Monarch butterflies could disappear from North America unless more is done to protect their rapidly vanishing habitats, conservation groups told the Obama administration in a legal petition Tuesday. The filing seeks to list the monarchs as “threatened” under the Endangered Species Act and designate “critical” areas across the country to guarantee the monarchs a place to breed and feed.

Numbers of the black-and-tawny butterflies have dropped by more than 90 percent in the last two decades, according to the Center for Biological Diversity and Center for Food Safety, which led the petition to the U.S. Fish and Wildlife Service. About 35 million monarchs remain, down from more than a billion in the mid-1990s, as their lifeblood -- the milkweed plant -- disappears from U.S. farmlands and prairies.

“Monarchs are in a deadly free fall, and the threats they face are now so large in scale that Endangered Species Act protection is needed … while there is still time to reverse the severe decline,” Lincoln Brower, a conservationist who has studied monarchs since 1954 and who joined the petition, said in a statement.

Butterflies are born every spring and summer in habitats as far south as Texas. Every few weeks, adults flutter north, lay their eggs on milkweed plants and die. The caterpillars feast on the plants, sprout wings and continue the northern migration up to southern Canada. In late summer, monarchs reverse course and fly down to central Mexico, where they pass the winter months.

A handful of factors can disrupt this pattern, including hotter- or colder-than-average springs and summers, drought conditions and illegal logging in Mexico. But by far the largest threat to monarchs is the widespread use of herbicides on America’s farmlands. Since the 1990s, corn and soybean growers have increasingly planted seeds that are genetically modified to resist herbicides like Monsanto Co.'s (NYSE:MON) Roundup weed killer. Using these types of seeds allows farmers to spray herbicide across broad swaths of their fields, a practice that in turn destroys milkweed -- the only plant monarch larvae will eat.

“The areas that are most important to monarchs are the same areas where we grow a lot of corn and soybeans,” Sarina Jepsen, the endangered species program director at the Xerces Society in Portland, Oregon, which also signed the petition, told International Business Times. 

This year, 94 percent of all soybean acreage is “herbicide tolerant,” up from 17 percent in 1997, the U.S. Department of Agriculture’s Economic Research Service reported. Nearly 90 percent of corn acreage is herbicide tolerant, up from just a trace two decades ago.

Largely as a result, monarchs have lost more than 165 million acres of habitat -- an area about the size of Texas -- in the past two decades, a swath that includes nearly a third of their summer breeding grounds, the conservation groups said in their petition. A similar threat is facing other types of "pollinators," including honey bees, birds and bats, which have all seen their populations decline in recent decades.

The Xerces Society is working with conservation groups and farmers to reproduce and distribute milkweed seeds in an attempt to restore monarch habitats. So far, Project Milkweed has produced 35 million seeds native to different agricultural regions. 

Monsanto itself is backing programs to increase milkweed plants along migratory corridors in North America. The St. Louis company is “committed to providing tools and strategies to make farmland more productive and sustainable,” Charla Lord, a Monsanto spokeswoman, said in an email.

The White House in June called for a Pollinator Health Task Force, to be co-chaired by the Secretary of Agriculture and the head of the Environmental Protection Agency. "Given the breadth, severity, and persistence of pollinator losses, it is critical to expand federal efforts and take new steps to reverse pollinator losses and help restore populations to healthy levels," Obama wrote in a presidential memorandum.

Still, conservation groups say more dramatic measures are needed to keep monarch populations from falling further. Declaring the butterflies “threatened,” for instance, would make it illegal to intentionally kill monarchs or destroy their habitat without a federal permit, Jepsen said. It would also open new sources of federal funding for milkweed restoration programs and farmer education initiatives. The Fish and Wildlife Service would have to write an official recovery plan to outline steps for restoring monarch populations.

It could be years before the monarch receives federal protection.

Gavin Shire, a spokesman for the wildlife service, declined to comment on the petition, but said officials would conduct an initial 90-day review. If they find “substantial scientific information” backing the petitioners’ request, then the agency will conduct a 12-month review. “If that review finds that the action is not warranted, we publish our decision and the process ends there,” Shire said in an email.

If officials find the “threatened” status is warranted, however, they could propose a rule, which would undergo a 12-month public comment period. After that, the agency could publish a final rule, or withdraw the petition. “At all stages, the Endangered Species Act requires that we make our decisions on ‘the best scientific and commercial data available,’” he said.

About 30 other butterfly species already are protected by the federal government, out of about 16,000 total protected species.

Losing monarchs, however, would be especially devastating because of how prominently they factor into the national imagination, Tierra Curry, a senior scientist at the Center for Biological Diversity in Portland, Oregon, said in an interview. Monarchs are found in nearly every U.S. state, and the monarch was the first butterfly to have its genome sequenced. American astronauts even reared monarchs on the International Space Station in 2009.

“It’s really important that we protect it, because it is so familiar,” Curry said. “Losing something that was so widespread and common is kind of a wakeup call that we’ve made these huge landscape-level changes.”