Much has been written about the benefits of the intimate relationships between plants and their pollinators. Plants provide the nectar (sugar) reward for the services of an animal that moves pollen from one flower to another. Nectar isn’t the only reward, however; animals collect that pollen for their own uses.
So many flowers, so much pollen, it sounds like an easy way to gather food. But nothing in nature is that easy.
The pollen coat is so tough that it can resist decay for millions of years in bog and sediment deposits. It cannot be broken down by freezing, grinding, or boiling in acid. So how does a mere animal with a relatively soft, chitinous exoskeleton manage to break into the rich interior of a pollen grain?
By tricking the pollen grain into opening its germination pore, just as it would if it landed on the sticky surface of a flower stigma.
Immersing pollen in a sugar solution in an insect’s gut is all that is needed to initiate the germination process, which normally would result in the growth of a tube from where the pollen grain landed on the flower stigma down into the ovary. In another chamber of the insect’s (or bat’s or bird’s) digestive tract, then, digestive enzymes can attack the interior of the pollen grain through the germination pore, and release the carbohydrate, lipid, and protein stored there. It turns out this pseudo-germination trick is used by most pollen eaters. (Read more about this here.)
But Heliconius butterflies exhibit a different strategy.
Butterfly mouth parts are adapted for sucking nectar not ingesting pollen. To get around this potential disadvantage, Heliconius butterflies collect pollen on the tip of their proboscis, secrete some of the nectar they have sipped onto the dry pollen mass, and then agitate the mass with their proboscis for many minutes, while the germination process begins. The volume of nectar that is eventually re-ingested then contains amino acids and fatty acids that the butterflies need for egg production. (Read more about this here.)
Perhaps other butterfly species do this as well. If a curious young grad student hadn’t noticed that Heliconius butterflies sometimes spent 10 minutes at a flower instead of their normal 3 seconds, this amazing behavior might have gone unreported.