[1] The genus Latin name Caligo means "darkness" and may refer to the active periods, as these butterflies preferentially fly in dusk.

The specific name illioneus derives from Ilionesus, a Trojan companion of Aeneas in Virgil's Aeneid.

In this large owl butterfly the dorsal sides of the wings vary from light brilliant blue to purplish with dark brown edges, while the undersides have a highly cryptic dull brown color, with huge yellow-rimmed eyespots resembling to the eyes of an owl.

In the early stage the caterpillars are greenish with yellow stripes along the body, about 10 centimetres (3.9 in) long.

The species is native to Costa Rica and it is widespread in most of South America, particularly in Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela.