Tom Turpin
Professor of
Purdue University


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Flies in the face of fashion

What's Buggin You Now?





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Lights Can Be Fatal Attraction to Night-Flying Insects

If we want to compare things that appear to be drastically dissimilar, we can sum it up by saying, "They are as different as night and day." This saying is often repeated to describe almost anything. Children, work environments, political parties and even performances of sports teams can be compared with the analogy between night and day on this earth.

You don't have to be a geophysicist to understand that this popular idiom has to do with the rotation of the earth. When the earth is pointed toward the sun, we have light. When the earth rotates away from the sun, it turns dark. Of course, the difference is not always as clear as night and day. There is an intermediate period. Tevya, the milkman in "Fiddler on the Roof," sang about it in " Sunrise , Sunset."

Life on earth has always had to cope with the regular cycle of day and night. Living things from plants to animals behave differently when the sun shines. Plants use sunlight to produce food through the light-dependent process of photosynthesis. That can't happen at night, so plants use hours of darkness to complete other biological processes.

Animals, on the other hand, are divided into two groups, according to the day and night cycle. Some animals are called diurnal; they are active during light hours. Many birds fit in this category. This is why we see birds going to roost when it starts to get dark. A high percentage of insects, including the butterflies, are also diurnal.

Nocturnal creatures are active in the dark. We are all familiar with night-flying owls and bats. Raccoons, skunks and opossums also prowl during the night. This is why some mornings bring an abundance of road kills of these animals. Many insects, including beetles, mosquitoes and moths, are also night active.

For millions of years on this earth, days were light and nights were dark. Of course, some nights have always had a bit more light than others, thanks to the moon. The amount of moonlight does vary according to the phase of the moon. But, in general, night-active creatures still have to function in darkness.

Humans have changed that. We are diurnal creatures by nature. Biologically, we are not equipped to function in darkness. We can't see in the dark. So, we solved that by producing our own light to illuminate nighttime activities. First with fire and then with harnessed electricity, humans have turned night into day, at least in some localities.

Such artificial light has created a problem for some insects. Most of us have noticed that a porch light soon has lots of insects flying around it or resting on the wall in the area. We also notice that light fixtures in our home can harbor a number of dead insects. Even an illuminated flashlight seems to be a target for a flying insect. There is something about a light that attracts insects.

There is no good biological reason that insects should be attracted to lights. Nor is there a good explanation of why insects end up at lights. But we know that they do, by the millions. A reasonable hypothesis to explain the phenomenon of the "moth to the flame" is that that night-flying insects get confused in the presence of a point source of light. Instead of flying by the flame, they fly toward it.

Insects had evolved for millions of years when point sources of light at night were absent or rare. In those times, insects went flying about at night without encountering points of light. But in the modern world, the night-flying insects are faced with localized lights. The result is a congregation of insects around lights.

Some insect predators, bats and night hawks, for instance, have discovered that night lights are good hunting places for insects. We once had a toad that took up residence under the pole light in our yard. The old toad didn't have to look far for an insect meal; insects just fell from the sky.

We don't understand why this insect behavior exists, but we do use it. For instance, we put a light source in front of an electric grid and call it a bug zapper! We also put out black lights to capture insects as a method for estimating populations or even to use in collections. In each case, the light turns out to be a "fatal attraction" for the insect.



Writer: Tom Turpin
Editor: Olivia Maddox