One man noticed a butterfly had nearly disappeared from San Francisco, figured out exactly why, and started their comeback in his own backyard. Tim Wong is an aquarium biologist at the California Academy of Sciences. The California pipevine swallowtail vanished from the city for the same reason a lot of butterflies vanish: habitat loss. The caterpillars eat exactly one plant: California pipevine, Aristolochia californica, and nothing else. As the city grew, the vine mostly went with it, and the butterfly had nowhere to lay eggs. Wong found one of the last pipevines in San Francisco growing in the botanical garden in Golden Gate Park. He got permission to take cuttings. Then he built a screened enclosure in his backyard, big enough to let the butterflies fly and court normally. He started with 20 caterpillars gathered from outside the city. He's been raising and releasing them back into the botanical garden ever since, and the population there has grown enough that people now see them flying in the park. All it took was one guy deciding to give a shit about a butterfly most people hadn't ever met.