This is a male Monarch Butterfly (see black spots in hindwings), Danaus plexippus, not the Viceroy Butterfly, Limenitis archippus. The Vicery is distinguished by slightly smaller size and the transverse black line in the hindwings. These two butterflies are not an example of "Batesian mimicry," where the Viceroy would simply be protected by strongly resembling the unpalatible Monarch. They represent "Müllerian mimicry" because the Monarch is bitter tasting due to its caterpillar having fed on milkweed and the Viceroy contains unpleasant Salicylic acid (an aspirin-like substance) due to its caterpillar having fed on willows. Through their mutual mimicry, each butterfly is protecting the other through their strikingly similar appearance. Found at the Metropolitan Beach Metropark Nature Area.