Swarms of butterflies are invading inland sections of Southern California as a result of an unusually heavy migration of a common species making its way from Mexico to the Pacific Northwest to breed, experts say.

About 1 billion butterflies, known as Painted Ladies, are flying at speeds of 20 miles per hour in a northerly direction from the deserts of Mexico to reach breeding grounds in Oregon, said Tom Merriman, a director of Butterfly Farms, a nonprofit in north San Diego County dedicated to restoring the health of butterflies as pollinators.

Many callers have reported being amazed at the volume of these small, yellowish, orange and black butterflies the size of a silver dollar. Reports have come in from the coastal communities, Orange County, Inglewood, San Dimas, Glendora, Pasadena, Burbank, San Bernardino and Palm Desert.

“This kind of large migration is unusual,” Merriman said during an interview from his office in Encinitas. “They’ve laid tons of eggs in the desert, and so there may be over a billion butterflies.”

A painted lady butterfly lands on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

A Painted Lady butterfly rests on a lupine flower near the historic YorbaÐSlaughter Adobe in Chino on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

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A Painted Lady butterfly rests on a plant near the historic YorbaÐSlaughter Adobe in Chino on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A Painted Lady butterfly rests on a plant near an office building in Ontario on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A honey bee approaches a painted lady butterfly perched on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)



A Painted Lady butterfly rests on a plant in Jurupa Valley on Friday, March 8, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A Painted Lady butterfly rests on the ground near a roly poly near an office building in Ontario on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A Painted Lady butterfly rests on a plant near the historic YorbaÐSlaughter Adobe in Chino on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A painted lady butterfly lands on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

A Painted Lady butterfly rests on the wet ground near an office building in Ontario on Thursday, March 7, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)



A Painted Lady butterfly rests on a plant in Jurupa Valley on Friday, March 8, 2019. (Photo by Watchara Phomicinda, The Press-Enterprise/SCNG)

A Painted Lady butterfly pauses its migration on a Spanish lavender plant in a Pasadena garden. (Photo courtesy of Jocelyn Webb Pedersen)

A painted lady butterfly lands on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

A painted lady butterfly (Vanessa cardui) stops for a drink on purple productus ice plant flowers in a Jurupa Valley neighborhood on Thursday, Feb. 28, 2019. The butterflies were migrating north at about 100 per minute at that point. (Jennifer Iyer, The Press-Enterprise/SCNG)

A pair of painted lady butterfly (Vanessa cardui) flit over a rooftop in Jurupa Valley on Thursday, Feb. 28, 2019. The butterflies were migrating north at about 100 per minute at that point. (Jennifer Iyer, The Press-Enterprise/SCNG)



A painted lady butterfly (Vanessa cardui) stops for a drink on bladderpod flowers in a Jurupa Valley neighborhood on Thursday, Feb. 28, 2019. The butterflies were migrating north at about 100 per minute at that point. (Jennifer Iyer, The Press-Enterprise/SCNG)

A painted lady butterfly (Vanessa cardui) pauses in a Jurupa Valley neighborhood on Thursday, Feb. 28, 2019. The butterflies were migrating north at about 100 per minute at that point. (Jennifer Iyer, The Press-Enterprise/SCNG)

A kaleidoscope of Painted Lady butterflies flies over Serrano Creek Park in Lake Forest, CA, on Tuesday, March 12, 2019. (Photo by Jeff Gritchen, Orange County Register/SCNG)

Thousands of painted butterflies are filling the air around Southern California seen here taking a break for a drink on the way through Santa Clarita, CA. (Photo by David Crane, Los Angeles Daily News/SCNG)

Thousands of painted butterflies are filling the air around the San Fernando Valley, seen here pausing at Woodley Park in Van Nuys. (Photo by David Crane, Los Angeles Daily News/SCNG)



Thousands of painted butterflies are filling the air around the San Fernando Valley, seen here pausing at Woodley Park in Van Nuys. (Photo by David Crane, Los Angeles Daily News/SCNG)

A painted lady butterfly lands on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

A painted lady butterfly lands on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

A honey bee approaches a painted lady butterfly perched on a flower in a North Tustin garden on Wednesday, March 13, 2019, as swarms of butterflies invade Southern California as a result of an unusually heavy migration making its way from Mexico to the Pacific Northwest to breed, experts say. (Photo by Mark Rightmire, Orange County Register/SCNG)

Callers to this news group and others who’ve posted on Facebook said they noticed the swarms last week and on Monday and Tuesday of this week.

Mary Ames ran into the migration on Monday outside her home in Temecula.

“A huge migration went over my house between about 4 p.m. and 5 p.m. I’d say at least 100 a minute for the first 10 to 20 minutes, then at a slower rate,” Ames wrote in an email. “Must be some kind of record.”

“I have never in my life seen this sort of migration. They are flying so fast,” said Rene Amy, who witnessed a swarm at the Alice Dog Park at 3026 E. Orange Grove Blvd. in Pasadena.

Amy said he heard from a friend in west Pasadena who saw a swarm pass by his house.

The painted lady butterflies are migrating! At one point we had maybe 100 per minute… but they’re not very big so it’s not dramatic. Jurupa Valley, Feb. 28, 2019. pic.twitter.com/LS0nCMdkGO — Jennifer Iyer (@Jen_Iyer) February 28, 2019

“These things were flying at my vehicle. I didn’t want to hit them,” Amy said.

In Lake Forest, Michele Jones was going about her business on Tuesday — getting her hair done, picking up lunch at McDonald’s — when she was ambushed by painted ladies.

“It was amazing,” she said. “All of a sudden, there was like a million of them coming at me.”

When she got home, even more butterflies were streaming by her windows. Jones had no inkling that her house near Serrano Creek Park is on the Lepidoptera superhighway — she’s never seen anything like it in 27 years of living there, she said.

Jones’ only complaint about the painted ladies is that they didn’t stay longer.

“It is pretty to see them,” she said. “I wish they would stop. I have so many trees and bushes.”

Beach cities residents, including those in Manhattan, Hermosa and Redondo Beach, started noticing the tiny butterflies on Monday afternoon.

Tuesday morning commuters in South Redondo Beach were treated to hundreds of the butterflies flitting about down Esplanade and Pacific Coast Highway.

Real estate broker Alex Smith caught sight of the butterfly swarm in Redondo Beach. He captured the flyover on a Facebook live video.

“All of a sudden there are just thousands and thousands of butterflies,” Smith said on the video. “There are butterflies everywhere. This is crazy. It’s the butterfly apocalypse.”

Smith described seeing hundreds of butterflies flying over the front yard, which were difficult to capture on video.

“They are everywhere,” he said.

Merriman believes the migration may continue for a month or until the butterflies run out of energy.

He advised anyone who sees these fast-moving butterflies to stay out of their way.

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“Let them go. They are determined to go where they want to go. They want to go north, and they are moving pretty quick,” he said.

The Painted Lady butterfly is one of the more common butterflies in North America and is not endangered. They are a distant cousin of the monarch butterfly, which have experienced dramatic declines in recent years, Merriman said.

The large migration was prompted by the plentiful rains this winter, he said. The last previous mega-migration occurred in the spring of 2005 after one of the wetter years ever in California history.

Staff writers Alicia Robinson and David Rosenfeld contributed to this report.