The Postman (Longwing), called the Common Postman to distinguish from the similar Small Postman, is one of the Heliconian family and native from Central America to northern South America. It has many forms and subspecies over its range, mimicking the many forms of the Small Postman as well as other Heliconians that predators have learnt not to eat.
The "standard" form (ssp. rosina), if there is one, also shared with the Small Postman, is the black background with one red vertical bar on each forewing and a horizontal white bar on the hind wing. It is named Postman after the black with red uniforms that postmen used to wear. Male and female have a similar appearance but there are many variations, subspecies and even hybrids.
Since the Small Postman is not much smaller, both having a wingspan around 70-75mm (wingspan of the Common Postman can vary from 65 to 95mm), there are two other ways to differentiate Common and Small Postmen's "standard" form from the underside (not infallible): the Common has three red spots near the body on the hind wing (as in photos above left and above right but not that above centre) compared to four spots for the Small and the white bar on the wing does not go as far as the outside edge on the Common (and not always on the Small).
The "standard" form also comes with "piano key" edging, above/below, both in the Common and in the Small Postmen (and some other Longwings).
Like other Heliconians, adults not only drink nectar but also eat pollen (shown on tongue above) which improves their lifespan from several days to 2-3 months.
Caterpillars eat Passion Flower vines which makes them and the adult butterflies unpalatable to predators.