It’s a sad fact of urban living—when more people move in, if they’re not careful, animals often end up moving out. Such has been the case with the California pipevine swallowtail butterfly, an iridescent blue-green creature that has been driven out of its native range by rampant development.

Over the years, various groups have attempted to reintroduce the butterfly—but although they’ve been fairly successful in Sonoma (where they live in a butterfly garden) and Santa Cruz (where they’ve been spotted near a golf course), the butterflies haven’t been able to make it in San Francisco.

That is, until now. As Vox reported earlier this year, one San Franciscan—biologist Tim Wong, of the California Academy of Sciences—is doing a lot all on his own. Wong, who has been raising butterflies since childhood, has dedicated a large chunk of his backyard to the pipevine swallowtails, building a large, screened enclosure filled with native plants where they can enjoy San Francisco weather without fear of predators.

The bugs are a bit picky—as caterpillars, they eat exactly one plant, the California pipevine, which is also rare. (Other, introduced pipevines, will poison them.) Wong managed to nab some native pipevine clippings from the San Francisco Botanical Garden—with permission, of course.

He then brought in about 20 caterpillars from outside the city, where the species is more present. He watched them eat the pipevine, form chrysalises, and emerge weeks later, as butterflies, to restart the cycle. When he got his first clutch of tiny caterpillar eggs, he incubated them indoors, where they were safe from hungry bugs that could sneak into the mesh enclosure.

Wong has been successful enough to bring thousands of the caterpillars to the San Francisco Botanical Garden, where they live in the “California Native” exhibit.

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