Perhaps no bug, not even the mosquito, is as widely studied as the fruit fly (Drosophila melanogaster). Scientists have poked at the fruit fly for more than 100 years. They've been able to learn about genetics and how to treat certain diseases including amyotrophic lateral sclerosis (ALS), Parkinson's, Alzheimer's and Huntington's disease.
Fruit flies are well understood and used as a stand-in for humans. That's because we share 75 percent of our genes with the flies. Hundreds of labs in the United States are devoted to fruit fly research. Scientists are not only interested in the bug's genetic makeup, but also in its biology. Plus, they're easy to work with, and scientists can keep millions of them without taking up much space. They can't do that with a rat or a mouse [sources: Jolly, University of North Carolina].