93-year-old butterfly’s DNA confirms first case of insect extinction caused by humans in the U.S.

CHICAGO, Ill. — The DNA of a nearly century-old butterfly appears to be the smoking gun in the first case of human-led insect extinction in the United States. The Xerces blue was last seen flapping its iridescent periwinkle wings in San Francisco in the early 1940s.

Experts generally accept that the species is extinct today. The 93-year-old DNA is now confirming that butterfly is the first American insect species destroyed by urban development. Until this study, questions have remained about whether the Xerces blue was really a unique species or just a sub-population of another common butterfly.

Analyzing the DNA in museum collections, researchers at the Field Museum in Chicago found that the insect’s DNA is unique enough to call it a separate (and now extinct) species.

The findings, published in the journal Biology Letters, confirm that the Xerces blue really did go extinct and the research team says that insect conservation is something we have to take seriously.

A collections drawer of extinct Xerces blue butterflies. (Credit: Field Museum)

“It’s interesting to reaffirm that what people have been thinking for nearly 100 years is true, that this was a species driven to extinction by human activities,” says lead author Dr. Felix Grewe, co-director of the Field Museum of Natural History’s Grainger Bioinformatics Center, in a media release.

“There was a long standing question as to whether the Xerces blue butterfly was truly a distinct species or just a population of a very widespread species called the silvery blue that’s found across the entire west coast of North America.”

“The widespread silvery blue species has a lot of the same traits,” adds Professor Corrie Moreau, director of the Cornell University Insect Collections. “But we have multiple specimens in the Field Museum’s collections, and we have the Pritzker DNA lab and the Grainger Bioinformatics Center that has the capacity to sequence and analyze lots of DNA, so we decided to see if we could finally solve this question.”

Century-old DNA still paints a clear picture

To see if the Xerces blue really was its own separate species, Prof. Moreau and her colleagues turned to pinned butterfly specimens stored in drawers in the Field’s insect collections. Using forceps, she pinched off a tiny piece of the abdomen of a butterfly, collected in 1928.

“It was nerve-wracking, because you want to protect as much of it as you can,” Moreau says. “Taking the first steps and pulling off part of the abdomen was very stressful, but it was also kind of exhilarating to know that we might be able to address a question that has been unanswered for almost 100 years that can’t be answered any other way.”

Once researchers retrieved the piece of the butterfly’s body, the sample went to the Field Museum’s Pritzker DNA Lab where the tissues were treated with chemicals to isolate the remaining DNA.

“DNA is a very stable molecule, it can last a long time after the cells it’s stored in have died,” Dr. Grewe explains.

Even though DNA is a stable molecule, it still degrades over time. However, there’s DNA in every cell, and by comparing multiple threads of DNA code, scientists can piece together what the original version looked like.

“It’s like if you made a bunch of identical structures out of Legos, and then dropped them,” Prof. Moreau continues. “The individual structures would be broken, but if you looked at all of them together, you could figure out the shape of the original structure.”

Could the Xerces blue make a comeback in the future?

The team compared the genetic sequence of the Xerces blue butterfly with the DNA of the more widespread silvery blue butterfly. They discovered that the Xerces blue’s DNA was different, meaning it’s a separate species.

“The Xerces blue butterfly is the most iconic insect for conservation because it’s the first insect in North America we know of that humans drove to extinction,” Moreau reports. “There’s an insect conservation society named after it. It’s really terrible that we drove something to extinction, but at the same time what we’re saying is, okay, everything we thought does in fact align with the DNA evidence.”

“If we’d found that the Xerces blue wasn’t really an extinct species, it could potentially undermine conservation efforts,” the Cornell researcher says.

Although the Xerces blue is no more, the research team does note the possibility of reviving the extinct species using a “Jurassic Park”-style approach.

“Before we start putting a lot of effort into resurrection, let’s put that effort into protecting what’s there and learn from our past mistakes,” Dr. Grewe cautions.

“We’re in the middle of what’s being called the insect apocalypse — massive insect declines are being detected all over the world,” Prof. Moreau adds. “And while not all insects are as charismatic as the Xerces blue butterfly, they have huge implications for how ecosystems function.”

“Many insects are really at the base of what keeps many of these ecosystems healthy. They aerate the soil, which allows the plants to grow, and which then feeds the herbivores, which then feed the carnivores,” Moreau says. “Every loss of an insect has a massive ripple effect across ecosystems.”

“When this butterfly was collected 93 years ago, nobody was thinking about sequencing its DNA,” Dr. Grewe concludes. “That’s why we have to keep collecting, for researchers 100 years in the future.”

SWNS writer Stephen Beech contributed to this report.