Thirty-one years ago, a scientist from Ontario named Laurence Packer described the disappearance of the Karner blue butterfly from a location in his Canadian province. Over the span of four hot, dry years, this local population went from “large and healthy” to nonexistent.

Writing about the disappearance in 1994, Packer made a prescient observation about the relatively new field of climate change science.

“[E]ven moderate sized populations may not be safe, especially when weather conditions are unusual,” he wrote. “This point about weather conditions may be particularly important, considering the climatic changes that many expect from global warming.”

Three decades later, Packer’s prediction has held true. Karner blues (Lycaeides melissa samuelis) have continued to dwindle and disappear, with more populations wiped out as climate change, along with habitat loss, pesticides, and other forces, have severely interrupted the creature’s sensitive life cycles. Its population has plummeted and it is today only found in a few areas, clinging to existence in isolated locations from northwest Wisconsin to New York, and local populations continue to occasionally abruptly die out.

Wisconsin has the largest population of Karner blues in the country. One of the state’s refuges is the region near the St. Croix River in Burnett County, particularly Crex Meadows and Fish Lake Wildlife Areas. Wildlife scientists and managers keep a careful eye on the butterflies.

Troubling trends

The Wisconsin Department of Natural Resources recently reported on the results of annual surveys for Karer blues across its range in the state last year. The work is part of protecting the remaining population by restoring habitat and other methods. The DNR reported a significant decline across its survey sites.

“The number of butterflies per acre in 2024 was the lowest when compared to all 17 survey years,” reported Chelsea Weinzinger, the agency’s Karner blue recovery coordinator.

Then, this week, a team of researchers published a peer-reviewed article in the journal Science that showed butterflies across the United States in serious decline over the past two decades. Analyzing several studies, including citizen science projects that gathered data from volunteer observers, the scientists found about a fifth fewer butterflies now than at the turn of the century.

“Between 2000 and 2020, total butterfly abundance fell by 22% across the 554 recorded species,” the scientists wrote. “Species-level declines were widespread, with 13 times as many species declining as increasing.”

The study analyzed the records of 12 million butterflies from nearly 77,000 surveys, and found the populations of nearly all the 342 species with significant data had shrunk. “[T]he team found only nine species—just 3%—that had increased in number,” they wrote.

Complex causes

Butterfly populations can rise and fall rapidly due to a variety of factors. Some of the same factors that can make them sensitive to change also mean they can bounce back quickly.

“Because they have such short generation times, even small conservation steps can make a big difference and we can see populations bounce back,” wrote Dr. Eliza Grames, one of the researchers on the national study, in a separate article this week.

The biologist even singled out the Karner blue as a cautious cause for optimism.

“With restoration efforts, one Karner blue population in the Albany Pine Bush Preserve in New York rebounded from a few hundred individuals in the early 1990s to thousands of butterflies,” Grames wrote.

But the butterfly’s future is still fragile. While restoration brings back habitat and butterflies in some places, they blink out of existence at other sites. The populations are disconnected, based on a careful balance of local conditions.

Ups and downs

Karner blues usually have two broods each year. Eggs that overwintered from the previous summer become caterpillars in the spring, feeding exclusively on wild lupine, and then become adults in mid-May to mid-June. As adults, they live only about five days, just long enough to reproduce. Females lay eggs on or near wild lupine plants, and then a second brood is born in July to August. When they metamorphose into adults, they lay the eggs that will become the next generation the following spring.

The Wisconsin DNR points to the weather the past two years as possibly having caused a short-term Karner blue decline that could still be reversed.

“A likely contributing factor to the reduced population estimates is the summer drought in 2023 (5th driest on record) followed by an extremely wet 2024,” Weinzinger wrote. “The summer of 2024 ranked as the 6th wettest summer on record for Wisconsin. And the spring was exceptionally wet ranking as the 4th wettest spring on record. Anecdotally, heavy spring/early summer rain benefited lupine but may have negatively impacted Karner 1st flight emergence.”

The 2024 report shows the population reduction in straightforward numbers. Agency scientists counted Karner blues on 305 acres across seven sites in seven counties in 2024. They came up with an estimate of a total population of 8,861 butterflies on those 305 acres. Meanwhile, observers including volunteers visited another 95 sites last year, just determining if any Karner blues were present. They found the butterflies at 60 of those sites. That led to a calculation of the number of butterflies per acre at its lowest number since surveys began 17 years ago.

But, the scientists also said the species was continuing to colonize new habitat faster than it was disappearing from other locations.

Losing lupine

Weather isn’t the only worry for Karner blues. For another thing, they are totally dependent on one plant species: wild lupine, and the specific habitat where it’s found. The butterfly’s caterpillars will only feed on lupine before metamorphosing into adults, and only along the northern edge of lupine’s range. This is primarily open sand barrens with sparse oak and pine trees.

Adult Karner blues love sunshine, but their caterpillars get more nutrition from lupine that grows in partial shade. The adult insect’s large surface area means it easily dries out during drought. Like many butterfly species, Karner blue caterpillars secrete a sweet substance that ants love; the ants in turn protect the caterpillars from predators.

