A few days ago my eyes began to itch. Grass and tree pollen trigger allergies that will continue until the first frost.
But pollen is a necessary evil. It is essential for the reproduction of flowering plants. Pollen originates in the stamens of flowers. It is essentially the sperm that must reach another flower's pistols to fertilize its eggs. When that happens, seeds and fruits form via sexual reproduction.
Many plants, especially grasses and trees, are pollinated by the wind, which carries pollen from one flower to another. Allergy sufferers inhale windborne pollen incidentally, and symptoms ensue.
Pollination by animals is what I find more interesting. According to the U.S. Fish and Wildlife Service, animal pollinators fertilize more than 150 different kinds of agricultural products including apples, blueberries, melons, peaches, potatoes, pumpkins and almonds. The value of natural pollination is estimated at about $40 billion annually.
Worldwide, about 1,000 species of plants that humans use for food, beverages, fibers, spices and medicines rely on animal pollinators. That list includes coffee, cacao (chocolate), vanilla and tequila.
The mechanism of wind pollination is self-evident. Wind blows pollen from one flower to another and the pollen (sperm) finds the eggs. Pollination by animals requires direct contact between pollinator and flower.
To attract pollinators, flowers must provide a lure -- nectar. Insects and some birds and mammals find it irresistible. Some pollinators, such as honeybees also use pollen as a food source.
When a pollinator visits a flower, pollen grains attach to their bodies as they sip nectar. When they visit the next flower, some pollen rubs off to fertilize the flower. And they pick up new pollen from the new flower. Since most pollinators visit thousands of flowers every day, this is an effective strategy that works even when there is no wind.
Pollination is classic mutualism. Flowers provide food to the pollinators, and flowers get fertilized. It's win-win.
To appreciate the diversity of pollinators, observe some blooming flowers to enter the world of pollination ecology. Myriad bees, wasps, butterflies, moths, beetles, true bugs and flies transfer pollen from flower to flower. Hummingbirds pollinate the flowers they visit, too. And though we have only the ruby-throated hummingbird here in the east, hummingbird diversity increases to the south and west. For example, 18 species of hummers are found in Arizona, and 132 species of hummingbirds inhabit Ecuador. All can pollinate their nectar sources.