Tim Wong, an aquatic biologist at the California Academy of Sciences, helped bring the California pipevine swallowtail back to parts of San Francisco by raising it in his backyard and restoring the one plant its caterpillars can eat. The butterfly is not endangered as a species, and he did not save it from extinction, but he did help a striking local population return to a city where it had become very hard to find. His method is a useful lesson in how urban conservation actually works.
Who Tim Wong is
By day Wong cares for marine animals at the California Academy of Sciences in Golden Gate Park. Butterflies were his childhood hobby. Speaking to CBS San Francisco, he said native butterflies had "kind of always a part of my life growing up", and he joked that he can almost think like one. That intuition earned him the nickname "Butterfly Whisperer" on social media, where he shares photographs of caterpillars, chrysalises and freshly emerged adults.
His interest in this particular species began when he noticed how rarely pipevine swallowtails were seen in the city, despite once having been part of the local fauna.
Meet the pipevine swallowtail
The pipevine swallowtail (Battus philenor) is a large black butterfly with shimmering iridescent blue hindwings. It ranges widely across the eastern and southern United States and into the Southwest, and there is a separate, isolated population in central California. Californian adults are smaller and hairier than their eastern relatives and are usually treated as their own subspecies, Battus philenor hirsuta.
The species has a remarkable chemical defence. Its caterpillars feed only on plants in the genus Aristolochia, the pipevines, and absorb toxic compounds called aristolochic acids. The toxins pass on to the adult butterfly and make it unpleasant for birds to eat. Several other butterflies, including the red-spotted purple and the dark female form of the eastern tiger swallowtail, have evolved to look like it and gain protection from the resemblance.
Why it vanished from San Francisco
In California, the caterpillars depend on a single native vine: California pipevine, Aristolochia californica. As the city grew, that plant largely disappeared from San Francisco's gardens and green spaces. Without it, female butterflies have nowhere to lay their eggs, and a population cannot sustain itself no matter how many flowers are available for adults to sip nectar from.
Butterflies are also sensitive to small changes in a city. Paving over a vacant lot, clearing a tangle of vines along a fence or tidying a park edge can remove the last patch of a host plant from a neighbourhood without anyone noticing.
This is a pattern seen with many specialist insects. The adults may be able to travel, but the next generation is tied to one host plant. Lose the plant and the butterfly goes with it.
How the backyard project worked
Wong took a cutting of California pipevine from a botanic garden in Golden Gate Park and grew the vines at home. He then built a screened enclosure in his yard, designed to mimic the conditions the butterflies prefer, keep out predators, encourage mating and let him watch every stage of the life cycle.
To start the colony he collected about 20 caterpillars from private gardens around the Bay Area where the species still survived. Inside the enclosure they fed, pupated and emerged as adults that mated and laid eggs on the pipevine. Generation by generation, the numbers grew.
Wong then began moving young caterpillars into Golden Gate Park, where pipevine had been planted for them. Reports from 2016 said he had released thousands, and CBS noted that he had also planted pipevine in the garden on the Academy's living roof. Original reports also said he regularly brought caterpillars to the San Francisco Botanical Garden; we have not been able to confirm current details of that arrangement.
Separating the story from the headlines
Many viral versions claimed that one man "single-handedly saved a species from extinction". That overstates it. The IUCN lists the pipevine swallowtail as Least Concern, and across most of its range it is common. Even in California the subspecies survives in many places outside San Francisco.
What Wong achieved was more local and still valuable: he helped re-establish a population in a city where it had become rare, by providing both the insects and the habitat they need. How large and self-sustaining that population becomes depends on whether enough pipevine continues to grow in parks and gardens, which is why habitat matters more than any single release.
What gardeners can learn from it
- Start with the host plant. Nectar flowers feed adults, but caterpillars need specific plants. For pipevine swallowtails in northern California, that means native Aristolochia californica. Some exotic pipevines sold as ornamentals can be harmful to the larvae.
- Plant for your own region. Ask a local native plant society or botanic garden which host plants suit your area and the butterflies that live there.
- Skip shop-bought releases. Conservation groups warn that releasing butterflies bought online can spread disease and mix genetically distinct populations. Wong worked with local stock and local knowledge, and moving wildlife is best left to people coordinating with land managers.
- Avoid pesticides on and near host plants, since caterpillars are exactly the insects many sprays are designed to kill.
Wong's project shows that one determined person can make a real difference in a city, as long as the work starts from what a species actually needs.
Sources: CBS San Francisco: 'Butterfly Whisperer' reviving rare San Francisco species; Mental Floss: Saving gorgeous butterflies, one egg at a time; Wikipedia: Battus philenor; Good News Network; Tim Wong on Instagram.
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