Painted Lady Butterflies Migrate in Big Numbers through San Diego

On a warm clear day in San Diego, the butterflies came.

"Oooh," said beachgoers in La Jolla. "Beautiful." They watched openmouthed and dodged as hundreds of butterflies, orange and black tipped with white, zigzagged up and over them on their way up the coast.

Painted ladies (vanessa cardui) have returned to Southern California, soaring over beaches, across freeways, and into the northwest on their annual migration route. While the butterflies are not forming the huge clouds that stopped traffic in 2005, they are showing up in greater numbers than they have in a couple of years because of warm temperatures and a relatively wet winter that helps the thistles and cheeseweeds bloom.

"What we normally see about every four, five, six years depending on rainfall in central and northern Baja California, we'll get millions and millions of these things coming through in just tremendous numbers," says San Diego entomologist David Faulkner. "This is the reflection of a pretty good breeding season last year."

The brightly-colored creatures are born in warm, dry areas - in this region, it's Baja California and the desert areas - and head northwest, burning their larval fat along the way, not stopping until they find coastal wildflowers to feed on before mating, laying eggs, and dying. Higher-than-average rainfall means more plants, which means more butterfly outbreaks.

Painted ladies are closely related to the monarch, and like the monarch, they mass migrate through California. Unlike the monarch, however, there is no spectacular return trip. Painted ladies are great travelers; they are also known as "Cosmopolitan" butterflies because they cover nearly every part of the world. Their trip from Baja California into northern California and Oregon is nothing compared to their flight from Morocco over the shark-infested Strait of Gibraltar and across Europe into Britain.

When they are on the move they fly in a straight line, going over obstructions instead of around them, and covering dozens of miles in a day. They don't stop to rest, and unlike many butterfly species, even fly at night, defying the rule that butterflies, which are cold-blooded, need warmth to be active. They fly from the hot desert southeast into the more temperate and humid northwest, usually all at once, says Faulkner. "There's usually one day where there's a peak, and it trails off after that."

While painted ladies are not endangered, their numbers have dropped as the plants they feed on either die out or are developed away, and migration patterns seem to be changing with the climate as they travel either farther north or higher up to find the plants that grow in cooler environments.

Painted ladies are also very difficult to avoid as they go across roads and highways, leaving yellow smears, the vestigial larval fat, across windshields. No car is immune from the onslaught. But painted ladies pass quickly. The next day the onslaught of butterflies had vanished, and only a few wobbled their way northwest in the afternoon sun.

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