Simulated pollen as a means of deception
Some orchids instead have a sort of pseudo-pollen, similar in consistency to pollen that is edible for their pollinators. The insects, usually bees, then pick up and eat the substance. Dressler also noted the presence of wax on the callus of the labellum of some Maxillaria species that could be used by some bees to build their nests.
In other cases, orchids appear to promise nectar, but don’t actually produce any. Some species, including Calypso, found in our peat bogs, have a plume of yellow hairs resembling edible pollen at the tip of their false anthers.
Plants with moveable parts are always fascinating – just think of the active traps on insect-eating plants. Although the motion is mostly passive on orchids, the way that some flower parts move to facilitate pollination is very interesting.
The labellum on various orchids lowers when a pollinator lands on it, making it easier for pollinia to be deposited or collected. Some Pleurothallis species have hairs or appendages that quiver in the wind, making them especially attractive to flies. The Porroglossum and a few other genera have a hinged labellum that drops down toward the gynostem as soon as there is any pressure on the base of the gynostem that supports it. The only way out for the insect is to push past the stigma and the rostellum, where it deposits some pollinia and picks up more. After a few minutes, the labellum returns to its initial position, ready for its next “victim.”
The ejection of the pollinia of the Catasetum is impressive: it is triggered as soon as something (e.g. the tip of a pencil) touches a seta near the sticky viscidium—a substance that requires vigorous effort to remove, such as rubbing the stigma of another flower and thus leaving the pollinia behind.