When the bald eagle became an endangered species, the chemical that was killing it was banned. When federal officials added the gray wolf to the list, they outlawed hunting wolves. But what happens when the endangered species is something as small as the rusty patched bumblebee?

The yearslong fight over how to save the bees from extinction after their sudden and massive die-off now centers on habitat — how much the bees need and whether it should be subject to special rules. How the battle between regulators and environmental groups plays out could set the standard for how federal protections are applied to other bees, butterflies and important pollinators that are well on their way to becoming endangered.

While the bees named for their rust-colored coats have lost some of the flowers, grasses and trees they need to survive to housing developments and more intensive agriculture, they haven't lost enough over the last 20 years to explain why about 90% of them have died.

Because the amount of available habitat hasn't changed much since the late 1990s, the U.S. Fish and Wildlife Service decided this fall that it will not designate "critical habitat" for the bees, which would have provided them an extra layer of protection.

Several national and local environmental groups decried the move, saying that managing specific areas and keeping certain places free from pesticides are the only ways to stabilize the population.

Three of those environmental groups, the Natural Resources Defense Council, the Center for Biological Diversity and the Friends of Minnesota Scientific and Natural Areas, recently filed an intent to sue Fish and Wildlife, a required step under the Endangered Species Act to give the federal agency 60-day notice before going to court.

The agency drew a false distinction between habitat loss and other threats that are killing the bee, said Lucas Rhoads, staff attorney for the Natural Resources Defense Council.

"One of the threats is disease and parasites, but we know the only way their immune systems can stay strong enough to fight off those diseases and parasites is if they have high quality habitat with flowering plants free from pesticides to get the best nutrition," he said. "For Fish and Wildlife to just throw up their hands and say that more habitat isn't going to help doesn't make sense."

Fish and Wildlife Service officials did not return phone calls seeking comment.

The rusty patched bee, Minnesota's state bee, has disappeared from more than 99% of its native range and is now seen only in a handful of places, including around the Twin Cities.

As recently as the late 1990s, the bees were abundant in the fields, forests and grasslands of 28 states.

The die-off has been primarily caused by pesticides and disease, according to the Fish and Wildlife Service. The losses have been made worse because habitat loss and climate change have also stressed the animals, the agency said.

A critical habitat designation wouldn't create refuges for the bees or ban development or farming.

It would highlight priority areas that could get special regulations, such as limiting the use of certain pesticides such as neonicotinoids that have been particularly harmful to bees, or requiring developers or road builders to offset potential harm to bee populations by planting corridors of native flowers.

Because the bees have flexible diets and eat from a wide variety of native flowers and plants, nearly all of the vegetation they need to recover is still widely available, the Fish and Wildlife Service wrote in its decision to deny critical habitat.

"The availability of habitat does not limit the conservation of the rusty patched bumblebee now, nor will it in the future," the agency wrote.

Those plants may technically be in the ground, but if they're doused in pesticides, they are useless to the bees as habitat, said Lori Ann Burd, environmental health director for the Center for Biological Diversity.

"You can look at a field and say that's habitat, but if the field is poisoned to them it's not," Burd said.

"It's not just about losing one wetland or paving one area, anymore. We're in this new era with the pollinator crisis, and we have to determine what the landscape-level changes are going to look like, if they're ever going to bounce back."

Greg Stanley • 612-673-4882