Urban Pioneers in San Francisco's Canyons

A London Plane tree glows in early morning light in downtown San Francisco.

A London Plane tree glows in early morning light in downtown San Francisco.


Urban Pioneers in
San Francisco’s Canyon

An unlikely tribe of urban pioneers is taking up residence in downtown San Francisco, snatching up unclaimed resources and paying zero taxes. And they dress like they own the place.

The Western Swallowtail Butterfly is a big, dramatic yellow and black diva of a butterfly, the size of a fluttering smartphone. This butterfly looks at the high rises and cookie cutter landscaping of Market Street, but it doesn’t see MUNI buses and commuters. She sees a river valley, a landscape of high canyon walls, intercut with side canyons and sunny glades, thermals to rise and sail on. A river lined by mature London plane trees, and scattered with nectar-bearing flowers. In other words, just the place to start a family.

A Western Tiger Swallowtail butterfly in all its glory. Photo courtesy Mathesont @ flickr

A Western Tiger Swallowtail butterfly in all its glory. Photo courtesy Mathesont @ flickr

Swallowtail butterflies are cosmopolitan and flexible. They live all over the world, and our local variety can thrive on a variety of tree species. But deciduous, riverine trees — sycamores, cottonwoods, aspens and plane trees — are favorites for egg laying. The Western Tiger Swallowtail is not an invasive species. But before 1987, it never lived in downtown San Francisco. Now, like the red-masked parakeets (natives to Peru and Ecuador), these butterflies are thriving in an increasingly green, but unmistakably urban setting.

“We go dumb for pretty.”

Butterflies are the perfect ambassador for urban wildlife. “We go dumb for pretty,” says Liam O’Brien, lepidopterist and vocal advocate for the Swallowtails. And making life a little easier for the butterflies doesn’t take much effort. When companies replant the concrete boxes outside their offices, picking a butterfly-friendly shrub requires no extra money, no extra maintenance, no extra water.

A Swallowtail out for nectar. Photo courtesy siamesepuppy @ flickr

A Swallowtail out for nectar. Photo courtesy siamesepuppy @ flickr

Reimagining Market Street

“The Swallowtails are an easy entry point into a larger conversation about the urban environment,” says Simon Bertrang, the Project Manager for Better Market Street. Coordinating the efforts of five city agencies, Better Market Street is working with community partners and the public to make Market Street a more inviting place, where pedestrians and cyclists are likely to linger. Part of rethinking this urban environment means reframing what role nature plays in the city.

The Market Street Prototyping Festival, April 9–11, will feature 50 projects that reimagine Market Street as a vibrant public space. Among the prototypes will be Market Street as Habitat, celebrating the urban wildlife that live among us, and how to share this space with our wilder neighbors, including the flashy Western Swallowtail.

Non-native plants are just fine, thanks

Recreating a native ecosystem in the Financial District or the Civic Center isn’t going to happen. And as the name suggests, the London plane trees that the Swallowtails gravitate toward are imports from overseas. But laying out the welcome mat for butterflies and other nectar-eaters, like bees, doesn’t take much more than variety. “Lavender isn’t native to California, but now it supports bee diversity,” explains Peter Brastow, Senior Biodiversity Coordinator for the SF Dept of the Environment. “The High Line Park in New York City is not a natural environment, but it’s become an oasis for people and wildlife.”

Huge, beautiful butterflies thriving among the high rises sounds like a San Francisco cliché. But maybe the Western Swallowtail stands for a bigger, older dream in San Francisco. The butterflies came, reimagined what this city could be, and made their own future.

What you can do:

Check out the Better Market Street Prototyping Festival

Make your garden butterfly-friendly

Learn more about these beautiful neighbors