The painted lady (Vanessa cardui) belongs to the same family of butterflies as the monarch (Danaus plexippus). Like the monarch, this species migrates in large numbers through California, particularly after a wet winter. Unlike the monarch, painted ladies do not have a spectacular mass return trip in the fall; or at least their return trip is not as widely publicized. However, sufficient numbers of these butterfies apparently return in order to maintain the population. Migration generally occurs during February and March in a northwest direction from desert regions of the United States and northern Mexico. Their flight may reach 30 miles per hour, and individuals may fly more than 100 miles in a day. They fly six to twelve feet above the ground and often hit the windshields of cars. The yellow splatch on your window is their fat supply for the long journey. They typically rise over large obstacles such as buildings, rather than flying around them. According to Arthur Shapiro (Professor of Evolution and Ecology at UC Davis), the butterflies are migrating from their winter breeding grounds on the Mexican border to the Central Valley and foothills, where they will breed, feed and lay eggs. The trip takes roughly three days in good weather. The resulting caterpillars feed on various weeds, such as thistles, mallows and fiddlenecks (Amsinckia). Butterflies resulting from breeding in the Central Valley region will migrate northward to breed again in the Pacific Northwest.