Monarch butterflies are dying out. Here’s how cities can help.

Planting or allowing a few milkweed plants to grow in residential yards, parks, and empty lots, along roadsides and boulevards, as well as on school, church, and commercial properties, could play a major role in saving North America’s iconic monarch butterflies from extinction, a study from Chicago’s Field Museum shows.

The eastern population of monarchs has declined over 80 percent and the western population is nearly extinct, with just 3 percent of its population remaining.

"Metropolitan areas actually matter for wildlife conservation, and that's especially true for pollinators like the monarch that can survive with very small patches of habitat," says Abigail Derby Lewis, a senior conservation ecologist at the Field Museum and lead author of the paper published today in the journal Frontiers in Ecology and Evolution.

The shocking declines in monarch numbers over the last 20 years came largely because the common milkweed (Asclepias syriaca) is disappearing due to widespread use of herbicides and the loss of field margins and hedgerows. Milkweed is the only plant monarchs can lay their eggs on and the only plant its caterpillar stage feeds on. (Which species of milkweed should you plant? Learn more here.)

More milkweed—a lot more

The United States Fish and Wildlife Service estimates that saving the eastern population of monarchs requires an additional 1.8 billion milkweed plants. In thinking through how and where this could be done, ecologists at the Field Museum in the heart of Chicago decided to look in their own backyards.

Their research team used field research coupled with high-resolution imagery, enhanced by LiDAR —light in the form of a pulsed laser—to accurately map where milkweed already grows across four major metropolitan areas (Chicago, Minneapolis-St. Paul, Kansas City, and Austin) and where there's potential to add to it.

There is little milkweed currently found in residential areas, but yards represent an enormous opportunity to boost milkweed numbers just from the sheer amount of homes, said Mark Johnston, a conservation ecologist at the Field Museum and lead author of the team's second paper, published in the same journal.

That study concluded that cities could support nearly 30 percent of the additional 1.8 billion milkweed plants needed to save eastern monarchs. The rest could come from milkweed on existing protected lands, land enrolled in the Conservation Reserve Program, in rights-of-way status, and land associated with agricultural practices.

These first-ever studies on the milkweed-growing potential of cities are based on the assumption that only two out of every 100 property owners would actually plant milkweed.

Population numbers are so low for the western monarch that they are rarely seen in urban areas. However the lessons drawn from these studies can be applied to metropolitan landscapes in the West.

While everyone loves monarchs, not many love milkweed. It is still on some state’s noxious weed lists and some local weed ordinances require mandatory trimming of plants taller than 10 inches.

Milkweed needs a rebrand

"Certainly having the term 'weed' in the name of milkweed—which isn't a weed—has not helped the reputation of these superstar native plants," says Derby Lewis.

Given that a name change to Monarch Flower is unlikely, a shift in public perception of what is beautiful and appropriate in home landscaping is needed, she said.

Planting pollinator gardens in high visibility places such as the grounds of public buildings, churches, and schools is important. The National Wildlife Federation’s Mayors' Monarch Pledge, where mayors across North America have pledged to add monarch habitat, can provide a strong leadership signal, she said. Montreal, for example, was proud to announce this month that it is the first Canadian city to be granted gold status as a monarch-friendly community.

Often if one neighbor or an institution like a church plants a pollinator garden, others will follow, Johnston said. Such gardens are hugely beneficial for a wide range of wildlife from beetles to birds. These diverse green spaces are also increasingly seen as essential in reducing flooding and cooling urban areas, particularly in an era of extreme weather caused by climate change, he said. Pollinator gardens absorb carbon, as well as help reduce air and water pollution.

“Studies show green spaces make people happier and healthier,” said Johnston. “Property values are also higher and crime rates are lower.”

People need nature. And nature—especially monarchs—need people in cities and suburban areas to transform low-quality green spaces, like lawn grass, into high-quality homes for butterflies and other pollinators, said Derby Lewis.