It’s a food web of the finest thread. The complex connections and cycles makes it sensitive to a variety of changes. Despite being listed as endangered in 1992, and despite extensive habitat restoration and other protection efforts since completion of an action plan in 2003, Karner blues continue to struggle.

“The [Karner blue] should continue to remain listed as endangered because, since the species was listed, it has been extirpated from recovery units in Minnesota and Indiana,” the U.S. Fish and Wildlife Service in its last assessment of the species in 2019. “Additionally, although some populations have demonstrated some improvement, others have remained low or are demonstrating a decline. In addition, the KBB has been found to be highly sensitive to both direct and indirect climate change impacts. Other threats present at the time of listing, such as loss of habitat due to natural succession, lack of management, invasive species and commercial, industrial and residential development, also continue to persist for the species.”

Shrinking range

Minnesota is truly at the western range of the Karner blue butterfly, as it is also the extremity of where wild lupine grows. Today, there is only one known Karner blue population in the state, at the Whitewater Wildlife Management Area in southeastern Minnesota. Until the early 1980s, there was another population at the University of Minnesota’s Cedar Creek Natural Heritage Area in Anoka County, on the edge of the St. Croix River watershed. Then a road was built through the stand of wild lupine where they were found, and the butterflies disappeared.

The type of landscape Karner blues require has been nearly erased from existence over the past couple centuries. Open land will generally grow over in trees without regular fire or other disturbances, habitat can be plowed up for agriculture, and climate change’s impact on temperatures, seasonal timing, and precipitation patterns can quickly disrupt Karner blue survival.

Another population of Karner blues was wiped out in 2014, the southernmost known population, found on sand dunes at the tip of Lake Michigan in Indiana. Over the course of a few very hot and dry years, the population completely disappeared. Scientists saw the event as a case study in climate change impacts on endangered species, describing them as “blue snowflakes in a warming world.” Meanwhile, the next most southern population, in Ohio, has dropped to dangerously low numbers.

“The prevalence of declines throughout all regions in the United States highlights an urgent need to protect butterflies from further losses,” the scientists wrote.

Conservation potential

Karner blue populations can bounce back nearly as quickly as they fall when habitat is restored and other conditions are met. Activities such as prescribed burns to keep sandy grasslands open can promote the growth of lupine, other flower species that adults feed on, and the overall type of habitat the butterflies prefer.

In the St. Croix River region, Karner blue habitat stretches up the east side of the river from the Sterling Barrens to south of the Namekagon River. It is found at Crex Meadows and Fish Lake Wildlife Areas, as well as Governor Knowles State Forest and Burnett and Polk County Forest. Land management agencies are involved in efforts to protect and expand habitat for the butterflies on their properties.

In 2019, the Wisconsin DNR acquired another 321 acres of prime Karner blue habitat that it added to Crex Meadows. The U.S. Fish and Wildlife Services contributed the federal funds needed to make the habitat protection possible.

The Karner blue is closely related to several cousin butterflies. It took a writer to notice their uniqueness. The species was first described for science by the novelist Vladimir Nabokov. He later described the butterflies for literature, without naming them, in his 1957 novel, Pnin.

“A score of small butterflies, all of one kind, were settled on a damp patch of sand, their wings erect and closed, showing their pale undersides with dark dots and tiny orange-rimmed peacock spots along the hindwing margins; one of Pnin’s shed rubbers disturbed some of them and, revealing the celestial hue of their upper surface, they fluttered around like blue snowflakes before settling again.”

References and more information

Edwards, Collin B., et al. “Rapid Butterfly Declines across the United States during the 21st Century.” Science, vol. 387, no. 6738, Mar. 2025, pp. 1090–94. science.org (Atypon), https://doi.org/10.1126/science.adp4671.

Weinzinger, Chelsea. 2024 Karner Blue Butterfly Summer Survey Results. Wisconsin Department of Natural Resources, 2025.

Andow, David A., et al. Karner Blue Butterfly: A Symbol of a Vanishing Landscape. 1994. conservancy.umn.edu, https://hdl.handle.net/11299/192310.

Bergquist, Lee. “DNR Adding Land Holdings to Aid Endangered Karner Blue Butterfly.” Milwaukee Journal Sentinel, 27 Feb. 2019, https://www.jsonline.com/story/news/local/wisconsin/2019/02/27/dnr-adding-land-holdings-aid-endangered-karner-blue-buterfly/2996305002/.

Li, Yudi. Assessment of the Karner Blue Butterfly’S Response and Managed Relocation Under Climate Change. 2020. University of Minnesota. conservancy.umn.edu, https://hdl.handle.net/11299/216072.

Marsh, Dawn. “Recovering the Karner Blue Butterfly.” U.S. Fish & Wildlife Service, Fish & Wildlife News, 7 Sept. 2023, https://www.fws.gov/story/2023-09/recovering-karner-blue-butterfly.

Schuurman, Gregor, et al. Blue Snowflakes in a Warming World: Karner Blue Butterfly Climate Change Vulnerability Synthesis and Best Practices for Adaptation. National Park Service, 2023. DOI.org (Crossref), https://doi.org/10.36967/2301333.