West Coast lady it lacks obvious ventral eyespots on the hindwings; there are two large ones on "V. virginiensis" and four small ones on "V. cardui". Like the latter, it also lacks a white dot in the pinkish-orange subapical field of the ventral and dorsal forewings. Its upperwing coloration has the purest orange of the three; the American painted lady is usually quite reddish. A less reliable indicator is the row of black eyespots on the dorsal submarginal hindwing. These are usually of roughly equal size in "V. cardui" and lack blue centers, though the summer morph may have a few tiny ones.
Urophora cardui arvense", during the host's growing season. After hatching, the larvae burrow into the stem of the plant and form a gall (or swelling). During maturing, the larva will be 98% of its full body weight, and appear as an adult. The larvae pupate in early spring for 24 to 35 days, and appear reddish brown, but are still inside the gall. The fly goes through a tunnel formed in the gall during June to October. Urophora cardui Urophora cardui or the Canada thistle gall fly is a fruit fly which, contrary to its common name, is indigenous to Central Europe