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Richard Morris, age 11, of Oak Hill, West Virginia, for his question:

Why are insects drawn to lights?

Winter is a nice season for recalling those mild summer evenings we spend outdoors. The pesky bugs are not present to annoy us, so we can think of them with calm interest. We can study such problems as why the mayflies and June bugs swarm around street lights and patio lamps. There seems no purpose to it, because this fatal attraction for bright lights draws countless insects to their doom.

Moths are famous for fluttering into candle flames and people used to regard this as an irresistible impulse to commit suicide. But in the past few years, scientists have studied the delicate features of insects and found no suicidal tendencies. Nor is a light irresistible to moths and other night flying insects. Actually, the light interferes with their built in mechanisms for navigating. It draws them off course as they try to fly from here to there.

Most insects seem to fly around hither and thither with no particular destination in mind. But like the bee, who flies home in a straight line, all insects depend on a delicate steering mechanism. This feature developed more than 200 million years ago and helped to make the insects the most successful creatures on earth. It depends on the angles of light rays And the very special eyes of the insect world.

There are simple and compound bug eyes„ with various types of vision. Insects do not see colors as we do and some see into the ultraviolet range which is invisible to us. All colors, of course, are different   wave lengths of light and light is electro¬magnetic energy. Its rays fan out from the source in straight lines. However, when light from the distant sun, moon and stars reaches the earth, its rays are traveling in more or less parallel lines. Rays from a light bulb fan out in widening angles from a nearby local source.

An insect is highly sensitive to the angles at which rays of light strike his eyes. He depends on this device to steer his course. Suppose the light from the sky strikes his eyes at a 70 per cent angle . If he maintains this angle he can depend upon the parallel rays from afar to steer him in a direct line. When he wishes to return or change course, his eyes adjust his steering to a different angle.

This navigation system is reliable when the rays of light from afar are more or less parallel.. But light from a street lamp fans out from a local source. Its angles get narrower toward the center. Suppose the insect comes within range and maintains his 70 per cent course. As the angles of the local rays get smaller, he is steered on a curved path and seems to be drawn spiralling into the center.

For countless ages, the insects steered successfully by light from the sky. They even adjusted their navigation to the changing positions of the sun and the moon. But this ancient system failed when the first caveman lit a campfire. Its rays fanned out from a local source. Their narrowing angles lured night flying insects spiralling down to their doom.

 

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