If you are near an outside lamp after dark you will notice some insects spiraling around it. Are they simply attracted to the light?
If an insect positions its body in a certain direction and keeps a constant angle with the light rays coming from the Sun or the Moon (which are parallel), it will follow a straight line trajectory. However, people brought to the night sky electric lights emitting radial rays. The insects, continuing to follow the same way of orientation will keep a constant angle with the light rays, but this time they will not fly on a straight line. The trajectory will be an equiangular spiral.
Here are two GeoGebra applets modeling this phenomenon.
Irina Boyadzhiev (author) is a lecturer in mathematics at the Ohio State University at Lima. Her GeoGebra applets are available at: