Painted lady butterfly migration

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

Swarms of butterflies are invading 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 San Dimas, Glendora, Pasadena, Burbank, San Bernardino and Palm Desert.

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

Callers to the Southern California News Group and others who’ve posted on Facebook said they noticed the swarms earlier this week as well as on Friday.

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

“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 around 1 p.m. Friday.

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

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

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

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

“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.

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