Vanessa cardui migrations take place at high altitude, which explains why these migrations are seldom witnessed. "V. cardui" is known for its distinct migratory behavior. In California, they are usually seen flying from north to northwest. These migrations appear to be partially initiated by heavy winter rains in the desert where rainfall controls the growth of larval food plants. Painted lady migration patterns are highly erratic and they do not migrate every year. Some evidence suggests that global climatic events, such as el Niño, may affect the migratory behavior of the painted lady butterflies, causing large-scale migrations. Based on experimental data, the
American painted lady has none. "V. virginiensis" also uniquely features a white dot within the forewing subapical field, set in pink on the underside and usually also in the dorsal side's orange field. The largest spot in the black forewing tips is white in "V. cardui", pale orange in this species, and orange in the West Coast species. The latter also has a purer orange background color of the dorsal side, as opposed to the darker and (especially in "V. virginiensis") redder hue of the other two. A less reliable indicator is the row of black eyespots on the dorsal submarginal hindwing. In