These migrations are sporadic and often enormous, and often follow rainy periods in these deserts. The other, V. c. kershawi , occurs in Australia and New Zealand and strays into Fiji. I have found that in Iowa, V. cardui prefers more open areas such as prairies and fields, whereas V. atalanta prefers forest margins and parklike areas with more trees. The dorsal side of the wings is orange-patterned. On the underside of the hindwing are five small submarginal eyespots.
Females are generally larger than males.
V. cardui , like V. atalanta , has distinct summer and winter forms. The winter form has entirely black wing spots. A Field Guide to Eastern Butterflies. Houghton Mifflin, Boston. Butterflies East of the Great Plains.