This colorful caterpillar grows to 1 5/8 inches when mature. It has a black background with cream to orange wavy lines, numerous white dots and orange and cream-colored branching spines. The head capsule is dark red. The adult butterfly has a wingspan of about 2.5 inches. The summer form is mostly orange above with scattered dark spots on the forewings and all dark hindwings. The wings of the summer form are a mottled brown below. The winter form (seen in fall and spring) is mostly orange above with brown and orange spots and lavendar edgings. The wings of the winter form are a uniform reddish or violet brown color below. The hindwing tails are longer than any other “commas.” Underneath the hindwing, the silvery “comma” has an offset dot which forms a questionmark.