Federal wildlife officials proposed on Tuesday that monarch butterflies receive protection as a threatened species.

The flashy orange and black butterflies, which flutter forth each year on an epic migration that spans thousands of miles and multiple generations, are found from coast to coast in the United States during warmer months. Despite precipitous declines, they are still prevalent enough that, if the proposal goes through, they would become the most commonly seen species to receive federal protection.

That means officials are walking a tightrope with the proposal. Restrict too few activities that harm monarchs, and officials risk creating a merely symbolic listing that does little to stave off further declines. Restrict too many, and they could trigger a political backlash.

Tight rules could also backfire by dissuading people from creating butterfly habitat on their property, because the presence of a protected species could expose them to liability.

“There aren’t that many species where everyday people in their backyard can do something to help an endangered species,” said Jake Li, who leads efforts to list endangered species at the U.S. Fish and Wildlife Service. “That’s, to me, one thing that makes monarchs so different and why we want to put a heavier thumb on the scale of incentives for people to help us conserve the species.”

The fate of the proposal will ultimately depend on the new administration in Washington. Under Donald J. Trump’s first presidency, wildlife officials found that monarchs met the criteria for listing under the Endangered Species Act, but they were not placed under protection because other species were deemed to have priority.

There is some debate among scientists over the status of North American monarchs and what is driving observed declines in wintertime populations. To assess the species, a team of federal biologists reviewed hundreds of studies and conducted their own modeling, said Kelly Nail, a biologist with the Fish and Wildlife Service who helped lead the effort.

The team estimated that over the next 60 years, North American monarchs east of the Rocky Mountains have a 56 to 74 percent probability of hitting the point where extinction appears inevitable. For those to the west, that probability was 99 percent.

The primary drivers affecting the butterflies, the assessment found, were the loss and degradation of breeding, migratory and overwintering habitat; exposure to insecticides; and the effects of climate change.

“It’s not any one of those in particular, it’s these key threats working in combination with each other that we think are causing this decline,” Dr. Nail said.

Wildlife officials, conservationists and many monarch scientists are calling on the public to help by planting food for monarchs: native milkweeds, which the caterpillars rely on, and a variety of other native flowers that bloom throughout the warmer months to offer nectar for the adult butterflies. Tropical milkweed is best avoided, experts say, especially in areas where it does not die back during the winter, luring monarchs to keep breeding instead of migrating.

The proposal punts on action related to pesticide use, asking for public comment on what measures are warranted.

Activities like ranching, agricultural work and gardening are protected by language that allows for the management of milkweed and nectar plants, even though it could result in monarch deaths. The proposal does not allow killing monarchs for the conversion of natural grasslands, shrub lands or forest without a permit, a condition that could lead to restrictions on developers.

The danger to monarchs, scientists agree, is not global extinction. Populations of the species exist in the wild outside of their native North American range; they’ve been introduced by people or blown by winds to places as distant as Hawaii, Spain and Australia.

What’s at stake is their remarkable migration, which can span up to 3,000 miles between overwintering grounds in central Mexico and summer breeding grounds into Canada. If the migration collapses, the butterflies would likely persist in certain areas of the Southern United States, several scientists said, but their numbers would be greatly diminished.

In 2022, the International Union for Conservation of Nature’s Red List, the scientific authority on the status of species, announced that it had listed the migratory monarch as endangered, but later reclassified it as vulnerable, a less acute category. Canada listed the species as endangered in December 2023. In Mexico, it has a status of “special protection.”

Greg Mitchell, a research scientist with the Canadian government who studies monarchs, visited their overwintering grounds in Mexico last year, where he expected to see butterflies coating the trees. Instead, he said he found himself in what felt like “an empty cathedral.”

“I’ve been two previous times and seen millions, the tree branches drooping,” Dr. Mitchell said. Last year, he didn’t see a single cluster. “It was devastating,” he said. The winter count would turn out to be the second-lowest on record, apparently driven by hot, dry conditions in the United States and Canada that reduced the quality of milkweed and nectar plants.

The monarch’s return to Mexico each year holds great cultural significance among Indigenous communities there, where the butterflies are associated with visiting ancestors, said Rebeca Quiñonez-Piñón, who works on monarch recovery at the National Wildlife Federation.

“Losing the migration means losing deep-rooted traditions, and that’s huge,” Dr. Quiñonez-Piñón said.

Some monarch researchers say concerns for the species, and even the migration, are overblown.

Insect populations tend to fluctuate sharply, they note, and monarchs have bounced back from alarmingly low numbers before. Butterfly survey data from the summer breeding grounds don’t show the sharp drops observed in the overwintering zones. And those winter counts don’t include populations of butterflies that aren’t part of the migration but could rejoin one day, said Anurag Agrawal, a professor of ecology at Cornell University.

But other monarch scientists are not reassured. Nonmigratory populations have higher rates of disease. Data from the summer counts may be biased because of where it’s collected, they say. And even if the species has rebounded during the summer so far, the butterflies are only as strong as their weakest links.

Public comments can be submitted until March 12, 2025.