Western Monarch Butterfly Faces Critical Decline: Scientists Race to Prevent Species Extinction

Western Monarch Butterfly Faces Critical Decline: Scientists Race to Prevent Species Extinction

New research reveals that western monarch populations have a 99 percent chance of vanishing by 2080, prompting conservationists to implement tracking technology and habitat restoration efforts to save the iconic species from disappearing.

A Quiet Sanctuary Under Threat

On a misty November morning at the Pacific Grove Monarch Sanctuary near California's coast, interpretive programs manager Natalie Johnston and a team of volunteers conduct their weekly census of the monarch butterflies that cluster in eucalyptus and Monterey cypress trees. The sanctuary, nestled among residential homes, typically provides refuge for millions of monarchs undertaking one of nature's most extraordinary migrations—yet the numbers have become alarmingly sparse.

Every year, monarch butterflies flutter across North America toward warmer climates. While eastern populations migrate to Mexico's oyamel fir forests, western monarchs travel instead to coastal California sanctuaries like Pacific Grove. These delicate insects depend on the sun's warmth to fly, making cool mornings ideal for counting. During a recent count, volunteers documented only 99 monarchs scattered throughout the grove.

A Catastrophic Discovery

Johnston's experience took a devastating turn in early 2024 when she discovered approximately 200 dead or dying monarchs on private property adjacent to the sanctuary. "For so many of them to be wiped out in a single event in a place that was supposed to be safe was just horrible," Johnston recalled. Over the subsequent two weeks, staff and volunteers continued observing monarchs displaying identical symptoms—spasming abdomens and paralysis.

A toxicology report released a year later revealed the culprit: a combination of pesticides contaminated the dead insects' bodies, including compounds commonly found in residential pest control sprays. This mass casualty event exemplifies a broader ecological crisis affecting butterfly populations across the United States.

An Unprecedented Butterfly Decline

For the first time, scientists have documented the full scope of butterfly population collapse in a March 2025 study published in the journal Science and a corresponding State of the Butterflies report from the Xerces Society for Invertebrate Conservation. The analysis examined 554 butterfly species and estimated trends for 342 of them, finding that between 2000 and 2020, butterfly populations declined overall by 22 percent across the country.

The statistics are sobering: 24 butterfly species declined by 90 percent or more during this two-decade period. Species like the tailed orange, West Virginia white, and ruddy copper have suffered particularly steep losses. Most critically, the U.S. Fish and Wildlife Service projects that eastern monarch populations face a 56 to 74 percent chance of extinction by 2080—while western monarchs face a 99 percent probability of vanishing within the same timeframe.

"When a bulldozer comes through, or a giant flood from climate change happens, or a drought happens, or even an invasive species moves in—that's something you can see," explains Scott Black, executive director of the Xerces Society and co-author of the Science study. "But pesticides are essentially invisible. They're an unseen, massive threat."

The Invisible Menace of Modern Pesticides

Although pesticide use dates back millennia—ancient Sumerians in Mesopotamia applied sulfur dusting around 2500 B.C.E.—modern chemical formulations pose unprecedented threats to insect populations. Following World War II, chemical companies in the United States developed powerful synthetic insecticides like DDT to combat pest populations that thrived in monoculture farming systems.

Public outcry against DDT in the 1960s led pesticide manufacturers to create new formulas intended to cause less harm to humans while proving orders of magnitude more lethal to insects. Black characterizes the industry mindset as "spray first and ask questions later." The result: "The insecticides we're spraying are more toxic. We're spraying different kinds that are combining, and we're spraying more of these chemicals across these landscapes."

Research by University of Nevada Reno ecologist Matt Forister reveals the extent of contamination. In a September study published in Environmental Toxicology and Chemistry, Forister's team analyzed 336 individual plants, including milkweeds essential to monarch survival, at urban sites in Albuquerque, New Mexico, and Sacramento, California. Only 22 plants contained no detectable pesticide residues. On average, plants harbored at least three distinct chemical types, with 71 containing pesticide concentrations lethal or nearly lethal for butterflies.

Earlier investigations proved equally alarming. A 2022 study examined 235 milkweed plants from 33 retail nurseries across the United States, detecting 61 different pesticides with an average of 12.2 pesticides per plant. A 2020 analysis of milkweed across California's Central Valley and retail plant stores identified 64 distinct insecticides, herbicides, and fungicides across all 227 samples tested.

"We couldn't find a milkweed leaf in the north Central Valley that didn't have pesticides in it or on it," Forister notes. "Of this very long list, only a small number have ever been tested on a monarch caterpillar—and that's just the monarch. When you think about the more than 150 other butterflies in the state, we know almost nothing."

