A massive swarm of at least 1 billion butterflies is traveling across Los Angeles and neighboring counties at a breathtaking speed of almost 20 miles an hour, reports said.

The butterfly species Painted Ladies, cousins to the Monarch butterfly, are in a rush to reach breeding areas in Oregon after spending winter in the deserts of northern Mexico, according to Tom Merriman, a director of a butterfly non-profit group in Encinitas, in an interview with the Pasadena Star News. “They’ve laid tons of eggs in the desert, and so there may be over a billion butterflies,” Merriman told the paper.

Social media users in L.A. reported seeing the fluttering insects across the region, from Glendora to the beaches to South-Central L.A. Butterflies floated quickly across Martin Luther King Jr. Boulevard in South L.A. from downtown to Leimert Park.

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Southern California friends: I just sat on the beach in the South Bay for two hours while 1,000s of butterflies flew around and past me. What kind are they? What is happening? #butterflies pic.twitter.com/n1IrEaBy0D — jessica. (@loveheylola) March 11, 2019

The migration is not exactly new and the painted ladies have been spotted as far north as Alaska. “We counted 250 in one hour in the Arroyo Seco, all streaking westward. Quite a sight,” tweeted user L.A. Resident Tourist.

Walked outside to find thousands and thousands of butterflies flying in a constant stream through #redondobeach. Thought it was debris in the wind at first but looks like some sort of migration. Any ideas @NHMLA ? @CBSLA pic.twitter.com/v1Zb8PH7pY — John Schreiber (@johnschreiber) March 11, 2019

Experts said the migration is prompted also by California’s heavy winter rains. Butterflies had actually become scarce in California during the prolonged previous drought, the L.A. Times noted.

* Updated.

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