The last two decades have been grim for the monarch butterfly.

There used to be more than a billion black-and-orange monarchs fluttering up from Mexico each spring to lay eggs on milkweed plants across North America. But as we've eradicated those native milkweeds with farming, mowing, and herbicide spraying, butterfly numbers have collapsed 84 percent since 1995. Things have gotten so dire that a new study in Scientific Reports warns the Eastern migratory population of monarchs could dwindle to near-extinction in just 20 years.**

The Eastern population of monarchs could go nearly extinct in the next 20 years

Americans are quite fond of this iconic, speckled butterfly, so, naturally, the prospect of doom has spurred volunteers into action. This year, the conservation group Monarch Watch plans to distribute 200,000 to 300,000 milkweeds for people to plant in their gardens and fields to help monarchs thrive. Some state highway departments, like Texas's, have become more mindful about mowing milkweeds on their roadsides during the spring migration season.

But those efforts aren't nearly enough. John Pleasants, an ecologist at Iowa State University, estimates the United States has lost more than 1 billion milkweed plants since the 1990s — in part due to herbicide spraying on cropland in the Midwest. And we're still losing about 2 million milkweeds each year, particularly when farmers convert grassland to cropland. "There are admirable efforts out there," Pleasants says. "But we still haven't made a significant dent in what's needed."

If we want to avoid a butterfly apocalypse, we may have to get creative. So I was intrigued to hear about a clever recent initiative that the Environmental Defense Fund is trying to set up — a program they've dubbed an "Airbnb for butterflies."

The basic idea would be to create an exchange where investors and conservationists could pay farmers, ranchers, and other landowners to set aside protected space filled with milkweeds and other native prairie grasses along the monarchs' migration route. We still don't know if it will succeed. But if it does help save the monarch from extinction, it could be an innovative model for protecting other endangered species in the future.

How an "Airbnb for butterflies" would work

Every spring, monarchs fly up from Mexico to lay eggs on milkweed plants in Texas and the Midwest, breeding two successive generations as they go. (In the fall, that third generation flies all the way back to Mexico for the winter.) Milkweed is the only source of food for their caterpillars before turning into butterflies. No milkweeds, no monarchs.

Unfortunately, America has lost a lot of milkweed since 1995 — with 70 percent of losses occurring on cropland in the Midwest. Some experts blame modern agriculture. Farmers used to manually clear out milkweeds, which regrew every year. But in the 1990s, Monsanto developed corn and soy varieties genetically engineered to be resistant to herbicides. Farmers could spray more readily, and fields became clear of weeds. Between 1999 and 2010, Pleasants and Karen Oberhauser found, half of all milkweed vanished from the Corn Belt. The number of monarch eggs laid fell 80 percent. (Note: There's still debate over the details here. Other shifting agricultural practices besides herbicides may have caused milkweed losses too.)

So if we want to save the monarch, planting more milkweed in gardens and highway strips isn't sufficient. Someone needs to convince farmers to protect milkweeds on their private land. And there are two big ways to do that.

One is through legal means. Last year, environmental groups filed a petition with the US Fish and Wildlife Service to list the monarch as "endangered" or "threatened" under the Endangered Species Act. If the FWS agrees to list the species, the federal government could conceivably start requiring farmers to limit herbicide spraying — or take other forceful measures. The downside is that this is a sluggish process and is sure to be fraught with controversy.

The other solution would be working through the market — and that's where EDF's "Airbnb for butterflies" comes in. EDF is currently trying to set up a Monarch Butterfly Habitat Exchange in which people and companies could connect with and pay farmers and ranchers to set aside land for milkweeds.

That might entail things like paying farmers to avoid spraying around the edge of their fields. Or planting milkweed on conservation land. "You don't need any one patch [of protected land] to be huge," says David Wolfe, the director of conservation strategies at Environmental Defense Fund. Creating a mosaic of "rented" milkweed strips across the Midwest could be enough to save the monarch. (Preserving the native plants would also help bees and other pollinators, too.)

Why would anyone pay for this? Wolfe argues that chemical and seed companies could be persuaded to fund butterfly conservation this way — in the hopes of fending off an Endangered Species Act listing that leads to more heavy-handed regulation from the federal government. "We know from our experience with energy and chemical companies that they much prefer proactive steps to help a species recover and keep it off the list," he says. "That's a driving force behind habitat exchange."

There's a precedent here with the sage grouse, a chicken-size bird in the American West that has seen similarly perilous declines. In recent years, conservation groups have worked with ranchers, energy companies, and others to develop private initiatives to save the bird and avoid an endangered species listing. A listing, after all, could have led to sharp restrictions on oil drilling, livestock grazing, and construction on Western lands. So everyone was motivated to take preemptive action. (Audubon has a great rundown of those efforts here.)

Wolfe hopes that the monarch exchange can be a similar success story. But it's not easy to set up. EDF is working with scientists to figure out how to assess land in the Midwest — getting a sense for which areas along the monarchs' route would be most valuable to save. And any investors would need assurances that they're paying for actual conservation and not just pushing farmers to spray elsewhere.

EDF is hoping to launch early monarch exchanges in Texas and California by 2017 and then expand outward. If it's a success, the concept could conceivably work in other areas — like with threatened aquatic species in the Southeast. "We believe the idea has broad applicability," Wolfe says.

The underlying idea here is to complement federal conservation efforts. The Endangered Species Act has been remarkably successful at saving many plants and animals from extinction. But the agency in charge remains underfunded, and there's a backlog of hundreds of species awaiting decisions. Legal action can often take years. Adding another protective tool to the mix could be invaluable.

But Airbnb isn't enough. The monarch also faces threats in Mexico.

Other experts I talked to thought the exchange was worth a shot, but they also pointed out just how daunting the challenge is.

Scientists estimate monarch populations by counting the number of trees the butterflies occupy in Mexico each winter. In 1996 to 1997, the monarchs took up 18 hectares of forest; this past year, that was down to just 4 hectares.

Yes, there was a small recovery this past winter that got lots of optimistic headlines, but most experts think that was a random bit of good fortune — warm weather last summer aided the breeding season. And fortune can turn very quickly. A few weeks ago, a storm hit central Mexico, drenching the butterflies in rain. When temperatures then dropped below freezing, a big chunk of the population died out.

"I'm worried that the population will get so small that, with more bad luck, we could lose the whole thing," says Lincoln Brower, a monarch expert at Sweet Briar College. To get the monarchs back on a sustainable path, they'd likely need to bounce back to around 6 hectares in the winter, well above their average for the past decade.

And even if planting more milkweeds can help, it's not the only problem the butterflies face. Illegal logging in Mexico has shrunk the Oyamel fir forests where monarchs reside in the winter. Brower notes that the forests continue to be under severe threat from logging — despite promises by the Mexican government to protect them. Between April and August 2015, he says, there's evidence that illegal logging wiped out some 10 hectares of habitat. "We've seen all these reports about how authorities protected the forests," Browser says. "And it's bullshit. Loggers are still going in and taking out truckloads of timber."

So the monarchs are still in a precarious place. Ingenuity will help, but they'll also need stricter environmental protections — as well as a bit of old-fashioned luck.

** Footnote: In the post above, I'm mostly focusing on the much larger Eastern population of monarchs. But there is also a smaller population of monarch butterflies, west of the Rocky Mountains, that spend their winter in groves along the California coast.

Those Western monarchs have seen a roughly 50 percent decline in population from the long-term average, but scientists have not said that they're at risk of extinction (not yet, at least). The causes of the Western monarch decline are different, but a butterfly exchange could conceivably help there too.

Go deeper: