SAN FRANCISCO (KPIX) — This spring, the dramatic return of a locally rare, blue iridescent butterfly dazzled onlookers at the San Francisco Botanical Garden in Golden Gate Park.

Neighbor John Gale, who visits the garden often, took in the spectacle.

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“We’ve never seen anything like this,” Gale said. “This has been fantastic.”

The California pipevine swallowtail — native to San Francisco — saw its population decline drastically over the years.

Pipevine Swallowtail Butterfly

A California pipevine swallowtail butterfly in San Francisco. (CBS)

But Tim Wong, also known as the “Butterfly Whisperer,” has led the effort to bring it back.

“That really has finally started to pay off,” said Wong.

KPIX showed the swallowtail caterpillars in a report last August.

And now, the caterpillars that we photographed last year have turned into butterflies and, on a sunny day in May, you could see lots of them, thanks largely to Wong’s dedication.

Caterpillars on a Leaf

Caterpillars of the pipevine swallowtail on a leaf in San Francisco. (CBS)

A California Academy of Sciences aquatic biologist, Wong discovered that the rare butterfly only eats one kind of plant — the California pipevine.

That plant is not easy to find but it does grow at the San Francisco Botanical Garden.

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Wong took plant clippings home a few years ago and successfully populated thousands of California pipevine swallowtails in his backyard.

He used what he learned to help improve and expand the butterfly’s food source in the garden.

“By creating habitat here, we’ve really created a sanctuary where they’re finally almost common here in the garden,” Wong explained.

Visitors say there’s nothing common about what they’re now seeing in the California Native section of the Botanical Garden.

They see California pipevine swallowtails thriving — clusters of males chasing females.

You can also observe their life cycle: females laying tiny eggs — even a caterpillar or chrysalis.

“You feel immersed in their world. You feel like you’re just a part of it,” reflected Brendan Lange, director of visitor experience and marketing at the botanical garden.

For Wong, who has studied native butterflies for 20 years, it’s a labor of love.

“It’s really kind of magical,” he said.

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If you would like to plant California pipevine in your garden, it’s sold at the San Francisco Botanical Garden and it takes three to five years for the plant to get big enough to support the butterfly’s food needs.