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March 13, 2019, 3:19 GMT
By Phil Helsel
Southern California is in turmoil thanks to an annual migration of butterflies known as the painted lady. In recent days, the skies of some areas has been filled with winged creatures.
People have used social media to document insects floating around California. Butterflies leave the deserts of Mexico and fly as long as their fat reserves remain before breeding. Generations of insects can reach the Pacific Northwest.
"We are waiting for their arrival here, but they have not arrived 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.
"The extraordinary flowering years of wildflowers are usually very great years of painted ladies," he said, adding that the last was in 2005 with estimated billions of butterflies.
Shapiro said that he had reports about butterflies, Vanessa Cardui, in Temecula, north of San Diego, in the Anza-Borrego Desert National Park, and in Pasadena and Coachella Valley.
The entire North American population of painted butterflies migrates to western Texas and northern Mexico during the winter. As caterpillars, they feed on annual desert plants – their favorite families are the families of mauve, hedgerow, thistle and their parents – and then, once the butterflies have started, they head north.
They can live up to six weeks, but most do not live as long. There will be waves of migration when the first generation goes to northern California, they will breed, and the next generation will go to the Pacific Northwest, Shapiro said.
On the way back, the next generations of butterflies will begin their journey to the south. In Calfornia, the largest number of butterflies is expected on the east coast of Sierra Nevada, said Shapiro.
"The south side is never as big as a big migration from the north," he said.
A similar phenomenon occurs in Europe, with some butterflies traveling south across the Sahara in Africa and others in Ethiopia and Eritrea, then migrating to the north of the Mediterranean.
Painted woman, Vanessa cardui, with Zinnia flower.Jim Mayes / Getty Images
Painted butterflies can travel quickly. "They can move cars 25 miles to the hour," Shapiro said.
And they are able to generate body heat through muscle contractions, allowing them to fly at lower temperatures. The painted ladies have the highest observed record of all butterflies at about 22,000 feet, he said.
The size of migrations in the north is often linked to the proliferation of wildflowers in the desert, as heavy rains in this region contribute to the growth of host plants, Shapiro said. Desert State Park of Anza-Borrego said this week many parts of this park have had great displays of wild flowers.
Only a few types of birds catch butterflies on the wing, most being eaten when they are cold, flying slowly or in mud puddles on the ground, he said. And the numbers are on the side of the butterflies. "The birds that eat butterflies will quickly get satiated," he said.
"Yesterday, March 11, we celebrated the anniversary of the arrival of the Davis front in 2005," Shapiro said. "I thought it would be really cute if they had the same date this time, but that did not happen."