Michelle So, Contributing Photographer

When folded in rest, the Mission blue butterfly’s wings are grey and dotted with black — no more special than a common house moth’s. Unfolded, this furry insect’s wings are iridescent and azure, delicately laced with a white border and otherworldly sheen.

The Mission blue butterfly lives exclusively around the San Bruno Mountain in California. There are an estimated 18,000 adults remaining in their original region. While its bright blues may seem better fitted for the tropics, mountainous regions are, in fact, hosts to two-thirds of butterfly species across the world, according to researchers. 

Recently, Yale researchers published a first-of-its-kind study in Nature Ecology & Evolution, using previously collected data to map out butterfly hotspots. 

“Unfortunately, our first global assessment of butterfly diversity and threats finds that butterflies’ fascinating diversification into higher-elevation environments might now spell their demise, with potentially thousands of species committed to extinction from global warming this century,” Walter Jetz, director of the Yale Center for Biodiversity and Global Change who oversaw the study, told the News. 

Today, climate change threatens the careful balance of the alpine regions, leaving the Mission blue and other fragile butterfly populations in considerable danger.

Climate Threat to Butterflies

Historically, conservation efforts have largely excluded butterflies and other insects to prioritize protecting land vertebrates, such as mammals or reptiles. Now, global assessments of insect biodiversity and climate change vulnerability have been lacking — primarily due to the limited and incomplete distribution data for most insect taxa.

Larry Gall, senior collections manager of the center’s entomology division and moth researcher, considers butterflies to be “specialized moths” that are active in the daytime as opposed to nighttime.

“As is true for most insects, Lepidoptera [the scientific name for butterflies and moths] in their various life stages are involved in pollination, nutrient cycling and other important roles in ecosystems,” Gall wrote to the News. “[With] no habitat for Lepidoptera, [there would be] no springtime as we presently know it, and related tragedies.”

Gall’s alarming message regarding the butterfly threat is not unfounded. However, not much has been done in part due to the lack of information available.

According to Jetz, ignoring insect populations in conservation sciences has created “vast global knowledge gaps,” potentially leading to past conservation decisions that were uninformed.

“Our study is the first to systematically identify and assess butterfly biodiversity hotspots, establishing a clear and strong connection with mountain regions which harbour a disproportionately high percentage of butterfly diversity,” Jetz wrote.

The researchers pored through atlases, field guides and the extensive pre-existing literature on butterflies. They then used automated models that integrated these official records with citizen-scientist data.

In the publication, the team used colorful legends to depict higher concentrations of species of butterflies at higher altitudes.

The main findings? Mountains are critical for butterfly biodiversity. 

Mountain, or alpine, ecosystems are unique due to their physical structures. In addition to being large physical barriers, mountains also serve as environmental buffers. Precipitation levels, temperature and environmental conditions are all more stable in these areas.

However, as outlined in a 2022 article published in PeerJ, mountain environments today are in a “state of rapid transition as a consequence of climate change in the Anthropocene.”

The overall increase in temperature may cause ice cover — a useful sort of “sunshade” — to melt, exposing dark rock that absorbs rather than reflects heat. As the ice melts more, the speed of water run-off that reaches lower-lying ecosystems may increase, changing the way ecosystems or even cities deal with the influx of ice melt.

Regionally, changes in weather patterns may reduce the number of frost days, alter the treeline of forested regions and change the way plants interact with their environment— all of which will indirectly affect butterfly populations. 

“Our results suggest that mountain areas — once vital refugia — are increasingly at risk of becoming biodiversity traps,” Stefan Pinkert, a University of Marburg lecturer and former postdoc in Jetz’s lab, said. 

Pinkert is also the lead author of the study. 

Even then, the data is incomplete. The results are “broad, yet conservative,” according to Pinkert, and don’t offer a complete image of the butterflies’ interactions with other organisms.

Looking Ahead

Protecting these delicate insects extends far beyond just saving their kind.

Butterflies are a vital component of Earth’s biodiversity. As caterpillars, they are often specialized herbivores that help regulate plant abundance and contribute to nutrient cycling; as adults, they pollinate flowering plants. 

This evolutionary relationship they have with plants makes both groups not only ecologically important but also “highly vulnerable.” A loss in butterflies and pollinators as a whole will deeply impact humans — economically and emotionally.

“Just as plants may face greater extinction risks from the loss of associated butterflies, their decline would, in turn, accelerate the precarious situation butterfly populations are facing,” Pinkert said. “While the knowledgebase for other insect groups is even more limited, conservation priorities for butterflies and their vulnerability likely apply to many terrestrial insects. This suggests unfortunately very dire consequences for biodiversity and ecosystem functioning in the coming decades, urging rapid and targeted conservation and restoration efforts.”

With newfound information on butterfly hotspots, Pinkert suggests that governments can increase protections by expanding protected natural areas into mountains, where environmental pressures from human land-and-resource use are increasing.

Governments can also “implement migration corridors and targeted conservation of hotspots of butterfly rarity,” Jetz said.

However, last month, the Trump administration implemented aggressive “rollbacks” on regulations issued by the Environmental Protection Agency, the federal entity responsible for protecting natural lands.

Those who care about butterflies can still do their part in protecting them. 

Butterflies don’t need much space, Pinkert says. Local landowners can set aside small plots of land of butterfly-friendly habitats to support stable populations. 

“Simple measures—such as managing meadows extensively without the use of fertilizers or pesticides—can make a significant difference,” Pinkert wrote. “Many species will readily return to gardens, field margins, and other semi-natural areas if the right conditions are restored.”

Even citizens, unfamiliar with the thousands of species of butterflies, may be able to boost conservation, Pinkert says. By utilizing the iNaturalist app, users can contribute images of species they might happen upon in their neighborhood or vacations abroad.”

The Yale Peabody Museum houses over 350,000 butterfly and moth specimens.