What causes neurodegenerative diseases such as Parkinson’s  and Alzheimer’s? How are such diseases best treated? For answers to these questions, researchers are probing the neurons of fruit flies and tiny worms called nematodes—and they are making some surprising and useful discoveries.

“Fruit flies have many strengths as animal models of disease,” says Mel Feany, an assistant professor of pathology at Harvard Medical School. The insects are cheap to raise and they mature and reproduce quickly. Their short life span makes studies of mutations, inheritance, and disease progression relatively quick and simple.

Fruit flies have many genes in common with higher animals, including humans. Researchers can easily transplant genes from humans into fruit flies. Finding mutations and observing the characteristics they produce are easier in fruit flies than in other types of animals.

Feany’s laboratory has bred a strain of the fruit fly Drosophila melanogaster that models Parkinson’s disease. Her team implanted mutant genes in the flies for a protein called alpha-synuclein.

Flies carrying the mutant genes lose dopamine-producing neurons in the brain’s substantia nigra, just as humans with Parkinson’s do. Also, fibrous bundles of alpha-synuclein form in the insects’ neurons. Bundles of the same structure and composition (called Lewy bodies) develop in the brain cells of people with Parkinson’s.

Cellular changes in the flies correlate with behavioral changes. Normal fruit flies climb up the sides of plastic vials. Middle-aged flies carrying the transplanted, mutant gene lose that ability.

“They can’t hang on to the sides and just fall to the bottom,” Feany explains. The loss of motor control in the flies mirrors the movement disorders observed in humans who have Parkinson’s.

Fruit flies are not the only simple organisms that have a lot to teach us about neurodegenerative diseases. Chris Li and Angela Hornsten at Boston University have used the nematode Caenorhabditis elegans to study Alzheimer’s disease.