Close-up of the wing of a Monarch Butterfly (Danaus plexippus). Lepidoptera wings originate in the larva as internal sacs. They are supplied with air during their development through a system of tracheae. When they finally form, the paths of the main tracheae and their branches become sclerotized and form tubular veins (pathways for the tracheae, nerves and blood vessels). Veins also provide support to the wings and are of great importance in classification.