This species mimics the monarchs appearance to avoid heavy predation by birds who mistake this tasty mimic for the distasteful monarch. Caterpillars feed on willow leaves and mimic bird droppings in appearance. Butterflies lack dark-colored wing veins and the white spots on the wings are more diffuse. In the spring, surviving adult butterflies begin migrating north, breeding and developing through 2 to 4 or more generations as they spread north. About 100 million members of the last generation produced in the fall migrate to Mexico and live for about 9 months.
Caterpillars have chewing mouthparts.
Adults have siphoning mouths. Caterpillars feed exclusively on milkweed. Adults feed on nectar from numerous wild flowers. The monarch butterflies are distasteful to birds because of chemicals obtained from caterpillar feeding on milkweed leaves. See also Butterfly Gardening in Texas .