AdultThe wing pattern of the Milbert's Tortoiseshell cannot be confused with that of any other butterfly. Males and females are almost identical, but male forelegs are hairier than female forelegs.
Immature StagesEggs are green and conical, with a flattened base and a rounded top, and 8-9 vertical ribs. First instar larvae are yellow green, with rows of black tubercles. Each tubercle has a long black barbed hair. Mature larvae are black on the top half, and yellow green on the bottom half. They are thickly sprinkled with small yellow white or white dots and fine whitish hairs, producing an overall greyish appearance. The body is covered with branching black spines. There is a greenish yellow line down each side, with another line of brighter orange yellow dashes above it. The spines coming from the greenish yellow line are also greenish yellow. The underside of the body is greyish green. Pupae are generally brown with numerous brilliant metallic gold points, but are highly variable. Pupae that are parasitized by ichneumonid wasps have dull red abdomens, and the thorax and head are polished gold tinged with green (Saunders 1869c; Gosse 1883; Edwards 1885c).
SubspeciesThe nominate subspecies, A.m. milberti (Godart, ) (TL: Philadelphia, PA) occurs throughout BC.