Where did all the monarch butterflies go?
After decades of decline, the invertebrate could soon receive protection under the Endangered Species Act.

Once a common sight in gardens and fields, western monarch-butterfly populations have plummeted more than 90% since the 1980s.
The U.S. Fish and Wildlife service has finally taken action, announcing in December a proposal that monarchs be listed as a threatened species under the Environmental Protections Act by the end of 2025. The proposal comes at a pivotal moment, as organizations such as the National Wildlife Federation and Monarch Watch push for protective measures that could reverse the species’ decline.
Robert Hancock, Ph.D., a professor of Biology at Metropolitan State University of Denver, first noticed the decline of monarch butterflies while studying milkweed plants in Colorado. “As a secondhand observer of the decline, I’ve noticed fewer monarchs feeding on milkweed than in past years,” he said, noting he has been studying milkweed since the 1980s.
Hancock explained that the monarch-butterfly crisis is the result of several factors. “Deforestation, urban sprawl and the widespread use of pesticides have destroyed their habitats,” he said, “while rising temperatures and climate change have introduced new challenges, such as limited food availability and fewer places to lay their eggs.”
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Hancock added that the monarch’s life cycle is closely linked to milkweed, which provides food and a place for them to lay eggs. “Without milkweed, adult monarchs live and mate, but their young cannot survive without shelter and food that milkweed provides, and their entire lifecycle is disrupted as fewer reach adulthood,” he said. “Milkweed populations are shrinking due to development and pesticide use, and with the plants blooming earlier because of rising temperatures, monarchs have fewer places to feed and thrive as they migrate.”

The monarch’s annual migration, a journey spanning thousands of miles and crossing over three countries, has captured the imagination of filmmakers and artists for decades. The migratory route, and loss of habitat along the way, is a big part of the problem, Hancock explained.
How to plant milkweedIn Colorado, choose Showy Milkweed or Common Milkweed. Plant seeds in late fall before the first frost. If planting in spring, cold-stratify the seeds by refrigerating them in moist paper towels or soil. Pick the sunniest spot in your garden or place them in pots near a building, away from water runoff. Milkweed prefers light, well-drained soil, with seeds planted a quarter-inch apart. Water seedlings for the first few days, then water only during dry spells. As a perennial, milkweed will return each year, and you can collect seeds to plant again. If you don’t live in the Colorado area, use milkweed-finder tools to locate native species to find local vendors.
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“With habitat loss, especially due to increased herbicide use on these plants and the milkweed blooming earlier and being dormant sooner due to rising temperatures, monarchs often find no food when they arrive during their winter migration,” he said. “That’s why conservation efforts, such as habitat restoration, are critical right now for these species and others that depend on the plant.”
Christy Carello, Ph.D., professor of Biology at MSU Denver, is hopeful that the potential listing will have an impact on monarch populations. “The Endangered Species Act warrants that a species-recovery plan is developed,” she said. “The listing would require federal funding to be used for their recovery and that critical habitats are protected.”
Hancock and Carello are cautiously optimistic that the proposed designation, which is currently open for public comment and has a deadline for a final decision by December 2025, could help reverse the monarchs’ decline, but they stressed the need for sustained awareness and active conservation. Simple actions such as planting milkweed and nectar-producing flowers and avoiding pesticides in home gardens and on farms could go a long way in giving monarchs a fighting chance.
As for the public’s role, Hancock urges continued vigilance. “Monarch butterflies aren’t a critical food source or predator,” he said, “so their extinction wouldn’t disrupt the environment significantly. However, they are a symbol of our environment’s health. Protecting them shows how well we can protect the environment.”