Obtain two glass jars. Paint the outside of one jar completely black so that no light can enter it. Put some house flies or fruit flies in the unpainted jar, then cover it with a stiff piece of cardboard so that the flies cannot escape.

Set the painted jar upside down on top of the cardboard on the unpainted jar. Remove the cardboard. Keep the black jar on top of the clear one, and observe the flies' behavior.

After about five minutes, turn the jars over so that the painted jar is under the unpainted one. Again, observe the behavior of the flies for five minutes.

Now can you guess why flies are usually found near windows?
Flies respond to light -- that is, they move toward light.

If possible, test other animals, such as mosquitoes, spiders, or worms, in the same way to see how light affects them.

Catching live flies is not easy. If you can watch a fly for a minute and see the directions he goes, then you can anticipate his next turn and nab him when he makes the turn.