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The adults come in two distinct forms, the most recognizable one with two evenly curved, bold black lines across the forewing, the other with the lines more faint and thin. The dark-lined form was once thought to be a distinct species (ponderosa B. & McD.). Very similar to M. decorata, but rippertaria lacks the contrasting dark submarginal band distal to the PM line. Decorata also usually has a thin white area bordering the outer margin of the PM line of the hindwing, absent in rippertaria. The typical form of rippertaria is reminiscent of M. neptaria, but neptaria has a two-toned PM line (dark with a light distal border). The PM line is also much more sinuous in rippertaria. Until recently North American rippertaria were treated as a separate species, M. hebetata, and were placed in the genus Semiothisa; hebatata is now considered to be a North American subspecies of rippertaria. (Scoble, 1999)

McGuffin (1972) noted that the green phase of the larva produced adult males and females of the typical colour form, while brown larvae produced males and females of the typical and dark-lined form. Adults lay eggs on the upper surface of willow leaves; they hatch in about eight days. Larval development takes about 31 days, with pupae overwintering. (McGuffin 1972).

Larvae feed on willow (Salix sp.), but it is not clear if more than one or a few species are suitable; given the species' wide geographic range, it is likely a generalist on Salix species. A single collection on aspen (Populus) likely indicates a wandering larvae or an error.(Prentice 1963).