Nectar supplies sugar but very little nitrogen, and butterflies that rely on it alone must build their eggs from reserves accumulated as larvae. Heliconius butterflies escape that constraint. An adult gathers pollen grains on the outer surface of its coiled proboscis, kneads the accumulated load into a clump using coiling movements, and releases saliva onto it. Amino acids leached from the grains are then taken up in the resulting fluid.
The consequences are behavioural as well as nutritional. Heliconius adults can live several months rather than weeks, continue laying eggs across that period, and show trapline foraging, revisiting the same reliable pollen sources in sequence day after day. This trapline behaviour is associated with enlarged mushroom bodies in the brain, and Heliconius have become a model for studying insect spatial memory.
Heliconius melpomene also participates in Müllerian mimicry with Heliconius erato, the two species converging on matching warning patterns that shift together across geography. The genetic basis of these switches, involving a small set of pattern genes, has been mapped in detail, though how the races stay distinct where they meet is still worked on.