California Super Bloom Causes Millions of Migrating Painted Lady Butterflies to Fill the Sky

The skies of Southern California have become filled with millions of painted lady butterflies in the biggest migration event since 2005, thanks to recent heavy rain.

Experts say the state's unusually wet winter and cooler than normal February have enabled plants to flourish in a rare super bloom event, which in turn has provided plentiful food for butterflies.

"The more plants, the more butterflies," Art Shapiro, a professor at the University of California, Davis's Department of Evolution and Ecology, College of Biological Sciences, told the Los Angeles Times. "So any year you have a real big bloom in the desert is potentially a big year for painted ladies."

Shapiro told NBC the migration is the biggest since 2005. He estimates that billions of butterflies appeared during that migration.

The Times reported that hundreds of the insects have been spotted in such locations as the 105 Freeway in Los Angeles.

Also known as the Vanessa cardui, the medium-sized insects are known for migrating long distances. They can be identified by their pale orange upper wings, which feature black tips with dots of white. Their undersides are pale and emblazoned with peacock feather-like blue eyespots.

In the winter, painted ladies head to west Texas and northern Mexico, according to NBC. The eggs they lay turn into caterpillars and transform into butterflies, which head north until their fat reserves are spent before breeding. After reaching Northern California, those insects will breed, and their spawn will make the journey to the Pacific Northwest.

But they haven't arrived yet, Shapiro, who is based in Sacramento, told NBC. However, he has been notified of swarms in the city of Temecula and Anza-Borrego Desert State Park; to the north and east of San Diego, respectively and further north in the Coachella Valley and in Pasadena, just outside of Los Angeles.

Doug Yanega, senior museum scientist at UC Riverside's Entomology Research Museum, told Los Angeles Curbed there are currently caterpillars "everywhere" in southern California's deserts. And he and his colleagues counted at least 100 butterflies in one minute during their lunch break at the institution, which is in the south of the state.

He told Newsweek: "Millions came northward from Mexico, and now, after one generation, they certainly number in the billions."

"Anecdotally, long-term resident entomologists I know are saying it's been about 20 years or so since they've seen such numbers."

Because it can take about one month for caterpillars to turn into butterflies, the sightings could continue for up to three months, Yanega said.

Excited locals have shared footage on social media of the butterflies taking to the skies.

There are about 1 billion Painted Lady butterflies migrating from Mexico to Oregon, just now passing through SoCal. This was 25seconds I stopped to video.

— Kathy P (@KKPofCC78) March 12, 2019

Front row seats to the painted lady #butterflymigration! #butterflies #paintedladies #Irvine #OrangeCounty

— South Coast Research (@UCSouthCoast) March 12, 2019

James Danoff-Burg, the conservation director at the Living Desert Zoo and Gardens in Palm Desert, told the Los Angeles Times he encountered a kaleidoscope of butterflies while he was riding his bike in the resort city of La Quinta in Riverside County.

"They were flying parallel to me, just bobbing along as I rode past the date palms," he said. "It was absolutely magical. I felt like a Disney princess."

Yanega told Newsweek the phenomenon is "one of the few 'worry-free' examples of animal population outbreaks in nature."

"They are a native species (not exotic, like Gypsy moths in the Northeast), and—despite their broad diet—they almost never feed on commercial crops, so they're not a pest. It's hard to think of many other cases where an animal population can attain such numbers and not have a major negative impact on either the ecosystem or on humans, especially agriculture.

"Essentially, the ecosystem is converting extra plant material (resulting from strong winter rains) into extra butterflies. Animals that feed on butterflies will benefit, while we get to sit back and enjoy the show."

The scenes come as experts lament the decline of California's butterfly populations in recent decades.

"It was a terrible—perhaps even catastrophic—butterfly year at all elevations, and no, we don't know why," Shapiro wrote in a report about 2018.

This article has been updated with comment from Doug Yanega.

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A painted lady butterfly sits on an echinacea plant. Southern California has witnessed a surge in sightings of these insects. Getty Images