The painted ladies are on move.

Butterflies.

Scores of painted ladies (Vanessa cardui) are now migrating north from their overwintering sites near the U.S. Mexico border. 

A honey bee and a painted lady sharing a Spanish lavender blossom. (Photo by Kathy Keatley Garvey)

"Fascinatingly, they arrived in Prescott, Ariz., the same day (as the ones spotted in Benicia)," said butterfly expert Art Shapiro, distinguished professor of evolution and ecology at the University of California, Davis. "I think they're all from south of the border." The annual migration north varies, but can take place as early as late January and as late as mid-April.

The painted ladies spend the winter in the desert, where in the late winter, they breed on desert annual plants, Shapiro says. The adults emerge in February or March and immediately migrate into the Central Valley and foothills, where they breed. Around May, here in the Central Valley, you'll see the caterpillar offspring munching on borage, thistles, fiddleneck and mallows. Then the adults head toward the Pacific Northwest.

"The painted lady moves northward in a generational wave as the season progresses," Shapiro says on his website. "Frequently it disappears altogether from the lowlands in summer. Beginning in August the movement reverses and butterflies head south toward the desert wintering grounds."

"There is no evidence that this species overwinters successfully anywhere in our area, except for very rare individuals maturing in midwinter from really late autumnal larvae." 

The painted lady migration may not be as popular as the monarch (Danaus plexippus) migration, but it's fascinating just the same.

Shapiro, who has monitored the butterfly population of California's Central Valley for 42 years, will be speaking at noon on Monday, March 24 on "Ecological Communities and the March of Time" in the Commonwealth Club, 595 Market St., San Francisco.     For program detail and registration, please see  the club website.  His talk is open to the public. For a discount, access the website and use the coupon code, "friendsforshapiro," said spokesperson Chisako Ress (chisakoress@gmail.com).