Marilyn Tabor, age 11, of Atlanta, Georgia for her question:
Why are insects attracted to lights?
Summer is crammed with mysterious wonders and this seems to be the biggest mystery of all. Old timers tell us that a velvety moth flies into a flame because she cannot resist its fascination. But this suicidal be¬havior seems ridiculous. It seems equally foolish for June bugs and other insects to swarm around street lamps and other lights. Actually, they are not attracted toward lights at all. They do so because they misjudge them.
Many millions of years ago, insects learned to navigate by light from the stars, the moon and the sun. It seems fantastic, but they in¬vented this celestial navigation ages before it was invented by human cap¬tains and plane pilots. It worked fine for the insects, until people ar¬rived in the world. They added lights and lamps all over the place. And this is what baffled the bugs.
Light, as you know, fans out from its source in straight lines. It travels on and on toward us from the stars, the sun and the distant moon. By the time this celestial light reaches us, it is traveling in straight parallel lines.
Flying insects depend on these parallel lines of light to guide them wherever they want to go and back home. They adjust their keen vision so that the distant dependable light falls.on their eyes at a certain angle. As they fly, they keep the same angle coming from the same direction and there is no way to come off course.
When they want to return home, they turn around and adjust their angle of light from the opposite side. The chance of going astray is very slight because stars change their positions very slowly. And at least certain insects can make allowances for the changing positions of the sun and the moon.
However, in other respects the insects are not very bright. They fail to distinguish between street lamps and distant stars. To them the rays of light seem both the same. But they are not. This is because light rays fan out from the source.
When an insect adjusts his vision to a nearby light source, he is in trouble. Instead of being parallel lines, the rays converge toward the center. When he trusts them to guide him, they cause him to fly in a curved instead of a straight path. The curve leads him in a spiral that swirls him closer and closer to the light source which may be a street or patio light, or the scorching flame of a candle.
When the world was young, a flying insect could trust light from the sky to guide him on his way. If the light from the stars struck his eyes at 70 degrees, he maintained this angle and stayed on course. But light rays from a lamp just a few yards away spread out in widening angles. If he adjusts to an angle of, say, 70 degrees, the path spirals inward to the center.