Like most underwings, C. amestris has a brightly colored hindwing and brownish-gray forewings, the wingspan is 1.6-1.8in (4-4.5 cm). The forewings have a blotch that strongly resembles a kidney shape, beyond that the wing has mixed wavy lines. The hindwings have two wavy black lines separating a yellow-orange coloration. The caterpillar of this species is bluish white with a yellowish coloring on the dorsum, or top side. It also has an orange band along with 7 thin black lines on its sides.