Things are shaping up for 2019 to be another massive migration year for Painted Lady butterflies. These are the small orange-and-black butterflies that often get mistaken for Monarchs, and when abundant, fill the skies and surprise everyone by their sheer numbers.
First, a bit about me: I’ve been enthusiastic about Painted Ladies and other butterflies in the genus Vanessa for a long time, and I maintain a citizen science website where people help me keep track of their whereabouts, and that’s how I learned about some of what I'm sharing here.
The first Painted Ladies began appearing in the desert Southwest around late January and early February, and their numbers quickly grew. Large numbers of migrants have been spotted in numerous locations in southern California, southern Nevada, southwestern Arizona and northwestern Mexico since February 15. Although they are generally migrating northward, people in different parts of the Southwest have seen local migration waves headed west, northwest, or northeast.
Now the ongoing Painted Lady migration is well underway, after a seeming delay in some areas due to cool weather. Large numbers were passing through Palm Springs, California on and before March 2, and some of these butterflies were observed flying westward by a friend who was visiting there at the time. They became abundant in the Las Vegas area around March 4, and continue to be active there, according to reports I’ve received via iNaturalist. Most recently, an enormous swarm was flying northward through the Los Angeles area on March 11 and 12. Painted Ladies are now widespread throughout southern California, including in the Anza-Borrego Desert, where they were observed on March 3, and where an extensive northward migration was underway in adjacent Borrego Springs on March 11. In Yuma, in the southwestern corner of Arizona, Painted Ladies have likewise been flying in huge numbers for the last two to three weeks, mainly in a northwestern direction. The entire outbreak was likely triggered by unusually heavy local winter rains associated with the current El Niño event, followed by prolific blooms of desert flowers that provide nectar for the butterflies and profuse growth of food plants for their caterpillars. Whenever this happens, Painted Ladies take advantage of these conditions, breed prolifically, and head off to seek new pastures.
The migration itself is nothing new. Painted Ladies set off from their wintering grounds in the Mojave and Colorado deserts of southeastern California as winter gives way to spring. They travel roughly the same path every year, flying northwest to Sacramento en route to Oregon, Washington and beyond. (They’ve been spotted as far north as Alaska.)
What’s unusual this year is the number of two- to three-inch butterflies making the journey. Scientists say there haven’t been this many Painted Ladies traversing the state since 2005, when the population climbed to about 1 billion.
Scientists were bracing for a butterfly collapse. Now they’re everywhere.
“When they are scarce nobody notices them,” said Art Shapiro, an ecologist at UC Davis who has been tracking butterflies in the state for nearly 50 years. “When they are abundant, everyone notices.”
What will happen next? And will this outbreak - already far surpassing the typical ones occurring every few years - remain mostly limited to the Southwest and West? Or is this just the start of another phenomenal Painted Lady explosion to match the continent-wide migration of 2017?
Although conditions are favorable for this generation to multiply and migrate, what seems to precipitate the rare extensive and enormous continent-wide migration waves throughout summer and fall is for the next several generations in their turn to encounter optimal conditions to thrive and breed - timely rainfall, abundant nectar plants, abundant larval food plants - wherever they might go. If that happens - and it's still not certain at this point - we could be looking at another phenomenal year for Painted Ladies throughout the United States. We'll just have to wait and see.