,” didn’t hurt.
He went on to found the nonprofit Xerces Society for Invertebrate Conservation, turning it into a symbol for not just threatened butterflies, but all sorts of imperiled insects.
Something old, something new
Today, much of the Xerces blue’s old sandy haunts are bustling San Francisco neighborhoods. But an old U.S. Army post called the Presidio is now a national park site where managers have restored some of the lost dunes.
The Presidio Trust, a federal agency that manages the park, has repopulated the coastal landscape with turtles, newts and damselflies that once lived there. “We’ve had some successes with this,” Presidio Trust ecologist Lew Stringer said.
To find a Xerces stand-in, Kapan and his colleagues plucked DNA from the legs of Xerces specimens kept at the California Academy of Sciences and analyzed their genomes. Their analysis revealed that a relatively common butterfly called the silvery blue is a close relative.
So the team searched for silvery blues fluttering in habitats similar to the Xerces’ old foggy and sandy haunts in San Francisco. They found a match about 100 miles south in Monterey County. Both butterflies relied on the same plant, called deerweed, for laying eggs.
“It was a really good ecological match,” said Stu Weiss, a conservation ecologist who was a consultant on the project. “Probably the single most important thing for a butterfly reintroduction is to get the closest ecological match that you can.”
In April and May, researchers gently tucked some of the butterflies into coolers and fed them fruit-punch-flavored Gatorade on the ride to the city for release.
“It was really touching,” said Ryan Phelan, executive director of Revive & Restore, a nonprofit that partnered on the project. Holding a butterfly in the palm of her hand and placing it on a plant “felt like a religious offering.”
Something borrowed, something blue
The butterfly introduction required several organizations working together for years. One that decided not to partner on the project was the Xerces Society itself.
While the group that bears the butterfly’s name did not oppose the project, “we do not see it as a priority when there is so little funding for insect conservation,” said Scott Black, its executive director.
“We should invest limited funding in the protection of and habitat restoration for the butterfly species that are currently facing extinction rather than introducing a common species into new areas,” he added.
Proponents say the bill for the butterfly release wasn’t high – more than $70,000 for genome sequencing, ecological modeling and other work, according to Kapan. For Pyle, the Xerces Society founder, it feels like a missed opportunity. “I thought they were maybe missing out on a good thing,” he said of the group.
For years, Pyle backed the idea of introducing some near relative of the Xerces. Perhaps if scientists transported a genetically similar insect from a nearby location, natural selection in the new environment would nudge the introduced butterflies to be even more Xerces-like.
As he wrote in a 2000 essay, “extinction may not always have to be forever.”
Now scientists have the genetic tools to test how well the silvery blues adapt. “We might set it back on a trajectory that by natural selection would then enable it to evolve towards something that resembled the Xerxes blue,” Stringer said.
Weiss wonders how the surrogates will adapt to San Francisco’s fog. “That’s the really exciting part of the genetics – how natural selection hones the performance of organisms,” Weiss said. But other features, like the distinct spot pattern on the underside of Xerces’ wings, may be lost for good. “I’m not so sure about that” returning, he said.
‘Reknit the web of life’
The silvery blue introduction is similar to past conservation efforts, according to Ben Novak, Revive & Restore’s lead scientist. The group is involved in even more ambitious work using genetic advances to bring back the passenger pigeon and other extinct animals.
Wolves roaming Yellowstone today were originally from Canada, he noted. Peregrine falcons soaring over East Coast cities descend from transplants brought from elsewhere.
“Whether or not there’s any butterflies seen next year will be the real key thing,” he said. “Butterfly reintroductions are hard.”
For now, scientists in San Francisco are waiting to see what happens next.
In late May, Kapan was thrilled to spot a hairy caterpillar a quarter of an inch long nestled next to a flower on a plant where he had previously seen minuscule butterfly eggs – “so tiny that they are essentially smaller than a sesame seed.” But a later analysis of pictures of the caterpillar revealed it was not a silvery blue, but another butterfly species.
Kapan isn’t deterred. The researchers will look next spring to see if “a self-sustaining, fully established population” of silvery blues is beginning to take flight, he said.
This work isn’t “a ‘Jurassic Park’-style de-extinction project,” Kapan said. But for him, it is necessary for reviving lost ecosystems.
“There’s the direct need in many cases to do something similar for hundreds of species to reknit the web of life.”