James Owen in National Geographic:
Unlike most flowers, roughly a third of the approximately 30,000 orchid species in the world don’t rely on the lure of food to achieve pollination. Instead, the orchids trick insects into performing the task without reward.
Most of these orchids are “food deceptive.” Using bright colors and sweet perfumes, they falsely advertise a free meal of pollen and nectar to attract bees, beetles, butterflies, and other pollinators. (Other of these orchids are even more elaborate in their cunning, mimicking the appearance and sex pheromones of female insects to lure males looking for a mate.)
More here. (Thanks Margit.)