Thousands of painted lady butterflies have been passing over the Peninsula this month as they migrate north from desert areas along the U.S.-Mexico border, according to scientists at UC Davis.
Painted lady butterflies, known by the scientific name vanessa cardui, are about 1 1/2 inches to 2 1/4 inches wide. They are orange with a black, lacy pattern on the wings and a series of blue "eye spots" on the lower-lobe wings. Their migration is typically seen in the early spring weeks through March.
Northward-migrating painted ladies can travel the distance from Bishop to Davis in three days, surviving on yellow-fat reserves in their bodies, according to a UC Davis researcher's Web page on the butterflies.
The butterflies do not stop to feed or mate until they have burned up their reserves, carried over from the caterpillar stage. They fly in a straight line from southeast to northwest, like "bats out of Hell," and go over obstacles rather than trying to go around them, the researchers wrote. Beginning in August, the movement reverses and butterflies head south toward their desert wintering grounds.
In 2005, the population was so dense that their numbers impeded traffic in desert regions, researchers said.