Morpho didius, the giant blue morpho, is a Neotropical butterfly belonging to the subfamily Morphinae of family Nymphalidae.

It is considered, by some authors, to be a subspecies of Morpho menelaus.

Morpho didius has a wingspan reaching 150 millimetres (5.9 in), making it one of the largest of Morpho species.

The dorsal side of the wings are iridescent and metallic blue, and the forewings are quite elongated.

The larva feeds on palm trees.