Fruit Fly Lab: Phototaxis, Geotaxis and Chemotaxis (page 2)

Author: Beth Touchette


Fruit flies show a strong negative geotaxis, which means they like to move up. Adult fruit flies generally show a positive phototaxis, meaning they move towards light, but they show some variability in this preference. During your chemotaxis experiment, you should have observed that fruit flies generally move towards the chemicals in their preferred food: rotting fruit.  Sweet substances, wine, and vinegar are often popular fruit fly choices.


A lot of fruit fly behavior can be understood by thinking about how the action helps the fruit fly to better survive in its natural environment. Moving away from gravity makes sense for a flying insect. Preferring light over dark also helps the flies find their food. Many of the chemotaxes you observed can be explained by investigating what fruit flies regularly eat. Since alcohol and vinegar are common byproducts of rotting fruit, you might expect fruit flies to show a strong positive chemotaxis towards them. For your chemotaxes experiment, we asked you to use water as a control to see whether it was the water or the substances dissolved in it that the flies were attracted to.

Going Further

There is so much you can do with fruit flies! Next, you should learn how to tell males from females.  You could repeat your experiment and determine whether one gender likes certain substances more than the other gender does. You also could experiment with fruit fly larvae instead of adults—and if you continue to enjoy experimenting with fruit flies, you might consider doing a genetics experiment.

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