Butterflies are in decline across North America, a look at the Western Monarch

On a misty Friday morning in November, with dawn’s last warm hues clinging to the gloomy clouds above, the Pacific Grove Monarch Sanctuary is whisper quiet. Even the persistent roar of the ocean, only a few minutes’ walk from this small copse among single-family homes, is deadened by walls of eucalyptus and Monterey cypress. The tires of approaching cars crunch on a gravel road that slips between two buildings, each adorned with murals of the brilliant monarch butterfly.

In one of those cars is Natalie Johnston, the interpretive programs manager at the Pacific Grove Museum of Natural History. With a pair of binoculars and a clipboard in hand, Johnston, along with a small cadre of volunteers, is canvassing this two-acre sanctuary in search of monarchs.

Every year, the monarch butterfly makes one of the animal kingdom’s most wondrous migrations as millions flutter across the United States to warmer climates. In the east, their destination is the cozy comfort of central Mexico’s oyamel fir forests, but the much smaller western monarch population—mostly separated from its eastern counterparts by the Rocky Mountains—instead makes its way to Pacific Grove and hundreds of similar sites along the California coast.

Because monarchs require the sun’s warmth to fly, cool mornings like this one provide the perfect opportunity to count them before they begin stirring. Peering into the canopy, the volunteers categorize the insects by their behavior, counting “sunners,” “grounders,” “loners” and even a “flier” or two. On her clipboard, Johnston notes the individual trees containing butterflies. Today, a few “loners” are scattered throughout the grove, and only one small collection of 72 is nestled together. The day’s final count: 99.

In the past few years, Johnston has experienced some emotional highs during these weekly counts, as in 2021, when a single tree hosted thousands of monarchs among its broad branches. But nothing prepared her for what she witnessed one Friday morning in early 2024.

“‘Oh my God, there are so many grounders,’” Johnston remembers saying after spotting some 200 dead or dying monarchs on private property near the grove. “We started counting—one, two, three, four, five—but they’re in these dense piles … spasming, their abdomens curled. … 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 describes that day as one of the worst experiences of her life. Over the next two weeks, staff and volunteers continued to see dying monarchs with the same symptoms, though in smaller numbers. A toxicology report published a year later revealed a cocktail of pesticides in the dead insects’ bodies, including some toxins typically found in residential sprays.

This mass casualty is just one highly visible event among many invertebrate dramas that play out every day. Monarchs, as well as hundreds of other butterfly species across the U.S., are struggling to survive against toxic pesticides, habitat loss and a rapidly changing planet. Eastern monarchs face a 56 to 74 percent chance of extinction by 2080, according to the U.S. Fish and Wildlife Service. And western monarchs, during that same period, have a 99 percent chance of vanishing.

Quick fact: A spot of hope

While western monarch counts recently revealed low numbers, the eastern monarch population had some good news in 2026. The amount of habitat occupied by overwintering eastern monarchs increased by 64 percent compared with last year.

Since time immemorial, butterflies like the monarch have been an irreplaceable part of our wild world, but without our help, most of them may soon disappear. That’s why hundreds of scientists, conservationists and volunteers are working together to count and protect this species before it’s too late—because what’s good for the monarch is good for other butterflies as well.

The plight of the butterflies

The monarch is only one of the U.S.’s 750 or so butterfly species, each with its own incredible patterns and idiosyncrasies. The tailed orange, for example, flits about the dry southwest. The West Virginia white calls the moist deciduous forests of the Appalachians home. The natural range of the ruddy copper, with its shocking orange flair, stretches the width and breadth of the western mountain ranges. Although these three species differ in appearance, numbers and geography, they’re all in decline.

For the first time, scientists illustrated the full extent of this ecological crisis in a study published in the journal Science in March 2025 and in a subsequent State of the Butterflies report from the Xerces Society for Invertebrate Conservation. The report covered 554 species and estimated trends for 342 of them, as insufficient data was available for the others. From 2000 to 2020, researchers found, butterflies declined overall by 22 percent across the country. Although some butterflies saw modest increases during that time, a majority did not—and 24 species declined by 90 percent or more, including the tailed orange, the West Virginia white and the ruddy copper.

“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,” says Scott Black, executive director of the Xerces Society and co-author of the Science study. But pesticides, as demonstrated by the Pacific Grove casualties, are essentially invisible, he adds. “They’re an unseen, massive threat.”

Pesticides in some form or another have been around nearly as long as recorded history: Ancient Sumerians in Mesopotamia used sulfur dusting to control pests and mites around 2500 B.C.E. But after World War II, chemical companies in the U.S. created powerful insecticides like Dichlorodiphenyltrichloroethane, or DDT, to control growing pest populations spurred by the vulnerabilities inherent in raising only one crop, or monoculture farming.

Public backlash against DDT in the 1960s led to new pesticide formulas designed to cause less harm to other living things, including humans, while being orders of magnitude deadlier to insects—sort of like trading in an indiscriminate chemical shotgun for a hyper-focused sniper rifle. Across the pesticide industry, the prevailing mind-set, according to some conservationists, became “spray first and ask questions later”—or maybe don’t ask questions at all.

“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,” Black says. This is why “butterflies and other insects are declining at greater rates in the 2000s than in the past.”

In a study published in September in the journal Environmental Toxicology and Chemistry, the University of Nevada Reno ecologist Matt Forister and his team analyzed 336 individual plants, including milkweeds vital to the monarch’s survival, at urban sites in Albuquerque, New Mexico, and Sacramento, California. They found that only 22 of those plants had no detectable levels of pesticides. On average, the plants contained at least three types of chemicals, and 71 of them contained concentrations of pesticides that are lethal or nearly lethal for butterflies.

In a similar study in 2022, Forister and his team tested 235 milkweed plants from 33 retail nurseries across the U.S. and detected 61 different pesticides, with an average of 12.2 pesticides per plant. This echoes the findings of a 2020 study in which Forister tested milkweed plants across 19 sites in California’s Central Valley and two stores that sell plants to home gardeners—pesticides were found in all 227 samples.

“We couldn’t find a milkweed leaf in the north Central Valley that didn’t have pesticides in it or on it,” says Forister. The 2020 study counted 64 different insecticides, herbicides and fungicides in total. “Of this very long list, only a small number have ever been tested on a