Southern California bears witness to the annual migration of painted lady butterflies and this year is no different with many people staring in wonder as the skies are filled with the winged creatures.
People shared pictures and videos of the insects fluttering around California. The butterflies come from the deserts of Mexico and continue to fly as long as their fat reserves last before breeding. Whole generations of them can reach up to the Pacific Northwest.
Arthur M. Shapiro, who is a professor at the University of California, Davis’ Department of Evolution and Ecology, College of Biological Sciences, near Sacramento, said, “We’ve been waiting for them to get up here, but they haven’t shown up yet.”
“Years of tremendous wildflower blooms typically are really big painted lady years,” he added, saying that the last big one was in 2005 when billions of butterflies flew in.
Shapiro said he has received reports of the Vanessa cardui butterflies in Temecula, north of San Diego, and in Anza-Borrego Desert State Park, as well as in Pasadena and in the Coachella Valley.
The whole North American population of painted lady butterflies migrates to west Texas and northern Mexico during winter. When they are still caterpillars, they eat desert annual plants with their favorites being the families of mallows, borages, and thistles and their relatives. Once they become butterflies, they start migrating north.
Their life expectancy is six weeks up most don’t live that long. Several waves of migration will occur. As the first generation makes it to northern California, they will breed, allowing the next generation to make the trip to the Pacific Northwest, said Shapiro.
As they make their way back, the next generations of butterflies will start making the trip south. In California, the biggest number of butterflies can be expected on the eastern side of the Sierra Nevada, explained Shapiro.
“The south side is never as big as a big northern migration,” he said.
Europe experiences a similar phenomenon with some butterflies flying south across the Sahara in Africa and others to Ethiopia and Eritrea before they migrate back north across the Mediterranean.
Painted lady butterflies are fast. “They can pace cars at 25 miles per hour,” Shapiro said.
Because they are also good at generating body heat through muscle contractions, they can fly at lower temperatures. Painted ladies hold the record for highest observed altitude among all butterflies at roughly 22,000 feet, he added.
Heavy rains in the desert contribute to the growth of host plants and the blooms of wildflowers there are tied to the size of the northern migrations. Anza-Borrego Desert State Park stated that many parts of the park were experiencing great displays of wildflowers.
Not many types of birds can catch the butterflies as they are flying. Most are eaten if they are cold or flying slowly or are caught in mud puddles on the ground, Shapiro said. But the birds will easily get their fill with the huge numbers of butterflies. “The birds that do eat butterflies will very quickly get satiated,” he said.
“Yesterday, March 11th, was the anniversary for when the front reached Davis in 2005,” Shapiro said. “I thought it would be really cute if they arrived the same date this time, but it didn’t happen.”
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