Those Obnoxious Flies—More Useful Than You Think?

MOST of us consider flies to be either a nuisance or a downright danger to society. But biologists are discovering that flies, bothersome as they may be, are more useful than we might think.

Many species spend much of the day visiting flowers, fast-food outlets that offer their insect clients both nectar and pollen. Some flies that can extract the nutrients from pollen—no mean feat in itself—depend on this high-energy food to develop their eggs.

While visiting one flower after another, the flies inevitably pick up sticky grains of pollen, which attach themselves to their bodies. One fly that was carefully examined by biologists had 1,200 grains of pollen on his body! As more research has been done on the pollination role of flies, scientists have discovered that some flowers depend on them for their survival.

The magazine Natural History describes a series of experiments carried out in Colorado, North America. Common muscoid flies, which resemble houseflies, were dusted with bright colors so that they could be tracked easily. After monitoring their daily activity, the researchers were surprised to discover that for some wildflowers the flies were more important pollinators than the bees and that they ranged a lot farther than bees.

How important is the flies’ work? Some flowers were covered over with netting so that they could not be visited. These flowers produced no seed at all—in sharp contrast with the fruitful ones nearby that were pollinated by flies. Although some flowers were principally pollinated by bees, in the case of other species such as wild flax or wild geranium, at some elevations the flies performed over 90 percent of this work.

What was the conclusion of Carol Kearns and David Inouye, two of the researchers? “For many wildflowers in the Colorado Rockies, then, flies outshadow bees, butterflies, and hummingbirds . . . Without these insects, which most people find slightly repulsive, many of the wildflowers that make visiting an alpine meadow so delightful would fail to set seed.” No doubt about it, flies have their uses!