(Giant) Owl Butterfly Caligo sp. (memnon, eurilochus, atreus, euphorbus, idomeneus, etc.)

Owl butterfly - Caligo memnon
Giant Owl butterfly - Caligo eurilochus
The enormous Owl Butterfly, also called the Giant Owl and, less usually, the Cocoa Mort Bleu, has a brown underside with false "eye" spots to deter predators. With wings spread open it mimics an owl's face. There are some 20 similar-looking but different species, all native to forests of Central and South America. The genus name Caligo comes from the calico brown colouring.
Giant Forest Owl butterfly
Giant Pale Owl butterfly
The two most encountered species in Butterfly Houses are the Giant Forest Owl, Caligo eurilochus above left, and the (Giant) Pale Owl, Caligo memnon above right, both from Central America. The Owl Butterfly rarely opens its wings when at rest and, unfortunately, the main variation in the species is on the topside. However, the Pale Owl shows a much lighter forewing when closed.
Giant Forest Owl butterfly topside open
Pale Owl butterfly topside open
Pale Owl butterfly topside open
The topside has iridescent blue or mauve colouring. Left is that of the Giant Forest Owl, which is mainly mid-blue; above right is the Pale Owl. Individuals vary and lose colour with age.
Giant Forest Owl butterfly The Giant Forest Owl's darker forewing. It often has a wider white "iris" round the "pupil" on the eyespot, but not always.
Giant Pale Owl butterfly The Pale Owl's paler leading edge to the closed forewing. (and narrower "iris" sometimes.)
Yellow-edged Giant Owl butterfly atreus Another species - Caligo atreus - the Yellow-edged Giant Owl - the "yellow edge" being on the topside (not visible here)
Owl butterfly
Owl butterfly
Owl butterfly
Close-ups of the face and the "eyespot." Typical wingspan is around 100-160mm.
Owl butterfly eyes An indication of how intimidating the "eyes" can seem - like a predator's face if the Owl is open or coupled.
Owl butterfly The head and true eye
Owl butterfly Size comparison with Morpho