The front end of a massive migrating butterfly swarm reached Northern California late last week, and the so-called painted ladies are flying through some unexpected places, including San Francisco's Presidio National Park.





"There has definitely been a big spike in the past couple days," Young said. "It's not the millions they're seeing in Southern California, but it's definitely a migration. I've never heard of the masses come through the city itself."


Arthur Shapiro, a professor of evolution and ecology at UC Davis, is an expert on painted ladies and he's baffled by their migration this year.

"Damned if I know," he said. "It blindsided me. This year, they went to the west for whatever reason. The weather patterns have been very different so that might have impacted it. We had an unusually cold February, and we've only seen some warm weather in the last few days."


"The numbers have remained low until yesterday, when I counted over 300 here," Shapiro told SFGATE in an interview Wednesday. "I went out twice. In the morning, I counted one every 90 seconds. That sped up to one per minute in the afternoon. I haven't seen any today due to the bad weather. I expect the flight will not peak until early next week."


Painted ladies are reputedly the most widespread butterfly in the world, and due to their orange and black coloring, they're commonly mistaken for monarch butterflies.


This is the largest migration of painted ladies since 2005, and Shapiro says the insects totaled around a billion that year. Scientists suspect this year's migration to be in the millions.