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Moths are nocturnal, so most of what they do is done at night time. In the past, sailors used the sun by day and the stars by night to navigate. Moths used the moon as a reference light and had no trouble flying in the right direction. For thousands of millions of years, this system worked very well, until man invented torches, campfires, candles, and electric lights. Now, moths fly in circles around any bright light, often dying if the light is a flame or a hot lamp. But why?
 
Imagine that the moon is on your left. If you walk forwards in a straight line, the moon will stay on your left. It's so far away, about 230 000 miles, that your short walk won't seem to make any difference to the moon's position, so it's excellent as a navigation reference. Once you know where the moon is, you can move in a straight line in any direction quite easily. The only problem is that, during a long journey, the moon moves across the sky but, with practice, you could learn to adjust your direction.

Now try to do the same thing using a street light that is on your left. If you walk forwards now, you'll lose sight of the light quite quickly. The only way you can keep it in view is if you turn to the left a bit. To keep it in sight all the time, you'll need to keep turning left by walking round it in an anticlockwise circle. Unless you realise that you are not going anywhere, you can easily make smaller and smaller circles.

Moths often get confused by bright lights, particularly on cloudy nights, and fly round and round, often knocking into the light or getting burnt to death.

Copyright and Permission: Learning English 2002

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