Postman Butterflies (Heliconius melpomene) are tropical butterflies found in Central and South America. They are most common along sunlit forest edges with flowers. I observed this Postman Butterfly on Lantana (Lantana camara) flowers next to a forested area in Alajuela, Costa Rica. Lantana flowers are particular favorites of these and other Heliconian butterflies.
Over their large range, Postman Butterflies have many geographic subspecies with very different markings. The subspecies found in Costa Rica, H. melpomene rosina, is dark brown to brownish black in color with a broad band of orange across each forewing and a stripe of pale yellow along each hindwing. The orange, yellow, and black colors of this butterfly are a form of aposematic (warning) coloration meant to warn potential predators like birds that it is poisonous.
This subspecies of Postman Butterfly is almost identical to the subspecies of another butterfly found in Costa Rica, the more common Crimson-patched Longwing (Heliconius erato petiverana), but these two subspecies can be distinguished in the field by their ventral wing surfaces. The yellow stripe on this Postman Butterfly subspecies does not touch the far edge of the hindwing, while the yellow stripe on the Crimson-patched Longwing subspecies touches both edges of the hindwing.
Throughout their shared range, the various geographic subspecies of H. melpomene and H. erato have come to resemble each other quite closely, forming an amazing Müllerian mimicry complex. Müllerian mimicry is where two or more species in an area share the same harmful or unpalatable characteristics, the same predators, and the same aposematic signals. Both H. melpomene and H. erato are poisonous, preyed on by birds, and although they are both highly variable, their subspecies sharing a particular geographic area are almost identically patterned. To add to the confusion, these two butterfly species can often be seen together.
Adult Postman Butterflies feed on flower nectar and pollen, while their much pickier caterpillars feed only on the leaves of Passionflowers (Passiflora spp.). If you see a Postman Butterfly hovering around a passion vine, you may be able to observe her laying tiny, yellow eggs on the leaves.