The colorful insects leave the Mojave Desert for Oregon in the Pacific Northwest every year during their annual migration, but this year their sheer numbers are surprising scientists, according to the San Francisco Gate.
"In 2005, we had a similar outbreak," professor of evolution and ecology at the University of California, Davis, Arthur M. Shapiro, told the Gate. He estimated the population at around a billion.
"They arrived here on March 11. I thought it would have been great fun if they arrived here on March 11 again, but they didn't,” he said.
As insect populations around the world seem to be in a drastic decline, such a large number of migrating butterflies might belie the disappearing insect problem, but that’s not necessarily the case.
A wet winter with heavy rains has caused an explosion in the painted lady butterfly population this year, Shapiro said, thanks to an abundant food supply in the desert where they lay their eggs.
He expects the numbers to be similar to the 2005 numbers, in the millions, if not a billion again.
The butterfly, which is frequently mistaken for the monarch because of the similar colors, can move as fast a 25 mph and can go for days without stopping, Shapiro told the Gate.
The painted lady is one of the most pervasive butterfly species in the world and is found on every continent except Antarctica and South America, according to National Geographic.
It can migrate up to 2,500 miles over mountains, seas and deserts and can travel at a much higher altitude than other insects.
Scientists still know very little about insect migration in general and painted ladies in particular, but Californians sure enjoy the winged creatures’ annual trek through the Golden State.
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