This butterfly belongs to the brush-footed family (Nymphalidae), so called because the forelegs are reduced (vestigial) and are not used for walking. The red-spotted purple is harmless (Batesian) mimic of the noxious pipevine swallowtail in coloration, but lacks the "tails". The caterpillar feeds on willow and other trees such as aspen, poplar and hornbeam.