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In the hills of San Francisco, a nature-focused nonprofit organization works to restore and maintain a rare butterfly’s habitat.
If it’s the third Saturday of the month, it’s a Green Hairstreak Corridor workday for Nature in the City, a nonprofit that fosters biodiversity in San Francisco.
The group established the corridor in 2007 to save a tiny emerald-green butterfly, which once lived all over San Francisco and its peninsula to the south but was believed by many to be extinct.
That’s when local butterfly expert Liam O’Brien, a member of the organization’s steering committee, spotted the tiny green butterfly amid rocky outcroppings in Golden Gate Heights while surveying the city’s butterflies. Nature in the City worked with neighbors, the city, and community groups to get the project started.
Now, nearly 20 years later, the group has successfully restored — and even expanded — the butterfly’s ecosystem. In a 26-square-block-stretch in Golden Gate Heights, which has so many steep streets the city built outdoor public stairways to make it easier to get around, Nature in the City created new habitat in 15 sites, including public stairways; community, private, and school gardens; and four natural areas. The first of San Francisco’s mosaic stairways, which depicts nature’s creatures in the sea, land, and sky, is along the corridor, as are the mosaic Hidden Garden Steps, two blocks away.
On a recent weekend, executive director Amber Hasselbring invited the public to walk the corridor. The day began with a tour of Nature in the City’s nursery, where native plants are propagated for the corridor. Volunteers plant seeds in the nursery, tend them in their own backyard gardens, and then transplant them to habitat sites after removing invasive non-native plants.
While walking the corridor, Hasselbring pointed out native plants the nickel-sized butterfly favors: the coast buckwheat (round clusters of tiny flowers, usually white, on a shrub-like plant that likes rocky slopes and sandy soil), seaside daisy (a pink or lavender daisy with a big yellow center), and deerweed (yellow flowers on tall stalks). All are perennials with low-water needs, ideal for San Francisco, where rain is rare.
I’ve seen it many times: Someone sees a green hairstreak butterfly for the first time, and then connects this sighting to the work of volunteers and neighbors or to an iNaturalist observation.
– Nature in the City executive director Amber Hasselbring
An eagle-eyed woman spotted a green hairstreak on a slope in Golden Gate Heights Park, a wooded area whose hilltop dune offers panoramic views of the city and Pacific Ocean, during the walk. “Found it!” she shouted happily, as rapt onlookers quickly surrounded her.
“It may not seem that extraordinary to restore habitat so one butterfly species can survive; however, when Robert M. Pyle coined the phrase ‘extinction of experience’ decades ago, he realized that when people lose that awe and connection with nature, something changes in their relationship with nature,” Hasselbring says, quoting the ecologist who wrote The Thunder Tree: Lessons From an Urban Wildland (on Amazon and Bookshop) and bemoaned the loss of human connectedness to the natural world due to the exponential growth of living in cities.
“I agree wholeheartedly! I’ve seen it many times: Someone sees a green hairstreak butterfly for the first time, and then connects this sighting to the work of volunteers and neighbors or to an iNaturalist observation,” she adds, referring to the app that helps amateur naturalists identify animals and plants. “That experience helps shift their perspective to one of care, stewardship, and awe.”
Nature in the City’s work is increasingly important: A March 2025 study by The Xerces Society for Invertebrate Conservation, which Pyle founded in 1971, found that 22% of butterfly species have been lost from 2000 to 2020, and 1.6% are being lost each year. Pyle named the society after the first butterfly species to go extinct due to human activity, the Xerces Blue. The bright-blue butterfly with a white polka-dotted underside once thrived in the dunes of western San Francisco before its habitat was destroyed in the late 1800s and early 1900s, when housing and the Golden Gate Park replaced the dunes; it was last sighted around 1942.
The best-case scenario for the Green Hairstreak Corridor project, Hasselbring says, would be its “adoption not only by neighbors and volunteers, but also other city agencies and departments promoting it, valuing it, adding it into their outreach materials. And that San Francisco as a whole and its residents and agencies decide to expand the corridor’s biodiverse habitat to other appropriate lands, like gardens, parks, and throughways.”
How You Can Help
Nature in the City supports more than just the green hairstreak butterfly — it also restores and maintains crucial habitat for birds and other wildlife across San Francisco. Want to get involved? You can participate in monthly workdays at different sites in the city, planting seedlings and cleaning out invasive species, or cultivate seeds at the organization’s nursery while learning how to propagate native plants in your own backyard. You can also help out with fundraising, outreach, administrative, and communications efforts. Learn more and sign up to volunteer at natureinthecity.org/volunteer.
