The last of the Xerces blue butterflies fluttered in the air in San Francisco in the early 1940s. Now, it can be seen only in glass exhibits in museums.
These pearl-winged insects lived in coastal sand dunes along San Francisco and were first identified by scientists in 1852. When urban development swept through this part of California, the sandy soil was disturbed. This caused a ripple effect, eliminating the types of caterpillar plants that used them. The habitat change was too great for the Xerces blue butterfly, and the species became extinct.
«The blue Zerses moth was the first insect in the United States documented to be extinct by human activities,» said Cory Morrow, director of the Cornell University Insect Group, and Martha N and John C. and Cornell Biodiversity, and author of a new study on the Xersis butterfly.
«Habitat transformation and urban development have caused the loss of this species. The Xerces blue butterfly has become a symbol of insect conservation. In fact, the largest insect conservation organization is named even after this species.»
But scientists have long wondered whether Xerces is a distinct species, if it’s a subspecies or really just an isolated group of another species of butterfly, the silvery blue that lives across the western United States and Canada.
Morrow, who started working on this as a researcher at the Field Museum in Chicago, and her colleagues began turning to museum scholars to answer the question.
The new study was published Tuesday in the journal Biology Letters.
«Museum science is museum collections’ use of genome sequencing and other analytical techniques that were unimaginable even when the majority of museum samples were collected,» Morrow said. «What makes this so unprecedented is that we can address questions that cannot be answered any other way. This study is a great example of that because we can’t go out and collect the blue butterfly Xerces and the only way to address genetic questions about this species is to turn to museum collections.»
The Field Museum is home to multiple specimens of the Xersis blue butterfly, so Morrow and her colleagues decided to extract DNA from a 93-year-old butterfly specimen in the museum’s collection and see if it met the conditions for belonging to a unique species.
How do you extract DNA from a proven butterfly that is nearly a century old? Use extreme caution with tweezers. Moreau was able to recover the DNA after pressing on a small part of the insect’s abdomen.
“It was nerve-wracking, because you want to protect as much of it as possible,” Moreau said. “Taking the first steps and a flat stomach was very stressful, but it was also exhilarating to know that we might be able to answer a question that has not been answered for nearly 100 years and cannot be answered by any other way.”
The field museum also includes the Grainger Center for Bioinformatics, which has the ability to sequence and analyze DNA.
«DNA is a very stable molecule, and it can persist long after the death of cells stored in it,» Felix Grewe, lead study author and director of the Grainger Center for Bioinformatics, said in a statement.
The study team was able to retrieve enough strands of DNA to compare it to the DNA of the silver blue butterfly and determine that the Xerces blue butterfly was a separate species — and humans had already caused its extinction.
«It’s interesting to reiterate that what people have been thinking for nearly 100 years is true, and that this species was a species driven by human extinction,» Grewe said. «When this butterfly was collected 93 years ago, no one would have thought to sequence its DNA. That’s why we have to keep collecting, for researchers 100 years in the future.»
Next, the researchers want to understand whether these species, once considered genetically diverse, have experienced a decline in diversity as they neared extinction. That could be a contributing factor to its early end.
The researchers said the team was able to retrieve enough genetic information to prove that Xerces was a unique species, but not enough to revive the butterflies. There are many factors to consider before attempting to bring the species back through extinction.
«Although I know there are some people who are interested in reviving these species, I think we have a long way to go before we can actually do that,» Morrow said. “It will take significant time and financial resources to not only recap its genome, but also create the host plants required for larvae and native symbiotic ants. During this time of global insect decline, I would prefer to see our resources dedicated to saving those species that are already endangered or protecting critical habitats. «.
Meanwhile, other butterflies are experiencing a decline, such as El Segundo Blue, due to the loss of dune habitat, and Karner Blue due to the loss of the blue lupine flower used by caterpillars, according to Morrow.
“Before we begin to put so much effort into the resurrection, let us make that effort to protect what is there and learn from our past mistakes,” Grewe said.
The researchers note that we are in the middle of what many scientists are calling the insect apocalypse as species are in decline around the world — something to which humans have contributed significantly.
«The current apocalypse for insects is really a thousand cuts of death,» Moreau said. “Pesticide use, land use modification and climate change are probably the main factors causing this global decline in insects and all of these factors are caused by human activities. I think it is in our interest to try to mitigate as many of these factors as possible since all species on the planet matter” .
The researchers said insects are more important to our lives than most people realize. Although it may not be as pretty or attractive as the Xerces blue butterfly, it does aerate the soil and aid in plant growth, which nourishes everything else.
«Since insects are essential to any ecosystem, the loss of any species has multiplier effects in society,» Morrow said.
“As we can see from these examples above, the interdependence of species from mutualists to food plants and habitat requirements can have huge impacts on species survival. And to be honest without insects, our planet would become inhospitable to humans within months. We need to Insects even if we don’t always realize it.»