Painted lady butterflies swarm North County

In spring, a painted lady butterfly begins moving north as temperatures become too warm in Mexico. Along the way, she mates and reproduces./David Tremblay

Painted lady butterflies have found North County San Diego to their liking as they pass through from Mexico to Oregon. It’s the largest such pass-by since 2005, according to butterfly experts. You can easily identify a painted lady butterfly by looking at its orange, brown and white wings, they say.

Wet winter fueled vegetation growth in the Sonoran Desert in Mexico, giving caterpillars a lot to eat have allowed the caterpillars gone wild to go wild with explosive growth and colorful swarms as far as the eye can see.

“The conditions were just perfect,” said Tom Merriman, Director at Butterfly Farms in Encinitas. “I mean there could be over a billion of them, we don’t know. I’m hearing people from Palm Springs to Vista.”

The Mexican butterflies have been spotted from Escondido to Vista to Fallbrook in recent days. However, it’s hard to predict when and where they’ll be throughout the next few weeks. Catch them when you can.

“You’re going to see butterfly after butterfly after butterfly,” said Merriman, referring to the good times when butterflies fly by free. “Every two, three seconds you’re going to see another butterfly coming through.”

Millions of the two-inch butterflies, which can be found around the world, have recently been spotted across North county, zigzagging across roads, parking lots and backyards. The butterflies are heading north on a one-way trip that will end in a few weeks when they lay eggs and die.

The increased presence of painted lady butterflies, a non-endangered native species, is being triggered by a wet winter that has fueled vegetation growth, giving caterpillars plenty of primroses, desert lavender and other plants to eat, experts say.

Related to, but smaller than the stately monarch, the painted ladies were traveling at about 20 to 25 mph headed north to Oregon where they’ll breed, lay eggs and then die; the next generation will continue on north.

“Their caterpillars eat a whole range of herbaceous plants, so when it rains, there’s a whole lot of food for them,” said Michael Wall, vice president of science and conservation, and curator of entomology for the San Diego Natural History Museum to the San Diego Union-Tribune. “ If they stay in the same place, they’ll eat all the food…. It could be in that area that they’re coming from the desert and trying to get to the lowlands where there’s more stuff flowering.”

Under the right conditions, they can number in the hundreds of thousands to upward of a million, Wall said. The last time North County saw vast clouds of the butterflies was in April 2001, when painted ladies made a similar trek across North County.

Observers throughout the region noticed the recent trajectory, and posted videos of the phenomena on Facebook groups Monday afternoon, showing cloudy skies dotted by clusters of butterflies.

Besides the ones that appeared at Daley Ranch in Escondido, viewers at San Diego Zoo Safari Park in South Escondido, as well as Valley Center, San Marcos, and as far away as Menifee, also reported swarms of painted ladies. Painted ladies made an earlier appearance in the desert over the weekend, according to news reports from Palm Springs.

Painted lady butterflies, which look similar to monarch butterflies, are not migrating butterflies, since they have no plans of returning home, according to Douglas Yanega, senior museum scientist of the Entomology Research Museum at UC Riverside.

The butterflies, which can travel a few hundred miles north, sometimes don’t make it very far if they flutter into oncoming traffic.

The bright yellow residue left behind on car windshields and bumpers comes from a chemical compound in their intestines,

Southern California Sees Largest Painted Lady Migration Since 2005/Ecolife

Butterfly populations can shift year to year based on rainfall, Yanega said.

Jim Cornett, lead ecologist for the Palm Springs-based JWC Ecological Consultants, said the initial appearances of painted lady butterflies are in northern Mexico. Some of them stay behind in Mexico to keep the population intact. But others start moving north.

Each successive generation of the butterflies heading north will lay eggs until they die off as far north as Idaho. They fly in that direction, he said, because their genes tell them to move away from the sun and fly toward darker skies.

People took to social media to document the insects fluttering around California. The butterflies travel from the deserts in Mexico and fly as long as their fat reserves last before breeding. Generations of the insects can reach all the way to the Pacific Northwest.

“We’ve been waiting for them to get up here, but they haven’t shown up yet,” said Arthur M. Shapiro, a professor at the University of California, Davis’ Department of Evolution and Ecology, College of Biological Sciences, which is near Sacramento.

“Years of tremendous wildflower blooms typically are really big painted lady years,” he said, adding that the last really big one was in 2005 with estimated billions of butterflies.

The entire North American population of painted lady butterflies migrates to west Texas and northern Mexico during the winter. As caterpillars, they feed on desert annual plants — their favorites are the families of mallows, borages, and thistles and their relatives — and then once butterflies, they begin traveling north.

Painted Lady, Vanessa cardui, with Zinnia flower/Jim Mayes

They can live up to six weeks, but most don’t live that long. There will be waves of migration as the first generation makes it to northern California, they breed and then the next generation makes the trip to the Pacific Northwest, Shapiro said.

On the way back, the next generations of butterflies will begin making the trip south. In Calfornia, the largest number of butterflies are expected on the eastern side of the Sierra Nevada, Shapiro said.

Painted lady butterflies can travel fast. “They can pace cars at 25 miles per hour,” Shapiro said.

And they are good at generating body heat through muscle contractions, which allows them to fly at lower temperatures. The painted ladies have the highest observed altitude record among all butterflies at around 22,000 feet, he said.

For more about the butterfly scene visit Butterfly Farms at Encinitas

1 Comment on "Painted lady butterflies swarm North County"

  1. This was the most informative article I found about the butterfly “bloom” we just experienced. Thanks very much for all the great info; nicely done!

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