Every spring, swarms of orange butterflies take over Southern California. The annual migration of painted lady butterflies (Vanessa cardui) usually peaks in mid-March. That's when they leave their winter residence in western Mexico and head to the Pacific Northwest for the summer to breed.
Butterflies are often spotted around Los Angeles, San Diego, and Santa Barbara. Their largest congregations can be witnessed where wildflowers grow, like in Anza-Borrego Desert State Park, the Coachella Valley, and in particular, Thousand Palms Preserve. Butterflies love nectar from desert plants such as thistles or mallows that are abundant there. The largest number of painted lady butterflies arrive in the years of desert super-blooms. A super-bloom usually follows a wet and rainy winter. In 2005, over a billion butterflies were registered in Southern California. Vanessa cardui is famous for its bright orange coloring and ability to cover long distances. It has been seen as far north as Alaska. The biggest hazard for painted ladies, as well as for other butterflies, is the heavy use of pesticides by farmers in fields and private gardens. Their population is also threatened by global warming.