Up to 1.4 inches long. Prefers cabbage, broccoli, and cauliflower but also feeds on turnip, kale, collards, radish, mustard, horseradish, and lettuce.
Young caterpillars feed superficially, leaving the upper leaf surface intact.
Larger larvae leave holes in the leaves. Commonly bore into the center of the cabbage head. Typically leaves masses of wet, greenish brown excrement deep among leaves. Overwinter as pupae attached to host plant debris. Adults emerge as early as March and lay eggs singly on cultivated host plants, if available.