Multiple Threats Converging

Black describes the butterfly's predicament as a "death by a thousand cuts" scenario. While pesticides decimate insect populations, habitat destruction and intensifying droughts driven by climate change compound the crisis. Despite these formidable challenges, Forister maintains that even modest interventions could generate significant improvements. Critically, while addressing habitat loss and climate change requires sustained effort, pesticide use could theoretically be curtailed much more rapidly.

"Insects are just amazing at responding very quickly to anything good that people do," Forister observes. "If people stop putting insecticides in their yards, they'll see more insects. Even in the heart of the Central Valley, we continue to be surprised by the level of resilience."

Learning from Success Stories

About 60 minutes south of Pacific Grove lies Lighthouse Field State Beach in Santa Cruz, where another concentration of overwintering monarchs congregates among protective Monterey cypress trees. Here, hundreds of orange-winged monarchs flutter between branches on warm November afternoons—a breathtaking display that draws crowds of awestruck visitors.

The current numbers tell a grim story. While 2021 witnessed thousands of butterflies at Lighthouse Field and hundreds of thousands across nearly 300 overwintering sites, the 2025-26 season recorded near-record lows, with only 12,260 total monarchs across 249 sites—marking the third-lowest count since monitoring began in 1997.

Yet hope exists. Cheryl Schultz, an ecologist at Washington State University Vancouver and senior author of the Science paper, led the successful recovery of another endangered butterfly species: the Fender's blue. First documented in Oregon's Willamette Valley during the 1920s, this small butterfly disappeared in the 1930s due to destruction of its host plant, Kincaid's lupine. Scientists rediscovered a remnant population near Eugene, Oregon, in the late 1980s.

Schultz spearheaded extensive habitat restoration efforts, establishing approximately 90 sites with restored lupine populations across the Willamette Valley's upland prairies. Through dedicated fieldwork and community commitment spanning decades, the Fender's blue achieved a conservation victory: it became the first butterfly downlisted from "endangered" to "threatened" status under the Endangered Species Act.

"That little butterfly took a few decades, and it took a lot of people and a lot of commitment, but it can happen," Schultz says. "I have to hold on to that."

Advanced Technology Aids Conservation

While the Fender's blue success demonstrates that recovery is possible, monarch butterflies present unique challenges due to their migratory nature. To better understand the stresses on migratory species, researchers at Lighthouse Field are deploying ultralight radio tags weighing less than one-tenth of a gram. When attached to butterflies, these tags transmit Bluetooth signals to location-enabled mobile devices of nearby users, with data recorded in an app called Project Monarch.

This technology will enable scientists to track where female monarchs travel after leaving overwintering sites and identify optimal locations for habitat restoration. Conservationists could then apply the proven methods that saved the Fender's blue—prioritizing these sites and establishing milkweed habitat for future caterpillars.

Volunteer Diana Magor is simultaneously researching how heartleaf milkweed could bolster climate resilience in restored habitats. This variety blooms earlier than common or showy milkweed, a crucial advantage as climate change pushes seasonal timing earlier. When monarchs migrate before traditional milkweed species have sprouted, heartleaf milkweed could provide essential sustenance.

Multiple Pathways to Recovery

"When we restore these habitats and manage pesticides, we see change—positive change," Black emphasizes. "The diversity and abundance of insects goes up, and that happens really quickly."

A comprehensive recovery strategy requires action across multiple fronts: farms reducing pesticide applications, smarter land-use practices protecting wild spaces, and aggressive carbon emission reductions to forestall worst-case climate scenarios. However, despite intensive conservation efforts, numerous butterfly species will likely be lost.

Forister has taken an unconventional approach to this reality by founding a scientific journal documenting species extinctions. "It makes me feel better, because we're at least preserving a memory of things as they're going away and highlighting rare species that we can still look for," he explains.

Cautious Hope for the Future

At Natural Bridges State Beach, just miles north of Lighthouse Field, hundreds of monarchs navigate the canopy high above visitor boardwalks, moving with the grace of gently falling leaves. Yet the contrast is stark: decades ago, at least 120,000 monarchs overwintered at this location. In 2025, the count reached only 2,500 at its peak.

Despite overwhelming obstacles, these delicate insects complete their metamorphosis from caterpillars to butterflies each year—a transformation that has come to symbolize resilience for conservationists worldwide. For Johnston, Black, Forister, Magor, Schultz, and hundreds of others dedicating their efforts to protecting vulnerable populations, sighting the monarchs in flight provides motivation.

"There are a lot of people waking up and trying to do this," Black reflects. "Will it be enough at the end of the day? I don't know yet. But I go out and I look at these places and meet the people doing this great work, and it keeps me motivated."

Quick Fact: While western monarch counts have revealed concerning lows, the eastern monarch population showed improvement in 2026, with overwintering habitat increasing by 64 percent compared to the previous year.