Towers team eliminated bacteria as a factor by comparing normal fruit flies to specimens born from eggs washed in antibiotic, raised in an axenic environment, and given disinfected food throughout their lives. A third group of flies was raised with bacteria and disinfected in adulthood.

Co-author Paul Webster, director of advanced electron microscopy and imaging at the House Ear Institute in Los Angeles, used scanning electron microscopy to visualize structures resembling bacteria biofilms on the surface of older flies.

Tower and co-author Chunli Ren, a graduate student, took bacteria samples from the surface and interior of the flies throughout their life span, confirming that the axenically grown flies were bacteria-free and that bacteria counts in normal flies increased dramatically as the flies got older.

But all the flies lived about as long approximately three months.