Animal pollen couriers demand a wage for their services. Flowers usually reward their pollinators with sweet nectar (nectar is sweetened water produced in specials glands – nectaries – that are usually hidden deep within the floral organs), nutritious oils, or perhaps even pollen itself to eat.
As the animals walk over or shoulder their way down into the flower parts in search of their reward, the plant dusts them with pollen which they then carry off hopefully to the stigma of a another flower of the same type.
Towards that end, plants have evolved a number of different adaptations for attracting insect pollinators.
Color and Patterns as a Lure
To get the attention of insect pollinators many plants produce flowers with bright, showy petals. Unfortunately, humans with a limited scope of vision miss some of the plant world’s best tricks when it comes to flower color and pattern.
We may view a simple white flower and delight in its simplicity. However, bees, able to see ultraviolet light, could see the same flower as glowing blue-green. Other insects might detect dots, rings, and lines on the same flower marking out welcoming landing strips that our vision cannot perceive.
Scent as a Lure
The Arums attract not with color and pattern but with smell. The dead horse arum (Helicodiceros muscivorus) grows on the islands of Corsica and Sardinia in the Mediterranean, often near a colony of gulls.
A gull colony is normally buzzing with blowflies. There is lots of food for the flies and their grubs – dead chicks, broken and rotting eggs, droppings, and decaying fish. At the height of this activity in the gull colony, the arum produces its flower. It is grayish purple, blotched and streaked with pink, covered with coarse dark red hairs and is the size of a dinner plate.
This flower gives off a smell remarkably akin to the stench that comes from carrion. It resembles and smells, in short, like a piece of rotting flesh. The blow flies swarm all over this new dish leaving with fresh loads of pollen to deposit elsewhere.
The African plant, Anchomanes difformis, does the botanical equivalent of lighting a scented candle. In the middle of its flower, A. difformis has a foot-tall structure called a spadix. The plant is able to generate heat within its tissues and this warms the plant to about 40C (104F). The sweet musky odor that results from this heating process wafts off the spadix and attracts the small beetles that pollinate the flower.
Shape and Appearance as a Lure
Form and appearance can serve as an effective lure. The mirror orchid (Ophrys speculum) of the western Mediterranean produces a flower that looks remarkably like the female of a species of large wasp or bee common to the area where it grows. Not only does the flower look amazingly similar to a female bee or wasp, but due to the release of chemicals called pheromones, it smells like a female as well.
If, and when, a male bee finds the flower, he settles upon the lip, grasping it in exactly the same way as he would grasp a female, and tries to copulate. He fails, of course, but in the process, a curved column that houses both male and female organs, descends from the top of the orchid and glues a packet of pollen to the bee’s head. If the next orchid he visits has already dispatched it pollen, then the column will pick up the one he carries and the orchid is pollinated.
In one particular orchid, a bee’s gentle touch causes the stem of the pollen sac to snap like a spring, catapulting the stem and its sticky pollen onto the bee, which is often knocked right out of the flower by the impact.
Some partnerships have developed in which the shape and structure of the flower is so attuned to the shape and structure of a single pollinator that were one to disappear, the other would very likely either starve or remain sterile.
The most extreme and celebrated example of this matching between the anatomies of flower and pollinator is that of an orchid and a moth in Madagascar. The nectar of the orchid lies anywhere from a foot to a foot and a half deep within the heart of the flower. A rare species of hawk moth is the only insect with a proboscis of such a length and as such, is the orchids’ only pollinator.
Plants cast a variety of lures – color, scent, form and appearance – in hopes of luring insects that will ferry pollen to the female structures of their kind.
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