The Red-spotted Purple caterpillar is about 2 inches long when mature. It is brown with 2 large light tan humps on the thorax and a white section (saddle-like pattern) in the middle of the abdomen. There are 2 smaller yellow-orange humps on the 2nd abdominal section. The head is tan and warty. Two long brown antler-like horns extend out behind the head and appear to be slightly clubbed (photo C). It is very similar to the Viceroy caterpillar, but is less spiny and the yellow-orange humps are larger. The individual shown here pupated overnight and had formed a chrysalis by the next morning (photos D, E & F). Eight days later the chrysalis had turned all black as shown in photo G. The wing-span of the adult butterfly is 3 – 3 3/8 inches. Dorsally, it is black with a brilliant blue irridesence. The forewing has 4 small, orange submarginal spots which tend to fade with age. Ventrally, both wings have 2 rows of pale blue broken lines around the margin and orange and pale spots around the bases of the wings. The hindwing has a squarish shape.