The viceroy butterﬂy has a wingspan of about two and one-half to three and one-fourth inches. The upper side of its wings is orange or brown-orange with dark veins and a dark curving line on each hindwing. The wings also have a single row of white spots in the black border. The lower side of the wings is paler than the upper side. The viceroy is similar in coloration to the monarch butterfly, but the monarch does not have the curved dark line on the hindwing and does have two rows of white spots in the dark border. The viceroy adult contains bitter-tasting chemicals (salicylic acid) that the larvae absorb from the willow trees that they feed on. They are often spared from predation because predators do not care for the bad taste and learn to avoid them. The monarch may or may not contain bitter-tasting chemicals from the milkweeds eaten by its larvae and can gain some protection by looking like a viceroy. The viceroy caterpillar is olive-green with a white spot on the back, white sides and a few black spots. It has projections that resemble antennae on the second segment of the thorax.
The viceroy may be found statewide in Illinois, usually along the edges of water bodies and in swampy areas. It ﬂies from April through October with two to three broods produced per year. The larvae eat leaves of various willow species. This insect overwinters in the larval stage in a leaf shelter that it creates.