Monarch Butterflies Are Vanishing — Here Is What Scientists Are Doing About It

Every autumn, one of nature’s most spectacular events unfolds along the California coast. Millions of monarch butterflies complete an epic migration, a long seasonal journey to a warmer location, arriving at groves of eucalyptus and cypress trees to cluster together through the winter months. Volunteers and scientists gather to count them carefully, hoping to see numbers climb. But recently, the counts have told a worrying story, and a major scientific study has confirmed what many conservationists feared: butterflies across North America are disappearing at an alarming rate.

Natalie Johnston is the interpretive programs manager at the Pacific Grove Museum of Natural History in California, which means she helps explain the natural world to visitors and coordinates conservation efforts at the nearby Pacific Grove Monarch Sanctuary. Every week, she and a team of volunteers scan the sanctuary’s two acres with binoculars, carefully sorting what they observe into categories like “sunners” warming their wings in the morning light and “loners” resting on their own. In January 2024, however, Johnston made a devastating discovery: around 200 monarchs were dead or dying on the ground near the sanctuary, their bodies piled together and their abdomens curled in distress. A toxicology report, which is a scientific analysis of what chemicals are found in an organism’s body, later revealed a mixture of pesticides in the dead butterflies, including chemicals typically found in products people spray in their gardens and yards.

That mass die-off was a dramatic and visible example of a problem that plays out invisibly across the entire continent. In March 2025, scientists published a landmark study in the journal Science alongside a State of the Butterflies report from the Xerces Society for Invertebrate Conservation, an organization focused on protecting insects and other spineless animals. The research covered 554 butterfly species and found that overall butterfly populations across the United States declined by 22 percent between 2000 and 2020. That is roughly one in every five butterflies gone in just twenty years. Twenty-four species declined by 90 percent or more during that same period, including the tailed orange of the dry southwest, the West Virginia white of the Appalachian forests, and the ruddy copper of the western mountain ranges. Western monarch butterflies face an especially grim outlook, with scientists estimating a 99 percent chance of the population vanishing entirely by 2080 without serious intervention.

What is driving this collapse? Scientists point to three overlapping forces: pesticide use, habitat loss, and climate change. Scott Black, the executive director of the Xerces Society and one of the study’s co-authors, explained that visible threats like bulldozed land, floods, or drought are easier for people to recognize and respond to. Pesticides, though, are essentially invisible. After World War II, chemical companies developed powerful insecticides, chemicals engineered specifically to kill insects, to combat the pest problems created by monoculture farming, which means growing only a single crop across large areas of land. Over the following decades, formulas evolved to become even more targeted and more potent. Today, according to Black, the insecticides being used are more toxic than older versions, more varieties are being applied at once, and they are being sprayed across far larger landscapes than ever before. A study published in the journal Environmental Toxicology and Chemistry found that of 336 plants sampled at urban sites in New Mexico and California, including milkweed plants that monarch butterflies depend on for survival, only 22 had no detectable pesticide levels at all. The rest had been contaminated, often without anyone intending to harm butterflies at all.

Despite the unsettling numbers, there are meaningful reasons for hope. Hundreds of scientists, conservationists, and everyday volunteers are now working together to monitor butterfly populations, restore habitat, and press for changes in how and where pesticides are used. The eastern monarch population, which winters in the oyamel fir forests of central Mexico rather than along the California coast, saw its overwintering habitat increase by 64 percent in 2026 compared to the previous year, a significant sign that conservation efforts can produce real results. Milkweed restoration projects are expanding, and sanctuaries like the one in Pacific Grove draw both researchers and community members into active roles in protecting these insects. What scientists have learned is that protecting monarch butterflies tends to benefit hundreds of other species at the same time, because the conditions monarchs need, including clean plants, open habitats, and reduced pesticide exposure, are the conditions most butterflies and many other insects need as well. Monarchs, in that sense, act as a signal species, meaning their health reflects the health of entire ecosystems.

Source: Smithsonian Magazine