It is well known that animal-pollinated plants usually offer nectar or pollen to reward vectors for pollen transfer. While nectar is a kind of sugar water, pollen is protein-rich, a must-need nutrient for bee babies. The honey humans consume is made by female bee workers. Fifty years ago, German scientist Stefan Vogel first identified that droplets are non-water miscible 'nectar' but lipids in some flowering plants, discovering the so-called oil-flower, which offers oil as a reward for female bees.